Gr11 Agricultural Sciences SG LR

Via Afrika Agricultural Grade 11 Teacher’s Guide There’s a sort of hidden curriculum that goes Sciences together with the teaching of your subject: in the process of imparting knowledge, you are also imparting values. Grade 11 Study Guide — Americo De Almeida, Teacher P. Oberem, M.E. Moshia, C.F. Reinhardt Via Afrika understands, values and supports your role as a teacher. You have the most important job in education, and we Via Afrika Agricultural Sciences realise that your responsibilities involve far more than just teaching. We have done our utmost to save you time and make your life easier, and we are very proud to be able to help you teach this subject successfully. Here are just some of the things we have done to assist you in this brand-new course: 1. The series was written to be aligned with CAPS. See page 2 to see how CAPS requirements are met. 2. A possible teaching plan has been included. See page 4 and 5 to see how much time this could save you. 3. Each topic starts with an overview of what is taught, and the resources you need. See page 3 to find out how this will help with your planning. 4. There is advice on pace-setting to assist you in completing all the work for the year on time. Page 18 shows you how this is done. 5. Advice on how to introduce concepts and scaffold learning is given for every topic. See page 21 for an example. 6. All the answers have been given to save you time doing the exercises yourself. See page 23 for an example. 7. Also included is a CD filled with resources to assist you in your teaching and assessment. See the inside front cover. The accompanying Learner’s Book is written in accessible language and contains all the content your learners need to master. The exciting design and layout will keep their interest and make teaching a pleasure for you. We would love to hear your feedback. Why not tell us how it’s going by emailing us at agriculturalsciences@viaafrika.com? Alternatively, visit our teacher forum at www.viaafrika.com. Language: English ISBN: 978-1-415-43697-4 9 78 1 4 1 5 436974 www.viaafrika.com

Dawn Webber Study Guide Via Afrika Agricultural Sciences Grade 11 ISBN: 978-1-41546-295-9

Contents Introduction to Agricultural Sciences .....................................................................1 Topic 1 Basic agricultural chemistry ............................................................................................................................................2 overview ........................................................................................................................................................................................................................2 unit 1 Introduction to basic chemistry .......................................................................................................................................3 unit 2 Chemical bonding ....................................................................................................................................................................... 10 unit 3 Inorganic and organic compounds ............................................................................................................................. 13 unit 4 Alkanes and alcohols ............................................................................................................................................................... 19 unit 5 Fatty acids and bio-molecules ........................................................................................................................................ 23 unit 6 Proteins................................................................................................................................................................................................. 28 unit 7 Carbohydrates ................................................................................................................................................................................ 32 topic questions .................................................................................................................................................................................................37 Topic 2 Soil sciences ..................................................................................................................................................................................... 38 overview .................................................................................................................................................................................................................... 38 unit 1 Soil texture ....................................................................................................................................................................................... 40 unit 2 Soil structure .................................................................................................................................................................................. 43 unit 3 Soil colour and soil pores .................................................................................................................................................... 47 unit 4 Soil air .................................................................................................................................................................................................. 50 unit 5 Soil moisture ....................................................................................................................................................................................52 unit 6 Soil temperature ......................................................................................................................................................................... 58 unit 7 Soil morphology ......................................................................................................................................................................... 60 unit 8 Soil classification ....................................................................................................................................................................... 62 unit 9 Soil colloids and soil acidity ............................................................................................................................................ 64 unit 10 Soil alkalinity and soil salinity ..................................................................................................................................... 68 unit 11 Soil organic matter: Living organic matter .......................................................................................................... 71 unit 12 Soil organic matter: Non-living organic matter .............................................................................................. 75 topic questions .................................................................................................................................................................................................77 Topic 3 Plant studies ........................................................................................................................................................................................ 78 overview .................................................................................................................................................................................................................... 78 unit 1 Plant nutrition and photosynthesis .......................................................................................................................... 80 unit 2 Water and nutrients .................................................................................................................................................................. 84 unit 3 Mineral nutrition ......................................................................................................................................................................... 87 unit 4 Plant nutrient uptake and analysis............................................................................................................................. 91

unit 5 Organic and inorganic fertilisers.................................................................................................................................. 94 unit 6 Organic fertilisers and fertilisation practices ................................................................................................... 98 unit 7 Plant reproduction: Sexual reproduction ...........................................................................................................101 unit 8 Plant reproduction: Asexual reproduction ...................................................................................................... 108 unit 9 Plant improvement and biotechnology ................................................................................................................ 115 unit 10 Weed management control ...............................................................................................................................................118 unit 11 Plant diseases and pest control ................................................................................................................................... 123 topic questions ..............................................................................................................................................................................................129 Topic 4 Optimal resource utilisation ...................................................................................................................................... 132 overview .................................................................................................................................................................................................................. 132 unit 1 Soil surveying and planning .......................................................................................................................................... 133 unit 2 Water use and irrigation .....................................................................................................................................................138 unit 3 Soil drainage, cultivation and crop rotation ................................................................................................... 145 unit 4 Greenhouses, hydroponics and aquaculture.................................................................................................. 150 topic questions .............................................................................................................................................................................................. 157 Answers to Topic questions .............................................................................. 159 Exam Practice .................................................................................................. 167 Answers to Exam Practice questions.................................................................. 177

Introduction to Agricultural Sciences Agricultural Sciences is the study of the relationship between soils, plants and animals in the production and processing of food, fibre, fuel and other agricultural commodities that have an economic, aesthetic and cultural value. Agricultural Sciences is an integrated science. It combines knowledge and skills from Physical Sciences, Life Sciences, Social Sciences, Earth Sciences, Engineering, Mathematics and Economics. This subject must be seen within the holistic science framework rather than as an isolated science. In Agricultural Sciences you will: • develop an awareness of the management and care of the environment, natural resources and the humane treatment of animals through application of science and related technology • develop problem-solving mechanisms within the contexts of agricultural production, processing and marketing practices • be aware of the social and economic development of the society at large through personal development in commercial and subsistence farming enterprises • become informed and responsible citizens in the production of agricultural commodities, caring for the environment and addressing social justice issues • be aware of agricultural indigenous knowledge and practices through understanding agricultural sciences in historical and social contexts. Rationale for Agricultural Sciences The interdependence of people and natural resources and the increasing demand on the latter has led to a need for proper utilisation, management and conservation of agricultural and natural resources. Relevant education at secondary school levels can contribute to meeting these demands in a sustainable way. An appreciation and awareness of the importance of natural resources and a responsibility towards their preservation should be fostered from an early age through the Natural Sciences learning area. To fulfil the increasing demand for food and fibre and to meet the aspirations of communities, the acquisition of relevant knowledge, skills, attitudes and values is of vital importance. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 1

1 Topic XX Unit Basic agricultural chemistry Overview ∙ Important terminology • Diﬀerences between elements, molecules, compounds and mixtures UNIT 1 Page 3 • Interpreting the periodic table Introduction to basic • General structure of the atom chemistry • Types of atom particles and their charges • Relationship between atomic numbers and number of particles in the nucleus • Formation of ions • Arrangement of electrons around the nucleus and valency • Diﬀerences between acids and bases UNIT 2 Page 10 Chemical bonding ∙ Basic chemical bonding to form a molecule • Ionic bonding • Covalent bonding ∙ Diﬀerence between inorganic and organic compounds UNIT 3 Page 13 • Formulae, structures and functions of inorganic compounds Inorganic and organic • Characteristics of the carbon atom and organic compounds compounds • Important groups of organic compounds ∙ Basic types of alkanes TOPIC 1 Page 2 UNIT 4 Page 19 • Chemical and structural formulae of alkanes Basic agricultural • Importance of alkanes in plant and animal metabolism Alkanes and alcohols chemistry • Isomers • Basic types of alcohols • Comparison between alcohols and alkanes ∙ Chemical structure of fatty acid UNIT 5 Page 23 • Diﬀerentiation between saturated and unsaturated fatty acids Fatty acids and bio- • Diﬀerences between fatty acids and alcohols molecules • Composition of lipid/fat • Diﬀerences between fats, oils, saturated and unsaturated fats • Functions and importance of lipids/fats UNIT 6 Page 28 ∙ Structure of the monomers of proteins • Diﬀerences between simple and complex proteins Proteins • Structure of polypeptides or simple proteins • Synthesis and hydrolysis of proteins • Functions and importance of proteins in living organisms UNIT 7 Page 32 ∙ Basic chemical composition of carbohydrates • General formulae of carbohydrates Carbohydrates • Structural and chemical formulae of monosaccharides • Main classifications of carbohydrates • Main functions of carbohydrates in living organisms 2 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 XX Introduction to basic chemistry 1 Important terminology Chemistry is the study of the properties, composition and structure of matter, the changes that occur in matter, and the energy that is released during these changes. 1.1 Matter This section defines and explains fundamental concepts in chemistry that apply to all matter or materials. ● The smallest part of matter is an atom. Atoms combine to make up elements, whereas elements make up molecules, and molecules make up compounds. These are all pure substances of matter. ● Objects contain an amount of matter called its mass. The weight of an object is measured by the force with which that object (of a certain mass) is attracted towards the centre of the earth. Although mass and weight are often used interchangeably, their meaning is diﬀerent: mass is a quantity of matter, and weight is a force. ● All matter can be described by a set of characteristics or properties that are unique to it. Intrinsic properties are properties that are common to all samples of the same kind of matter. ● A particular material can be made up of various constituents (parts). ● The way that these are arranged constituents is called the composition of the material. ● The composition of a material shows its structure. ● We need knowledge of the way in which the constituents are arranged, or the structure of the material, to understand how the material will behave and possibly how to change a particular property. ● Elements are structural units of matter that cannot be broken down using chemical methods. ● Elements are pure substances made up of atoms. ● Atoms consist of electrons, neutrons and protons. Examples: carbon (C), oxygen (O), hydrogen (H), chlorine (Cl). ● They adhere to themselves or other elements by chemical bonding to form molecules. ● This bonding process will result in the formation of new pure substances. ● Molecules can be broken down chemically into the elements they are composed of. Examples: carbon dioxide (CO2), water (H2O). ● They can take part in chemical reactions with other molecules by interactions between their atoms. ● Atoms contained in molecules can react chemically to form compounds. ● A pure compound can be broken down or be decomposed to two or more pure substances only by chemical means. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 3

Unit 1 ● A pure substance (element, molecule or compound) is a form of matter whose composition is uniform: All samples of that substance will have the same intrinsic properties. ● A mixture is any material that does not meet the requirement of a pure substance. ● Diﬀerent samples of a specific mixture will have diﬀerent constituents. ● A mixture can be separated into its constituent substances without the need for a chemical reaction. Example: table salt dissolved in water (salt and water are both pure; the mixture can be separated by evaporation of water which is not a chemical reaction). ● We get homogeneous mixtures, heterogeneous mixtures and colloidal mixtures: ● Homogeneous mixture: the composition appears uniform to the naked eye. Examples: seawater and air. ● Heterogeneous mixture: the composition does not appear uniform and samples of the same mixture will contain visibly diﬀerent constituents, e.g. granite (rock of lava origin), fog. ● Colloidal mixture: this is obtained when molecule sizes increase or when clumps of molecules (micelles) occur to form colloids that are only visible using an electron microscope. Colloids do not dissolve in water and form a heterogeneous mixture called a suspension. Examples: protoplasm in living cells, clay minerals in soil. Changes in matter and the role of energy are fundamental in chemistry. ● A chemical change in matter involves the disappearance of one or more substances, and the appearance of one or more new substances, each with its own intrinsic properties. ● Chemical changes are usually accompanied by either the release or the absorption of energy. ● Plants use their leaves to capture the energy of the sun (contained in light particles or photons) in a process called photosynthesis. ● They use this energy to break up carbon dioxide and water that are rearranged to produce carbohydrates → Plants utilise energy stored in carbohydrates through the process of cellular respiration. ● The study of energy changes associated with chemical changes in living organisms is known as biochemistry. ● The Law of Conservation of Energy: energy may be changed from one form to another, but it cannot be created or destroyed. ● Kinetic energy (KE): the energy that matter contains when it is in motion → KE = 0,5mv2 where m is the mass and v is the velocity of the matter. ● Chemical energy: the energy released when coal, which consists of mostly carbonised plant matter, is burned. ● Heat energy: all other forms of energy can be readily converted to heat energy; it is indicated by temperature. 4 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 1.2 The atom The atom is the smallest particle of which matter is composed and the nature of the atom directs the behaviour of matter. ● The word atom originates from a Greek word meaning indivisible. ● Early scholars supported the atomic theory of matter which stated that matter was made up of tiny, indivisible particles which combined to give its characteristic properties. ● Dalton’s Atomic Theory modified the former theory in the early 19th century: ● Idea 1: Elements are composed of extremely small, indivisible particles called atoms. Atoms retain their identity through all chemical reactions. ● Idea 2: Atoms of a particular element have the same average mass, and their other properties are also the same. Atoms of diﬀerent elements generally have diﬀerent average masses and diﬀerent properties. ● Idea 3: Compounds are formed by combinations of the atoms of diﬀerent elements. ● Idea 4: Atoms of two or more elements may combine in more than one ratio to form more than one compound. ● The four ideas contained in Dalton’s Atomic Theory supports the three fundamental laws of Chemistry: ● The Law of Conservation of Mass ● The Law of Constant Composition ● The Law of Multiple Proportions. ● The mass of an atom is usually referred to as its atomic weight. ● Relative weights are used; all weights are expressed relative to the stable form of carbon, 12C, which has an assigned atomic weight of 12. 1.3 Molecules ● Molecules and compounds are formed by the chemical reaction or bonding of atoms. ● Their atomic weight is a function of the atomic weight of their constituent atoms. Example: H2O has a molecular weight of 18,016 (2 1,008 + 16). 1.4 The periodic table of elements The periodic table displays 118 known chemical elements according to selected properties of their atomic structures. (See the next page for an example of a periodic table. ● Elements are in rows in order of their atomic number. ● Elements with similar atomic structure and hence similar chemical properties are arranged in vertical columns called groups. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 5

© Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 13 group number (III) old group number atomic metalloids 5 1 (I) number B Boron symbol name metals non-metals 18 (VIII) period 2 1 H number 2 10.81 13 14 15 16 17 1 He 1 Hydrogen 2 relative Helium 1.0079 (II) atomic (III) (IV) (V) (VI) (VII) 4.0026 3 4 5 6 7 8 9 10 2 Li Be mass 2 B C N O F Ne Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon 6.939 9.012 10.811 12.011 14.007 15.999 18.998 20.180 11 12 13 14 15 16 17 18 3 Na Mg 3 Al Si P S Cl Ar Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon 22.99 24.31 3 4 5 6 7 8 9 10 11 12 28.982 28.098 30.974 32.066 35.453 39.948 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr The reactivity 4 Potassium 39.10 Calcium Scandium Titanium Vanadium Chromium Manganese 40.08 44.96 47.90 50.94 52 54.94 Iron (55.85) Cobalt 58.933 Nickel 58.693 Copper 63.546 Zinc 65.39 4 Gallium Germanium Arsenic 69.723 72.61 74.922 Selenium 78.96 Bromine 79.91 Krypton 83.80 The reactivity of metals 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 of non-metals increases Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe increases up 1 down each 5 Rabidium 85.47 Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium 87.62 88.91 91.22 92.91 95.94 (99) 101.07 102.91 106.42 Silver 107.87 Cadmium 112.41 5 Indium 114.82 Tin 118.71 Antimony 121.76 Tellurium 127.6 Iodine 126.90 Xenon 131.29 each group group 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 85 6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg 6 Tl Pb Bi Po At Rn Caesium Barium Lanthanum Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine Radium 132.9 137.3 138.9 178.5 180.9 183.9 186.2 190.2 192.217 195.08 196.97 200.59 204.38 207.2 208.98 (208.98) (209.99) (222.02) Unit 87 88 89 104 105 106 107 108 109 110 111 7 Fr Ra Ac Db Jl Rf Bh Hn Mt Uun Uuu halogens noble Francium Radium Actinium Dubnium Joliotium Ruthfordium Bohrium Hahnium Mertnerium Ununnilium Unununium (223) (227) (227) (261.11) (262.11) (266.12) (262.12) (265.13) (266.14) (269) (272) gases Reactive transition metals metals Figure 1 The periodic table of elements alkali 58 59 60 61 62 63 64 65 66 67 68 69 70 71 6 Ce Pr Praseody- Nd Pm Sm Eu Gd Tb Dy Ho ER Tm Yb Lu Cerium mium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium 140.1 140.9 144.2 (144.91) 150.36 151.96 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.967 90 91 92 93 94 95 96 97 98 99 100 101 102 103 7 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium 232.04 231.04 238.03 (237.05) (244.06) (243.06) (247.07) (247.07) (251.08) (252.08) (257.10) (258.10) (259.10) (262.1098) 6

Unit 1 1.5 Isotopes ● Isotopes are atoms of the same element with diﬀerent atomic weights. Example: chlorine has an average atomic weight of 35,453 but occurs in nature as a mixture of isotopes with weights of 34,969 (75,53%) and 36,966 (24,47%) ● They have diﬀerent physical properties but the same chemical properties. 2 Interpreting the periodic table The periodic table arranges elements into groups according to their chemical and physical properties. Thus chemists can predict the nature of their reactions with one another and use various chemical methods to build molecules from them. ● The subscript before the symbol for each element (e.g. 12C) indicates the atomic number. ● The atomic number indicates the number of protons in the nucleus. The atomic number is equal to the number of electrons in the electron cloud of one atom of the element. ● Special names are given to certain groups of elements (arranged in columns) that have similar properties: ● Groups I to III can be classified as metals. ● Group I elements are called alkali metals, e.g. lithium (Li), sodium (Na). ● Group II elements are called alkaline-earth metals, e.g. beryllium (Be), magnesium (Mg). ● Groups IV to VII can be classified as non-metals. ● Group VII elements are all halogens, e.g. fluorine (F), chlorine (Cl). ● Group 0 elements are known as noble gases, e.g. helium (He), neon (Ne). 3 General structure of the atom, atom particles and their charges The atom has a small, positively charged core called the nucleus. The atom is electrically neutral and consists of: ● electrons – negatively charged particles → contained in a large outer volume called an electron cloud → surrounds the core of the atom → weighs 1,840 times less than a proton or neutron ● protons – positively charged particles → concentrated in a small inner volume → contain most of the mass of the atom ● neutrons – electrically neutral → occur in the nucleus → mass nearly equal to that of protons. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 7

Unit 1 4 Relationship between atomic numbers and number of particles in the nucleus The symbol for an element can be preceded by a: ● subscript – indicates the atomic number; this is also the number of protons and the number of electrons in one atom (these are always equal in number) ● superscript – indicates the atomic weight. ● Example: 186O : Oxygen has an atomic number of 8 and an atomic weight of 16 (mass of 8 protons + mass of 8 neutrons; 8 electrons have negligible mass) ● Example: 2656Fe : Iron has an atomic number of 26 and an atomic weight of 56 (mass of 26 protons + mass of 30 neutrons; 26 electrons have negligible mass). The number of neutrons is not the same as the number of protons and electrons and thus the atomic weight is not double the atomic number. 5 Formation of ions ● Atoms can either lose or gain one or more electrons to form an ion. ● cation = positively charged ion resulting from the loss of an electron ● anion = negatively charged ion resulting from the gain of an electron. ● The charge on an ion is shown by a superscript after the symbol, e.g. K+ (+ means +1). ● ions with opposite charges are attracted to one another ● ions with the same charge are repelled ● if the charge of the atoms add up to zero then the molecule is neutral. 6 Arrangement of electrons around the nucleus and valency Valence electrons ● are the outermost electrons around an atom ● are the most likely to be involved in chemical reactions ● help to explain the combining power or valency of atoms. An element usually has the same number of valence electrons as its group number. ● Na is in Group I and has a single valence electron → upon ionisation it loses one electron to form the cation, Na+ ● Noble gases in Group 0 do not react readily react with other elements and have 8 valence electrons, except for helium (He) which has a valence number of 2. ● Some elements have a fixed valence, e.g. sodium (Na) and potassium (K) always have a valence of 1 when they take part in chemical reactions. ● Many elements have a variable valence, e.g. iron (Fe) can have a valence of 2 (as in FeCl2) or 3 (as in FeCl3). 8 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 7 Differences between acids and bases The definition of acids and bases is as follows: ● An acid is a substance that can donate a hydrogen ion or proton (H+). ● A base is a substance that can accept a hydrogen ion, or yield a hydroxyl ion (OH–) when dissolved in water. ● Examples: ● HCl → H+ + Cl– (HCl is the acid which donates H+). ● HCl + H2O → H3O+ + Cl– (reactions usually occur in water; H2O is the base which accepts H+). ● NaOH → Na+ + OH– (NaOH is the base which yields OH–). The pH of a solution indicates the concentration of H+ ions and it can range from 0 to 14. ● It is defined by pH = –log[H+]. ● If [H+] > [OH–] then the pH is high and the solution is acidic (i.e. pH < 7). ● If [OH–] > [H+] then the pH is low and the solution is basic or alkaline (i.e. pH > 7). ● If [H+] = [OH–] then the pH is 7 and the solution is neutral (e.g. water). © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 9

Unit 2 XX Chemical bonding 1 Basic chemical bonding to form a molecule There are two main ways in which electrons can interact in a chemical reaction: ● ionic bonding – electrons are transferred from one atom to another ● covalent bonding – electrons are shared between atoms. Two other types of bonding are also important in the formation of compounds: ● hydrogen bonding – a strong, electrostatic attraction between a hydrogen atom and an electronegative atom, e.g. nitrogen, oxygen, fluorine ● Van der Waals attractions – an attractive force between molecules. The outermost electrons in the electron cloud of atoms take part in chemical reactions to form chemical bonds. The number of valence electrons in an atom determines the ratio in which atoms enter into combinations with each other. ● These valence electrons are spread in shells around the nucleus of an atom. ● Moving outwards from the nucleus, each shell represents a higher level of energy of the electron found in that shell. ● The electrons usually fill the lowest shell or energy level first. ● Chemical bonds form when two or more atoms interact to fill their outer shells with electrons. This happens as follows: ● As the atoms approach each other, each nucleus begins to attract the electron held by the other nucleus. ● Eventually, the electron clouds overlap and fuse into one molecular orbital. ● Like an atomic orbital, a molecular orbital is most stable when filled by a pair of electrons. ● This shared orbital acts as a chemical bond between the two atoms. ● The number of electrons needed to fill each shell diﬀers from shell to shell. 1.1 Chemical formulas and formula weight The atomic weight of the elements in a compound can be used together with its chemical formula to calculate the formula weight of the compound. ● Chemical formula = combination of the symbols for atoms that make up a compound. ● The symbol for each element represents one mole of atoms of that element. ● The term mole is used as a unit for the amount of a substance. ● Avogadro’s number is 6,02 1023 and represents the number of atoms in exactly 12 g of the element carbon, which has an atomic weight of exactly 12. ● Thus 6,02 1023 elementary particles (of anything) is equal to 1 mole (of that thing). 10 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 ● Examples: ● 1 mole of hydrogen contains 6,02 1023 atoms and weighs 1,008 g ● 1 mole of KCl contains 6,02 x 1023 ions of K+, 6,02 x 1023 ions of Cl– and weighs 74,55 g (39,10 g K + 35,45 g Cl) ● The formula weight (or molecular weight) of Na3PO4 is: 3Na = 3 22,99 = 68,97 g PO4 = 30,97 + 4(16,00) = 94,97 g = 163,9 g 1.2 Oxidation number and chemical bonding An element’s oxidation number, sometimes called valence, is the number of electrons gained or lost when forming compounds. The concepts may be defined as follows: ● Oxidation: the loss of electrons (usually from left to right in a chemical reaction). ● Reduction: the gain of electrons (usually from right to left in a chemical reaction). ● Oxidation number: the charge of an atom if the compound was composed of ions only. ● Example: Cu+1 ←→ Cu+2 + e– ● Cu+1 loses one electron and is oxidised to Cu+2 ● Cu+2 gains one electron and is reduced to Cu+1 ● Cu+1 has an oxidation number of +1 and Cu+2 has an oxidation number of +2. ● Example: CaCO3 ● CaCO3 contains Ca+2 and CO3–2 ions ● Since calcium exists as Ca+2 in its ionic state, it has an oxidation number of +2. 2 Ionic bonding Example: Potassium bromide (KBr) contains an ionic bond. ● Potassium (K) is in Group I and has one valence electron → upon ionisation it can donate one electron and form the cation, K+. ● Bromine (Br) is in Group VII and has seven valence electrons → upon ionisation it can receive one electron to form the anion, Br–. ● K donates one electron to Br, and Br receives one electron from K (i.e. transfer of an electron from K to Br), thus forming an ionic bond. ● The strong electrostatic attraction between oppositely charged ions forms a stable bond. 3 Covalent bonding Electrons are shared in a covalent bond and this can occur between: ● atoms of identical elements, e.g. Cl2 ● atoms of diﬀerent elements, e.g. H O. 2 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 11

Unit 2 ● Hydrogen (H) is in Group I and has one valence electron. ● Oxygen (O) is in Group VI and has six electrons of which two are valence electrons available for bonding. ● Oxygen shares each of its two electrons with one hydrogen atom resulting in the formation of two covalent bonds. 3.1 Polarity When two atoms of diﬀerent elements form a bond, one atom will have a stronger attracting power or electronegativity. ● The shared electron cloud will be closer to the more electronegative element. Example: ● In a H2O molecule, oxygen is more electronegative than hydrogen. ● Thus, O obtains a partial negative charge and the water molecule has a negative pole, whereas H obtains a partial positive charge and represents two positive poles. ● → The water molecule is called polar. ● Only covalent molecules can possess this polarity. 3.2 Hydrogen bonding This is a very strong type of electrostatic interaction between two water molecules. ● The negative pole (that is, oxygen) and the positive pole (that is, hydrogen) of adjacent water molecules are attracted to one another. ● This linkage is called a hydrogen bond. ● It gives water many unique properties including its ability to aggregate together and form a body of water, as well as: ● flexibility and flow characteristic ● unexpectedly high boiling or vaporisation point ● greater density than ice ● ability to act as a solvent for a wide range of substances ● capacity to absorb high levels of heat energy before its temperature is raised ● high surface tension. 3.3 Van der Waals inter-molecular attraction This is a collective name for the weak attractive forces that hold molecules together. ● They occur between molecules. ● They are much weaker than ionic and covalent bonds. ● Hydrogen bonding is the strongest type of van der Waals interaction. 12 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 XX Inorganic and organic compounds ● All green plants use simple inorganic compounds (nutrients) to form complex organic compounds. ● Example of nutrients: ● carbon dioxide (CO2), nitrate (NO3–), sulphate (SO4–), and phosphate (PO4–3). ● Most plant tissue is made up of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulphur (S), and phosphorus (P). 1 Difference between inorganic and organic compounds ● Inorganic compounds do not contain carbon and hydrogen atoms in the same molecule. ● e.g. sodium chloride (salt), ammonium hydroxide (used in household cleaners). ● Organic compounds contain both carbon and hydrogen atoms (called hydrocarbons). ● e.g. ethane, butane, acetone. Plants are divided into two groups based on the type of nutrients they require. ● Autotrophic organisms: ● require only simple, inorganic nutrients to make complex organic compounds ● e.g. all green plants, certain bacteria. ● Heterotrophic organisms: ● require small amounts of inorganic nutrients ● mostly break down complex organic materials in their food to obtain nutrients. ● e.g. all animals and humans, certain parasitic plants. 1.1 Inorganic compounds serving as nutrients The environment is made up of three compartments: air, water and soil. ● These can all provide elements that are essential for the growth of plants. ● Thus, essential environmental factors for plant growth are: ● air, water, light, heat, mechanical support (e.g. soil or other plants) and nutrients. ● Soil can supply these factors, either completely or in part, except for light. ● All factors are needed and an imbalance will result in poor plant growth. Principle of limiting factors: ● The level of plant (crop) production can be no greater than that allowed by the most limiting of the essential plant growth factors. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 13

Unit 3 About 95% of the fresh mass of plant material consists of C, H and O. ● Seventeen elements are essential for normal plant growth. ● Needed in large amounts: ● C, O (obtained from air via photosynthesis) ● H (obtained from water taken up from soil) ● N, P, K, Ca, Mg, S (available in soil; some nitrogen taken up from air in soil by nitrogen-fixing bacteria on plant roots → called N-fixation) ● Needed in small amounts: ● Fe, Mn, B, Mo, Cu, Zn, Cl, Co (available in soil). Although not essential, plants grow better with: ● soluble forms of sodium (Na) ● silicon (Si) ● iodine (I) ● fluorine (F) ● barium (Ba) and ● strontium (Sr). 2 Formulae, structures and functions of inorganic compounds Lewis structures may be used to represent the covalent bonding in a molecule or ion. ● Bonds between atoms are shown by lines: ● → two electrons are needed to form a bond. ● Lone pairs of electrons (not involved in bonding) are shown by dots or crosses next to the atoms. Most elements prefer to be surrounded by 8 electrons (the octet rule) except for hydrogen: ● → has only two electrons. ● e.g. Hydrogen fluoride (HF) ● hydrogen (H) has one single electron ● fluorine (F) has seven electrons: three lone pairs, one single electron ● H and F use their single electrons to form a bond between the atoms → represented by a line ● F still has three lone pairs and these are shown as three pairs of dots around F. 14 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 2.1 Water (H2O), carbon dioxide (CO2) and ammonia (NH3) Table 1 Useful information about water, carbon dioxide and ammonia Water Carbon dioxide Ammonia Occurrence: • Seas, rivers, lakes (liquid); • Atmosphere (0,03%); • Main source is decomposed • Atmosphere (as a vapour); • Volcanic gases; animal and plant waste • Makes up 80% of living • Respiration product of all (contains N) organisms living things; • Fuel combustion product Structure: Properties: • No colour, odour or taste; • Odourless, colourless, non- • Gas that condenses at -33 °C; • Density of 1 at 4 °C; poisonous gas; • Highly water soluble • Melting point 0 °C; • Freezing point -76 °C; • Boiling point 100 °C • Reacts with water to form carbonic acid Importance: • Main solvent on Earth and • Plants use CO2 and H2O • Plant and animal nutrition; ionisation in water facilitates to build complex organic • N source for protein reactions; compounds; synthesis by bacteria, • Main source of H, O; • Excreted by animals during plants and animals • Transport medium in the body; respiration • Regulates Earth’s temperature 2.2 Mineral salts Needed by living organisms for nutrition, usually inorganic (do not contain C). ● Plants obtain from soil and humans from their food. ● e.g. Sodium chloride or table salt (NaCl) ● Occurrence: halite (pure rock salt), mixed evaporates in salt lakes, seawater ● Structure: ● Properties: clear (when pure), water soluble, slightly soluble in other liquid, odourless, characteristic taste. ● Importance: maintain salt/water ratio in the body, maintain electrolyte balance of cells, required for hydration of the body. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 15

Unit 3 3 Characteristics of the carbon atom and organic compounds ● Carbon (C) atoms form the backbone of organic compounds. ● They can be linked to another C atom by one (single), two (double) or three (triple) covalent bonds. ● Saturated organic compounds have a maximum number of hydrogen (H) atoms bonded to the C atoms. ● Unsaturated organic compounds contain one or more double or triple bonds in their C skeleton. 3.1 The most important characteristics of carbon Two important characteristics of carbon allow it to act as the basis for the chemistry of life: ● it has four valence electrons ● forms stable and reactive molecules (because of the energy required to make or break a bond). 3.2 The most important characteristics of organic compounds The characteristics of organic compounds are similar to that of covalent compounds. ● volatile ● low melting and boiling points ● insoluble in water; soluble in organic solvents ● poor conductors of electricity ● do not provide ions ● take part in molecular reactions. Usually the reactions of organic compounds are slow, never proceed to completion and produce low yields. 4 Important groups of organic compounds Carbon combines with four other simple inorganic elements to make up most of the organic tissue components of all living organisms: ● proteins ● carbohydrates ● lipids ● nucleic acids. 16 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 Table 2 Basic groupings of organic compounds Organic com- Elements contained in Functions pound compound Proteins C, H, O, N, S, P • biological catalysts • form structural parts of organisms • participate in cell signalling and recognition • act as molecules of immunity Carbohydrates C, H, O • major food and energy source • carbohydrate polymers are: long-term food storage molecules, protective coverings for cells and organisms, main structural support for land plants, cell constituents Lipids C, H, O, N, S, P • major cell membrane constituents • food storage molecules • e.g. fats, oils, waxes Nucleic acids C, H, O, N, P • storage of organism’s heritable information and its conversion into proteins • e.g. deoxyribonucleic acid (DNA), ribonucleic acid (RNA) – two major classes 4.1 Examples of organic compounds Table 3 Summary of different organic compounds (R is any radical or hydrocarbon) Compound Basic structure Example How it is formed Alkanes Saturated hydrocarbon, only Methane single bonds CH4 Alcohols R–OH (OH: hydroxyl group) Methanol Formed from alkane CH3–OH Thiols R–SH CH3–SH Readily oxidise to form disulphide bridge: RS–SŔ Ethers R–O–R Dimethyl ether CH3–O–CH3 Aldehydes R–CO–H Acetaldehyde Oxidation of alcohol (C=O double bond) CH3–CO–H Ketones R–CO–Ŕ Dimethyl ketone (C=O double bond) CH3–CO–CH3 Acids R–CO–OH Acetic acid Oxidation of alde- (C=O double bond; COOH: CH3–CO–OH hyde carboxyl group) Salts –COO(X+) Sodium acetate H of carboxyl group (X: element that can form CH3–CO–ONa replaced with a cation) cation Esters R–CO–OŔ Ethyl acetate Reaction of acid and CH3–CO–OCH3 alcohol © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 17

Unit 3 Table 3 Summary of different organic compounds (R is any radical or hydrocarbon) Compound Basic structure Example How it is formed Amines R–NH2 Methyl amine H of alkane replaced CH3–NH2 with NH2 group Amides R–CO–ONH2 Acetamide OH of acid replaced CH3–CO–ONH2 with NH2 group Cyclic Contain one or more ring Benzene, C6H6 structures Phenols One or more OH groups on Phenol, C6H5OH benzene ring or Heterocycles Ring structure containing one Pyran, C5H5O or more N or O atoms Sugars Simple: less than five C, no Glucose ring; Complex: six C, ring structure 18 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 XX Alkanes and alcohols 1 Alkanes Alkanes are organic compounds that consist of hydrocarbon chains that are fully saturated. The four simplest examples are: ● methane (one carbon) ● ethane (two carbons) ● propane (three carbons) ● butane (four carbons). 1.1 Basic types of alkanes and their chemical and structural formulae 1.1.1 Methane ● Principal component of natural gas: ● = most abundant compound on Earth. ● Formed through an anaerobic (i.e. involving oxygen), multi-step respiration process called methanogenesis: ● = CO2 + 8H+ + 8 e– → CH4 + 2H2O (net reaction). ● Produced by microbes in oxygen-starved environments ● e.g. such as swamps, landfills. ● Also produced by the gut of ruminants ● e.g. cattle. ● Important biogas produced on industrial scale through the fermentation of organic material. ● Farmers use methane gas produced by decomposing faeces and plant matter to provide the energy for their farms. ● Chemical formula: CH4. ● Structural formula: Figure 2 Structural formula of methane © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 19

Unit 4 1.1.2 Ethane ● Colourless and odourless at standard (room) temperature and pressure. ● Second-largest component of natural gas. ● Chemical formula: C2H6 or CH3–CH3. ● Structural formula: Figure 3 Structural formula of ethane 1.1.3 Propane ● Normally found in gas form, but compressible to a transportable liquid. ● By-product of natural gas processing and petroleum refining ● Chemical formula: C3H8 or CH3–CH2–CH3. ● Structural formula: Figure 4 Structural formula of propane 1.1.4 Butane ● Highly flammable, colourless and easily liquefied. ● Chemical formula: C4H10 or CH3–CH2–CH2–CH3 or CH3(CH2)2CH3. ● Structural formula: Figure 5 Structural formula of butane Chemical properties of alkanes ● Inert at room temperature, but burn in air at higher temperatures. ● Gradually move from gaseous form to solids as the length of the carbon chain increases. ● React with most halogens in the presence of sunlight. 20 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 1.2 Importance of alkanes in plant and animal metabolism ● Basic building block for many compounds occurring in plants and animals. ● Play a role in the biology of the three eukaryotic groups of organisms: fungi, plants and animals. For example: ● some yeasts use alkanes as a source of carbon and/or energy. ● Long-chain alkanes form a protective wax layer over plants; protects against water loss and bacteria, fungi and harmful insects. 1.3 Isomers Isomers are compounds with the same molecular formula, but a diﬀerent structural formula. ● Simplest isomer exists as a single chain and is called the n-isomer. ● Only alkanes with more than three carbons can exist as isomers. Example: ● C4H10 can exist as n-butane (four carbons arranged linearly) and isobutene (central carbon is bonded to three carbons). 2 Alcohols Alcohols are hydroxyl derivatives of alkanes and they are named after the alkanes from which they are derived. They have a hydroxyl group (OH) in the place of a single hydrogen (H) atom in the corresponding alkane. 2.1 Basic types of alcohols and their structures There are three types of alcohols and they diﬀer according to the position of the OH group. Table 4 Basic alcohols and their structures Type Primary alcohol Secondary alcohol Tertiary alcohol Position of OH attached to the terminal C; attached to a C atom linked attached to a C atom linked group exception: methanol to two other C to three other C Examples ethanol isopropanol isopentanol Structural formula © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 21

Unit 4 2.2 Importance of basic alcohols ● Alcoholic beverage industry: fermentation of sugars to ethanol is used in the production of wine and other alcoholic beverages. ● The same process occurs in plants in the absence of oxygen (anaerobic conditions) and results in a build-up of ethanol and subsequent tissue damage. ● Ethanol is an important, renewable source of energy. ● The energy contained in ethanol originates from sugars stored in plants following photosynthesis. ● The release of this energy is used as fuel to provide cooling, heating, lighting, movement and sound. ● Industrial applications: fermentation is performed by organisms (e.g. yeasts) that produce the enzyme pyruvic decarboxylase. 22 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 XX Fatty acids and bio-molecules 1 Fatty acids Fatty acids may be thought of as long-chain carboxylic acids. They are attached to the glycerol backbone of lipid molecules. 1.1 Chemical structure of a fatty acid ● General chemical formula: R-COOH. ● a carboxyl functional group (COOH) is attached to the terminal carbon atom ● R is a long, unbranched fatty hydrocarbon chain consisting of 12–24 carbon atoms. O R C OH organic molecule carboxyl group (COOH) Figure 6 The general chemical structure of a fatty acid 1.2 Differences between saturated and unsaturated fatty acids The hydrocarbon tail of fatty acids can either be saturated or unsaturated. 1.2.1 Saturated fatty acids ● No double bonds between carbon atoms of the fatty acid chain. ● Normally solid at room temperature. ● Mostly of animal origin. ● Foods containing a high proportion of saturated fat: ● animal fats, e.g. cheese, fatty meats ● vegetable products, e.g. coconut oil, chocolate. ● Examples of saturated fatty acids: ● butyric acid = CH3(CH2)2COOH ● lauric acid = CH3(CH2)10COOH Figure 7 The structural formula of two saturated fatty acids: butyric acid (left); lauric acid (right) ● Saturated fatty acids play a vital role in nutrition and bodily functions, but they should be consumed in moderation. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 23

Unit 5 XX ● Their importance is shown by the following: ● provide the appropriate stiﬀness and structure to our cell membranes and tissues ● strengthen the immune system ● involved in inter-cellular communication (e.g. protect against cancer) ● involved in the function of cell membrane receptors (e.g. protect against diabetes) ● lung and kidney function, hormone production ● suppress inflammation ● saturated animal fats carry fat-soluble vitamins A, D and K2 which promote good health. 1.2.2 Unsaturated fatty acids ● One to three double bonds between carbon atoms of the fatty acid chain. ● Monounsaturated: ● one double bond. ● Polyunsaturated: ● more than one double bond. ● One to eight carbons: ● occur in liquid form. ● More that eight carbons: ● occur as solids. ● Properties relevant to saturated fatty acids: ● lower melting points (melting point decreases as number of double bonds increases) ● contain less energy, i.e. fewer calories ● more vulnerable to lipid peroxidation. ● Foods containing unsaturated fatty acids: avocado, nuts, and vegetable oils, meat products (together with saturated fats). Figure 8 The structural formulae of a monounsaturated (left) and polyunsaturated (right) fatty acid. ● Left: Palmitoleic acid (16 carbons), CH3(CH2)5CH=CH(CH2)7COOH, ● Right: Linoleic acid (18 carbons), CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Double bonds may be in either a cis or a trans conformation. ● cis isomer: ● occurs when hydrogen atoms are on the same side of the double bond ● is less flexible as the number of double bonds in the chain increases. ● e.g. oleic acid (18 carbons), CH3(CH2)7CH=CH(CH2)7COOH (the most abundant fatty acid found in nature). 24 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 ● trans isomer: ● occurs when hydrogen atoms are on the opposite side of the double bond ● do not cause the chain to bend much; sometimes known as trans fatty acids. ● e.g. vaccenic acid (18 carbons), CH3(CH2)5CH=CH(CH2)9COOH. Double bonds introduce ‘kinks’ in the carbon chain resulting in the fluid nature of lipid membranes. Figure 9 The structural formula of a cis-unsaturated fatty acid (oleic acid, left) and trans-unsaturated fatty acid (vaccenic acid, right) In Figure 8 above, all three double bonds are in the cis conformation. Importance of polyunsaturated fatty acids ● Contained in high amounts in membranes of animal and plant cells. ● Found in fish and a range of nuts and provide nutritional benefits, e.g. lower risk of heart attack and some cancers. 1.3 Classification of fatty acids Fatty acids can be classified according to two factors: ● Nature of the bonds between carbon atoms of the fatty acid chain: ● single bonds only: saturated fatty acid ● one double bond: unsaturated fatty acid ● multiple double bonds: polyunsaturated fatty acid. ● Number of carboxyl groups (-COOH): mono-, di- or tricarboxylic acids. 2 Lipids Lipids are a naturally occurring group of molecules that includes: ● fats, oils and waxes ● sterols (e.g. cholesterol) ● fat-soluble vitamins (e.g. vitamins A, D, E, and K). They are defined according to their solubility, i.e. they are all soluble in non-polar organic solvents, and not according to a physical property. The solubility of lipids is due to the presence of a large hydrocarbon portion in their structure. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 25

Unit 5 2.1 Basic composition of lipids The general structure for fats, oils and waxes is shown in the figure below. They all contain three ester functional groups (i.e. –O–CO–R). These three ester functional groups are attached to a glycerol backbone. Figure 10 Basic structure of fats, oil and waxes An important group of lipids is the phospholipids. Their structure is similar to the general structure of fats, waxes and oils except that a phosphate molecule is attached through an ester bond with the terminal carbon atom of the glycerol backbone. Figure 11 An example of a phospholipid Phospholipids have a strong polar character due to the nature of their two ends: ● strongly hydrophilic phosphate molecule ● strongly lipophilic (or hydrophobic) fatty acids. This makes them important components of membrane structures since they are held together by hydrophobic and polar interactions only. 2.2 Differences between fats and oils, and saturated and unsaturated fats The distinction between fats and oils is based on the nature of the fatty acids from which they were derived, i.e. whether the fatty acids are saturated or unsaturated: ● saturated fatty acids produce unsaturated fats ● unsaturated fatty acids produce unsaturated fats or oils. ● polyunsaturated fatty acids produce polyunsaturated fats or oils. 26 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 They also diﬀer in their phase at room temperature: ● Fats tend to be solid at room temperature. ● Oils tend to be liquids at room temperature. ● This is influenced by: ● size and molecular weight ● kink caused by a cis double bond which prevents the orderly arrangement of molecules required by the solid phase. 2.3 Main functions of lipids ● Energy storage ● primary means of storing energy ● rapidly broken down to CO2 and H2O with the release of high amounts of energy. ● Waterproof coverings ● this is achieved by waxes and oils in various species ● plants have coatings on their leaves ● mammals have oils found on skin, hair and nails. ● Cell membranes ● membranes are composed mainly of lipids ● allow for fluid movement and transport of molecules in and out of cells. ● Protection ● excess lipids are stored as fats ● act as insulators of internal organs. ● Hormones ● some lipids function as hormones ● they regulate stress responses, sugar levels, and sex cell production ● Absorbing vitamins ● lipids carry vitamins out of the intestines and store them in fatty tissues, e.g. ● vitamins A, D, E and K. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 27

Unit 6 XX Proteins 1 General structure of the monomers of proteins Proteins are polymers that are formed through the combination of amino acid molecules. Proteins are composed of a single, unbranched chain of amino acid monomers. ● Amino acids: ● general formula H2NCHRCOOH ● made up of carbon, hydrogen, oxygen and nitrogen atoms ● R is an organic substituent (or side-chain) ● there are 20 possible side-chains ● functions: allow ligand binding and protein folding, provide catalytic activity, stabilise final conformation. ● central carbon to which R group is attached is called the alpha () carbon: ● -carbon is called chiral and has an L-configuration ● examples: glycine, R=H; alanine, R=CH3. amino NH2 group carboxyl H C COOH group R Figure 12 General structure (left) and formula (right) of an amino acid 1.1 Essential and non-essential amino acids Plants are able to make all the amino acids but humans do not have all the enzymes required for the biosynthesis of the 10 essential and 10 non-essential amino acids. Table 5 Essential and non-essential amino acids Essential amino acids Non-essential amino acids • cannot be synthesised by the organism (usually • synthesised by the body from essential humans); amino acids • must be supplied in the diet daily (typically from meat and dairy products); • obtained from degradation of proteins if they are lacking arginine (not for adults), histidine, isoleucine, leu- alanine, asparagine, aspartic acid, cysteine, cine, lysine, methionine, phenylalanine, threonine, glutamic acid, glutamine, glycine, proline, tryptophan, valine serine, tyrosine 28 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 6 2 Differences between simple and complex proteins Amino acids are linked together by peptide bonds and they may also be cross-linked between chains by sulphydryl bonds, hydrogen bonds and Van der Waals forces. Table 6 Simple and complex proteins Simple proteins Complex proteins Definition only contain amino acids contain amino acids and other substances; or function with other chemical groups attached by covalent bonds or by weak interactions Hydrolysis amino acids and occasional small carbo- amino acids and other chemical compo- products hydrates nents Examples albumins, globulins lipoproteins, glycoproteins 3 General structure of polypeptides or simple proteins Proteins are made up of amino acids covalently linked by peptide bonds. ● Peptides = short chain polymers (< 30 amino acids). ● Polypeptides or proteins = longer chain polymers. Peptide bond formation: ● occurs between COOH of one amino acid and NH of an adjacent amino acid 2 ● occurs in a condensation reaction during which a water molecule is lost. 3.1 The structural levels of polypeptides or simple proteins ● Primary structure: ● the amino acid sequence of the protein, i.e. the nature of the amino acids and the order in which they are bonded. ● Secondary structure: ● local structural arrangement stabilized by hydrogen bonds ● e.g. alpha helix (coiled or spiral appearance), beta sheet (twisted strand). ● Tertiary structure: ● overall shape of protein and the spatial relationship between secondary structures ● stabilised by interactions between side-chains, e.g. Van der Waals bonds, hydrogen bonds, covalent bonds. ● Quaternary structure: ● formed by several protein molecules which function as a single protein complex ● structures held together by ● hydrogen bonds ● disulphide bonds ● polar and ● non-polar bonds. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 29

Unit 6 XX 4 The synthesis and hydrolysis of proteins 4.1 The synthesis of proteins Proteins can be built up from amino acids with a particular primary, secondary, tertiary and even quaternary structure to serve particular functions. ● Proteins are polymers that are formed through the combination of amino acid molecules or monomers. ● The amino acid monomers – using dehydration synthesis – bond together to form proteins (or polypeptide chains). ● Dehydration synthesis is a condensation reaction because water is removed in the formation of the bonds. ● The condensation reaction occurs between the acid carboxyl group (–COOH) and the amino (–NH2) group. ● The bonds that are formed in dehydration synthesis are called peptide bonds. ● A chain of more than three amino acids held together by peptide bonds is called a polymer or a polypeptides chain. monomer monomer monomer H H O H H O H H O N C C N C C N C C H R1 OH + H R2 OH + H R3 OH Condensation reaction H2O H2O produces water H H O H H O H H O N C C N C C N C C peptide peptide bond bond OH H R1 R2 R3 polypeptic chain Figure 13 Synthesis of a protein polymer by condensation 4.2 The hydrolysis of proteins ● Involves breaking of a peptide bond in a protein. ● reverse process of protein synthesis ● requires water, i.e. dipeptide + water → amino acid + amino acid. 4.2.1 Protein breakdown in organisms In animals, proteins are obtained mainly in food. ● Stomach: gastric juices contain hydrochloric acid and pepsin, an enzyme that breaks down proteins. 30 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 6 ● Small intestine: other enzymes (trypsin and chymotrypsin) break down proteins further. ● once completely digested, proteins / amino acids are absorbed ● energy is released and waste products are produced (urea in humans and animals, uric acid in birds and land reptiles, CO2 and water in plants). 5 The functions and importance of proteins in living organisms Proteins may be grouped according to their main functions. This function is influenced by the structure of the protein. Table 7 Function and importance of proteins Protein Function Example Antibodies defend the body from antigens (foreign invaders) by immunoglobulin = a large immobilising them so that they can be destroyed by Y-shaped protein produced by B- white blood cells cells that is used by the immune system to identify and neutralise foreign objects such as bacteria and viruses Contractile responsible for movement actin = muscle contraction and proteins movement Enzymes facilitate/ speed up biochemical reactions pepsin digestive enzyme = breaks down proteins in food in the stomach Hormonal messenger proteins that help co-ordinate bodily somatotropin = growth hormone proteins activities that stimulates protein produc- tion in muscle cells Structural maintain the structures of certain biological compo- collagen = support connective tis- proteins nents, such as cells and tissues sues like tendons and ligaments Storage contain energy which can be released during meta- ovalbumin = found in egg whites proteins bolic processes Transport carrier proteins that move molecules from one place haemoglobin = transports oxygen proteins to another around the body in blood © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 31

Unit 7 XX Carbohydrates 1 Composition and formation of carbohydrates Carbohydrates are energy-rich organic compounds. ● Living organisms use a process called respiration to convert carbohydrates to energy, water and carbon dioxide. ● Examples: sugars, starches, cellulose ● Composed of carbon (C), hydrogen (H) and oxygen (O) atoms. ● atoms occur in a set proportion = one C atom, to two H atoms, to one O atom 2 General formulae of carbohydrates ● General formula: Cx(H2O)x ● Basic building blocks: ● Monosaccharides or simple sugars (names end in -ose). ● Disaccharides: ● composed of two monosaccharides joined by a glycosidic bond ● formed in a condensation (or dehydration) reaction in which water is released: ● 2(CxH2xOx) → C2xH2x–2O2–1 + H2O ● e.g. 2(C6H12O6) → C12H22O11 + H2O ● Polysaccharides: ● composed of more than two monosaccharides ● formed in a condensation (or dehydration) reaction ● monosaccharides first become monomers and then bond with other monomers ● e.g. C6H12O6 → C6H10O5 → (C6H10O5)n (monosaccharide) (monomer) (polysaccharide) 3 Structural and chemical formulae of monosaccharides Monosaccharides are divided into groups depending on their number of carbon atoms. ● Triose: 3 carbons, e.g. glyceraldehyde (C H O ). 3 6 3 ● Tetrose: 4 carbons, e.g. D-erythrose (C H O ). 4 8 4 ● Pentose: 5 carbons, e.g. ribose (C H O ). 5 10 5 ● Hexose: 6 carbons, e.g. D-allose (C H O ). 6 12 6 32 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 H O O H H O H O C C C C H C OH H C OH H C OH H C OH CH2OH H C OH H C OH H C OH CH2OH H C OH H C OH CH2OH H C OH CH2OH Figure 14 Structural formulae of monosaccharides (from left to right): Triose, Tetrose, Pentose and Hexose 4 Main classifications of carbohydrates ● Monosaccharides: simple sugars. ● Oligosaccharides (including disaccharides): short-chain polymers of 2 – 6 monosaccharides. ● Polysaccharides: very long chain polymers of monosaccharides. Carbohydrates have diﬀerent properties depending on their classification: ● Monosaccharides, oligosaccharides = crystalline, water soluble, often sweet-tasting ● Polysaccharides = non-crystalline, usually insoluble in water, tasteless 4.1 Monosaccharides ● Simple aldehydes or ketones. ● Molecules prefer to adopt a closed-chain / ring structure. ● Ring forms due to an attraction between the aldehyde / ketone and the alcohol group. ● Three important hexose isomers: ● glucose, fructose and galactose. H O C CH2OH H C OH C O HO C H HO C H HO C H H C OH H C OH H C OH CH2OH CH2OH Figure 15 Two of the most important hexose isomers (left) galactose and (right) fructose © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 33

Unit 7 ● Calvin Cycle (or the carbon reduction cycle): ● sequence of reactions that build the carbon from CO2 into monosaccharides ● i.e. CO2 → monosaccharides ● six CO2 molecules are required to build one molecule of hexose ● intermediate products act as building blocks for the synthesis of amino acids, proteins and lipids 4.1.1 Glucose ● Most well-known monosaccharide sugar. ● chemical formula: C6H12O6 ● primary source of energy in cells ● major product of photosynthesis ● starts cellular respiration ● exists as two isomers: ● -glucose (alpha glucose) ● -glucose (beta glucose). H O C CH2OH CH2OH H C OH C O H O H HO C H or C OH C OH HO C H C C OH OH H C OH HO HO CH2OH OH OH Figure 16 The open-chain (left) and closed-chain (right) structures of glucose 4.1.2 Ascorbic acid ● Important glucose derivative: ascorbic acid (or Vitamin C). ● synthesised in plants and animals but not in primates (humans and apes) and guinea pigs. 4.2 Disaccharides ● Specific enzymes are involved in the linkage of particular monosaccharides to form disaccharides. Examples of disaccharides: ● glucose + glucose → maltose ● glucose + galactose → lactose ● glucose + fructose → sucrose. 34 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 4.3 Polysaccharides ● Storage polysaccharides: sources of energy, occur in plants and animals. Examples: ● starch and glycogen. ● Both consist of very long chains of glucose molecules ● amylose + amylopectin → starch (unbranched glucose chain) (branched chains of glucose) ● glycogen is similar in structure to amylopectin ● Examples of structural polysaccharides: ● cellulose in plant cell walls, chitin in insect and fungi skeletons, pectin in fruit. 5 The main functions of carbohydrates in living organisms Carbohydrates are obtained mainly from diet in animals whereas plants synthesise their own via photosynthesis. 5.1 Carbohydrates in animals ● Primary source of energy: ● carbohydrates are converted to energy which is used for important cellular functions ● fats and proteins can be an alternative energy source but toxic ketone bodies can accumulate and lead to ketosis (blood becomes unable to carry oxygen properly). [by enzyme hydrolysis] [oxidation reaction] polysaccharides → glucose* → CO2 + H2O + energy Figure 17 Conversion of carbohydrates to energy in animals * glucose is transported between cells by blood (animals) or cell sap (plants) ● Carbohydrates also: ● act as storage food, e.g. glycogen is stored in the liver and muscles ● act as an anticoagulant and prevents intravascular clotting, e.g. heparin ● act as an antigen and provides blood with immunological properties ● act as a hormone and helps in reproductive processes, e.g. FSH and LH ● used in laxatives, e.g. agar ● provide frictionless movement, e.g. hyaluronic acid found between joints. 5.2 Carbohydrates in plants ● Main structural material for cell walls, e.g. cellulose and lignin. ● Photosynthesis: plants produce their own carbohydrates in the form of glucose. ● Cellular respiration: plants store carbohydrates and burn them for energy. ● Food source: plants produce sugars from sunlight (i.e. by photosynthesis) and make these available to organisms that use plants as their food source. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 35

1X Topic XX Unit Topic questions ● Answer the questions below. ● Give yourself one hour. ● Check your answers afterwards and do corrections. 1 Define the following terms: a molecule b isotope c valence electron d Provide examples for a) and b). (5) 2 Describe the general structure of an atom with special reference to the three components. (6) 3 Complete the following sentences: a Sodium is a/an ___ found in Group I of the periodic table. b The group VII elements are called noble gases and ___ is an example. (2) 4 Provide a term to match the following descriptions. a A type of chemical bonding in which electrons are shared between atoms. b This is equivalent to the charge of an atom if the compound was composed of ions only. c The combination of the symbols for atoms that make up a compound. d A term used to describe a water molecule that has oxygen atoms with partial negative charges and hydrogen atoms with partial positive charges. e A strong, electrostatic attraction between a hydrogen atom and an electronegative atom such as oxygen. (5) 5 The molecular weight of calcium chloride (CaCl2) is: a 151,06 g b 110,98 g c 75,53 g d (1) 6 Explain the flexibility and flow characteristic of water. (3) 7 There are many elements that are essential for normal plant growth. a Name two nutrients obtained via photosynthesis that are required in large amounts. (2) b Name two nutrients that are available in soil and needed in small amounts. (2) 36 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

1X Topic XX Unit Topic questions 8 Provide the Lewis structure for carbon dioxide and describe its importance. (6) 9 Refer to the given examples and provide a name for the type of each organic compound. (4) a CH3–OH b CH3CH2–CO–H c CH3–CO–ONH2 10 The following questions are about methane. a Provide a chemical formula. (1) b Name the chemical process by which it is formed. (1) c Is it the most abundant or the second most abundant compound on Earth? (1) 11 Name the most basic alcohol that contains three carbon atoms. Is it a primary, secondary, or tertiary alcohol? (2) 12 Answer these questions about fatty acids and bio-molecules. a Explain the term fatty acid and describe the diﬀerence between saturated and unsaturated fatty acids. (4) b Name the type of isomer that causes a saturated fatty acid to ‘bend’ the most? (2) c Name four of the main functions of lipids. (4) 13 Draw the basic structure of an amino acid (use R for the variable group). (4) 14 Explain what is meant by an essential amino acid. (2) 15 Discuss protein synthesis in plants. (4) 16 Complete the following sentences about carbohydrates. a Disaccharides are composed of two ___ joined by a ___ bond. (2) b Disaccharides are formed in a ___ reaction in which water is released. (1) c Hexose sugars contain ___ carbon atoms and the three most important hexose isomers are galactose, glucose and ___. (2) d Glucose is the major product of ___. (1) e Two glucose units bond to form the disaccharide ___. (1) f Carbohydrates are the main source of ___ in animals. (1) g Carbohydrates are the main structural material for cell ___ in plants. (1) Total: 70 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 37

Topic 2 Unit X XX Soil sciences Overview UNIT 1 Page 40 • Main groups of soil particles Soil texture • Soil textural classes, their determination and their importance • Influences of sand and clay particle size on soil characteristics • Classification of soil structures UNIT 2 Page 43 • Factors influencing the development and stability of soil structure Soil structure • Factors or malpractices that cause soil structure to decline • Methods to improve poor soil structure • The advantages of good soil structure UNIT 3 Page 47 Soil colour and soil • The concept: soil colour pores • Soil pores TOPIC 2 Page 38 UNIT 4 Page 50 • Factors that aﬀect storage and movement of soil air Soil sciences Soil air • Comparison between atmospheric and soil air • Important soil gases • Basic types of soil water and their characteristics • A description of soil water losses and ways to limit these losses UNIT 5 Page 52 • Forces of nature that have an eﬀect on soil water Soil moisture • The diﬀerent movements of water through the soil • Availability of soil water to a plant at diﬀerent limits of soil water content • Scientific methods to illustrate capillary and gravitational movement of water in soil • Eﬀective soil water management UNIT 6 Page 58 • The main factors influencing soil temperature and their measurement Soil temperature • Eﬀects of soil temperature on physical, chemical and biological processes in soils • Methods to manipulate soil temperature for better production UNIT 7 Page 60 • The terminology: soil profile, soil horizon and profile whole Soil morphology • The development and description of master horizons • Soil profiles • A practical identification of topsoil and subsoil horizons 38 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Topic 2 Unit X XX Soil sciences Overview UNIT 8 Page 62 • The binomial soil classification system in South Africa Soil classification • Diagnostic horizons of topsoil and subsoil horizons • The benefits of soil classification in agriculture UNIT 9 Page 64 Soil colloids and soil • Soil colloids acidity • Soil acidity • The concept: soil alkalinity (predominant cations) UNIT 10 Page 68 • The concepts: saline soils and sodic soils • Characteristics of saline or white brack soils Soil alkalinity and soil • Factors causing brackishness, soil alkalinity or salinity saltiness • The eﬀects of alkaline or brack on crop productivity TOPIC 2 Page 38 • Methods to prevent or control soil alkalinity • Reclamation of alkaline or brackish soils Soil sciences • Importance and role of soil micro-organisms and macro-organisms • Main groups of soil micro-organisms UNIT 11 Page 71 • Main groups of soil macro-organisms Soil organic matter: • Requirements for soil micro- and macro-organisms Living organic matter • The carbon cycle and conversion by soil micro-organisms • The nitrogen cycle and conversion by soil micro-organisms • The phosphorus cycle • The process of symbiosis UNIT 12 Page 75 • Definitions of fresh organic matter and humus • Eﬀects of organic matter on soils Soil organic matter: • Factors that aﬀect the balance of organic matter in soils Non-living organic • Eﬀects of the decline in organic matter on soil degradation matter • Making a compost heap © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 39

Unit 1 XX Soil texture 1 Main groups of soil particles ● Soil texture: ● is defined as the relative proportions of sand, silt, and clay particles in a mass of soil ● includes only the inorganic solid fraction of soils ● proportions of sand, silt and clay are expressed as percentages (determined in a soil laboratory) ● → textural classes are then assigned, based on the composition of the soil determined. Soil particles are divided up into groups based on their diameter. ● It is important to include detail about diameter when conducting a soil survey because particle size has a big influence on physical properties of a soil. Table 1 Main groups of soil particles Clay Silt Sand smallest soil particles clay < silt < sand particles largest soil particles (coarse) only seen with a microscope only seen with a microscope seen without microscope or magnifying glass dry particles: smooth and dry particles: smooth and floury powdery wet particles: smooth, not slick wet then dried: hard and sticky wet particles: slick, sticky, holds mould easily clayey soils: sandy soils: = 30–35% clay < 20% clay, > 50% sand e.g. sandy clay, silty clay, clay e.g. sand, loamy sand, sandy loam soils divided according to particle sizes: coarse, medium and fine 2 Soil textural classes, their determination and their importance 2.1 Textural classes of soils ● Soils are classified using the soil textural triangle (see Figure 1). This triangle: ● can be classified into 12 classes with increasing proportion of fine particles: ● sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, clay. 40 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 ● Sand, silt, and clay soil particles are often called soil separates: ● help scientists understand the behaviour of soil (e.g. with regard to nutrients, water holding capacity, compaction). 100 10 90 20 80 30 70 clay 40 ay 60 pe r nt cl r ce 50 cen 50 silty ts pe ilt clay sandy 60 40 clay clay silty clay 70 30 loam loam sandy clay loam 80 20 loam sandy loam silty loam 90 10 loamy silt 10 0 sand sand 10 90 80 70 60 50 40 30 20 10 0 per cent sand Figure 1 The soil textural triangle 2.2 Determination of textural classes of soil The textural class of soils may be determined in one of two ways: ● analyse soil composition in a laboratory and use the soil textural triangle ● analyse soil in the field and estimate the soil textural class. Commercial soil analysis laboratories in South Africa use two methods involving particle size analysis. ● Hydrometer method: ● disperse soil particles with sodium hexametaphosphate (NaPO3)6 or Calgon agitate soil particles ● determine amount of each particle group in the suspension using a hydrometer ● apply Stokes Law to calculate the particle diameter. ● Pipette method: ● same concept but diﬀerent instrument used to sample ● only used when quantity too small for hydrometer method ● = more accurate but less convenient method. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 41

Unit 1 After analysis, the soil textural triangle can be used to classify the soil texture. ● Two field methods may be used to determine the soil textural class. ● Sausage method: moisten a small amount of soil in your hand, roll between your hands and try to form a sausage. Use a sausage method chart to classify according to when the breakage takes place: ● high amounts of clay → forms a sausage ● high amount of sand → forms a ball but not a sausage ● in between amounts of clay → break during sausage-making process. ● Feel method: moisten a small amount of soil in your hand and rub between your thumb and forefinger – ● clayey soil → feels slippery or greasy ● sandy soil → feels rough ● silty soil → feels floury. 2.3 Importance of textural classes of soil ● The textural class of soil aﬀects many factors including: ● seed germination ● water holding capacity ● drainage properties ● root development ● pesticide movement. ● Therefore, this knowledge will allow the farmer to: ● maximise productivity e.g. ● cultivating suitable crops, addition of appropriate nutrients ● minimise environmental harm, e.g. ● cover cropping in sandy soils to reduce wind erosion. 3 Influences of sand and clay particle size on soil characteristics ● Properties of sandy soils: ● Low water holding capacity ● = poor for dryland farming. ● Low organic matter content ● = can improve by adding organic fertilisers. ● Well aerated ● = easy to handle in tillage operations. ● Properties of clayey soils: ● Low infiltration rate ● = when dry, hard clay soils limit seed germination. ● Poorly drained and aerated ● = become waterlogged in rainy seasons. 42 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 XX Soil structure Soil structure refers to the arrangement of: ● solid parts of the soil ● the pore spaces between. Soil particles Ped individual particles aggregate peds stacked particles to form a ped around each other to form soil structure Figure 2 Assembly of soil particles to form soil structure Note: ● peds: produced by natural processes; ● clods: produced by improper cultivation Soil structure influences: ● water movement into soil ● heat transfer ● aeration ● porosity. Soil structure is aﬀected by: ● agricultural activities, e.g. ● ploughing, cultivating, manuring. ● weather, e.g. ● wetting and drying in humid climates. 1 Classification of soil structures Soil structure is studied in situ (in the field under natural conditions). It is described according to: ● type (or shape) ● class (or size) and ● grade. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 43

Unit 2 Table 2 Classification of soil structures Type or shape Class or size Grade shape or form and arrangement size of structural units or peds degree of distinctness of of peds structural units or peds • spheroidal: granular, crumb • very fine / fine • weak • platy • medium • moderate • prismatic and columnar • coarse / very coarse / extremely coarse • strong • blocky: angular, subangular • (each can be applied to the different types) 1.1 Classification according to type or shape ● Spheroidal soil structure: ● consist of individual particles of sand, silt and clay grouped together in small, nearly spherical grains ● found mostly in the topsoil (A-horizon) ● water circulates very easily through such soils. ● Platy soil structure: ● consist of thin, flat, horizontal peds that look like plates stacked on top of another ● found in the surface horizon (i.e. E-horizon), subsoil, compacted soils, the horizon of forest soils ● root penetration and water circulation are diﬃcult. ● Prismatic and columnar soil structures: ● consist of vertical columns or pillars separated by small vertical cracks ● tops of the columns are either flat (prismatic) or rounded (columnar) ● found in the B-horizon in sub-humid to semi-arid areas where clay has accumulated ● water circulation, drainage and aeration = poor. ● Blocky soil structures: ● consist of irregularly-shaped blocks, each can be broken into smaller block peds ● structure is approximately cubic ● found in medium-textured to clayey subsoils (B-horizon) in sub-humid to semi- arid areas. 2 Factors influencing the development and stability of soil structure The development and stability of soil structure depends on natural factors and agricultural activities. ● Aggregate formation and aggregate stability: ● clay soil particles are required because they have cohesive forces to bind particles together → high clay content soils will have more tightly formed soil structures. 44 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 ● Cementing agents help form aggregates: ● soil invertebrates ingest soil and produce faeces that maintain structure ● fungi use hyphae that extend into soil to connect particles together ● bacterial polysaccharides resist decomposition thus holding soil particles together ● roots excrete sugars that bind minerals ● iron oxides act as glue ● aluminium oxide binds sand and silt particles ● dehydration of colloidal matter and pressure completes the aggregation process. ● Climate: ● aﬀects degree of aggregation and type of soil structure ● little aggregation in arid regions ● greater degree of aggregation in semi-arid regions. ● Organic matter: ● improves structure of sandy and clayey soil ● sticky and slimy substance produced on decomposition cements sandy particles ● reduces cohesiveness and makes clay more crumbly. ● Tillage: ● breaks large clods into aggregates ● optimum moisture content is necessary. ● Electrostatic forces: ● soil particles are naturally attracted through electrostatic forces. 3 Factors that cause soil structure to decline Soil aggregates are important because the spaces between them allow root penetration and movement of air and water. Aggregates may be destroyed in several ways leading to a decline in soil structure. ● Poor tillage practices: ● e.g. overuse of ploughing, addition of excessive chemical fertilisers ● → cause loss of nutrients and ability to store water ● → decrease water infiltration rate ● → reduce organic matter. ● Compaction: ● cracks and pores are compressed by heavy farm machinery ● → cause reduced oxygen diﬀusion ● → cause reduced infiltration of water, thus erosion and overland flow ● Loss of organic matter: ● humus can withhold water and nutrients ● → gives plants the capacity for growth. ● humus can help soil stick together ● → allows bacteria to decay nutrients. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 45

Unit 2 ● Poor irrigation water: ● high salt content can destroy soil structure ● therefore, analyse soil for EC and SAR (electrical conductivity, i.e. soluble salts; Sodium Adsorption Ration, i.e. suitability of irrigation water for agricultural land) ● → high SAR means that Na+ in irrigation water can replace Ca2+ and Mg2+ in the soil, decreasing the ability of the soil to form stable aggregates 4 Methods to improve poor soil structure ● Increase organic content: ● incorporate pasture phases into cropping rotations. ● Green manuring: ● grow suitable cover crops and plough these back into the soil to increase organic matter. ● Reduce or eliminate tillage and cultivation. ● Avoid soil disturbance: ● → soil may shatter or smear during periods of excessive dry or wet. ● Ensure suﬃcient ground cover: ● = to protect the soil from raindrop impact. ● Apply gypsum (calcium sulphate) to irrigated land: ● → displace sodium cations with calcium cations to reduce exchangeable sodium percentage and thus water quality. 5 The advantages of good soil structure Good soil structure will increase productivity and enhance sustainability in many ways. ● Soil compaction: ● avoid compaction to improve porosity ● → improves water infiltration rate, retention and availability. ● Crusting: ● reduce soil surface crusting to improve the emergence of seedlings ● crusts cause poor infiltration, reduced air exchange between soil and atmosphere. ● Soil erosion: ● soil aggregate strength results in decreased overland water flow and soil erosion. ● Salt imbalances: ● avoid salt imbalances to improve ability to form stable aggregates. ● Limit the eﬀect of a drought and excessive wetness: ● good soil structure results in increased water storage capacity and infiltration rate. 46 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 XX Soil colour and soil pores 1 The concept: soil colour Soil properties are influenced by biological activity, water movement and weathering. ● Soil colour is the first physical property used to diﬀerentiate soil horizons. ● Colour changes with soil depth and is directly related to various soil properties: ● homogeneous colour: particular soil mineral occurs in large enough quantities ● non-homogeneous colour: mixture of colours (called mottled) due to wetting and drying. 1.1 Main factors that determine soil colour ● Amount of organic matter: ● usually topsoil (i.e. A-horizon) is dark or black. ● Presence of compounds and elements: ● iron oxides: yellowish-brown to reddish colour ● manganese oxides: purplish-black soil colour ● calcium carbonate: white ● carbon compounds: black. ● Drainage: ● poor drainage results in light grey colour or rust-like spots (mottles) – ● referred to as bleached or washed out. ● Leaching: ● loss of iron compounds and coloured minerals results in light colour. Table 3 Interpretation of soil colours dark rich in nutrients and organic matter contains iron compounds, e.g. hematite (Fe2O3) red well-drained (highly oxidised iron compounds are red) iron and manganese loss due to leaching light lack of organic matter soils that are developed from quartzite yellow, yellow/ iron present at lower levels than in red soil, e.g. goethite (FeOOH) brown more poorly drained than red soil very poor drainage grey, iron and manganese compounds in reduced form due to the lack of air blue-grey called gleyed soils poor aeration mottled waterlogged or fluctuating water table © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 47

Unit 3 2 Soil pores Pores are the part of the soil occupied by soil atmosphere and water. Total pore space (or porosity) is the volume of soil occupied by air and water. ● Two types of pores: ● Macro pores: ● large ● allow free movement of air and water ● under the influence of gravity. ● Micro pores: ● very small ● retain water and prevent drainage, thus determine water retention or storage capacity ● use capillary forces. 2.1 Factors that influence total pore space ● Soil texture and soil structure: ● determine micro pore volume and thus water storage capacity ● finer textures (i.e. higher clay content) have more micro pores and thus larger storage capacity ● good soil structure increases total porosity: large pores between aggregates allow movement of water and air. ● Soil depth: ● pore space decreases with soil depth ● subsoil tends to be more compacted than topsoil. ● Soil cultivation: ● excessive or intensive tillage destroys soil aggregates, reduces organic matter and causes compaction ● organic matter can be used to increase soil retention. 2.2 Soil bulk density and porosity Soil bulk density (Db) is the mass of oven-dried soil per unit volume of soil. ● Soil bulk density accounts for soil solids and spaces between soil particles (pore space) ● → high proportion of pore space leads to a low bulk density. ● Some Db values: ● typical mineral soils: 1,0–1,6 g cm–3 ● compacted soils: → 1,6 g cm–3 ● soils with high proportion of organic matter: < 1,0 g cm–3. ● Soil bulk density can be determined in an undisturbed, dried soil sample ● use a soil bulk density core sampler ● dry soil at 105 ºC for 48 hours. 48 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 ● Soil bulk density can be used to: ● assess potential for leaching of nutrients and erosion: high bulk density can restrict movement of surface water ● estimate total water storage capacity (when soil moisture content is known). Bulk density provides an indirect measure of the soil porosity (amount of pore space). ● Soil porosity: ● is the ratio of the volume of soil pores to the total soil volume – ● clayey soils: abundance of very small pores (micro pores) → higher total porosity ● sandy soils: larger, but fewer pores → lower total porosity. No particles = 100% Porosity 100 80 % Porosity 60 Solid particles = 40 0% Porosity Aggregated Sandy soil 20 clayey soil 0 0 0.5 1 1.5 2 2.5 3 Bulk Density (g cm-3) Figure 3 The relationship between soil bulk density and porosity 2.3 Factors that influence the bulk density of soil ● Organic matter content: ● high organic content leads to larger pore spaces and lower soil bulk density ● Texture: ● finer textured soils (clays and clay loams) usually have adequate organic matter content. ● Pore spaces: ● large pore spaces occur when soils are not compacted which lowers bulk density. ● Depth in the profile: ● at deeper levels there is less organic matter and aggregation, fewer micro- organisms and more compaction which increases bulk density. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 49

Unit 4 XX Soil air 1 Factors that affect storage and movement of soil air A soil ecosystem consists of air, water, minerals, organic matter, and macro- and micro- organisms. A constant flow of air is required. Thus, soil must not be over-saturated with water because this would exclude air. ● Factors that aﬀect soil air ● Macro pores: ● facilitate drainage and diﬀusion of air ● content determined by soil texture, bulk density, aggregate stability, organic matter ● pore content determines pore volume which determines soil aeration. ● Soil depth or soil horizon: ● topsoil horizons are better drained thus oxygen occupies their soil pores ● soils with a crumb structure have macro pores. 2 Comparison between atmospheric and soil air ● The percentage composition of atmospheric and soil air is very similar with regard to: ● oxygen = approximately 20% ● nitrogen = approximately 79% and ● carbon dioxide = <1%. ● The following points about soil air should be noted: ● usually saturated with water vapour ● may contain volatile contaminants ● contains more CO2 and less O2 (seasonal) ● greater variation in composition within soil and over time. 3 Important soil gases 3.1 Oxygen ● Provides for respiration of plant roots and soil organisms. ● Lack of oxygen causes a CO2 build-up: ● → stunts plant growth. ● Needed for ● seed germination ● decomposition of organic material. ● Facilitates the release of energy from the oxidation of carbon. 50 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 ● Important in chemical weathering – ● → iron oxide is realised into the soil (haematite, Fe2O3) ● → binds particles together. 3.2 Carbon dioxide ● Carbon dioxide is the product of respiration of plant roots and soil organisms: ● soil micro-organisms mix CO2 with water to form carbohydrates ● CO2 gas dissolved in water forms carbonic acid ● → important in chemical weathering 3.3 Nitrogen ● Most important element for plant development: ● must be processed naturally in the soil or added as fertiliser. ● Waterlogged soils contain N2 gas (reduced form) ● → unavailable for crops. ● Well-drained and aerated soils contain oxidised nitrogen ● → provides crop-available nutrients ● = nitrate (NO3–) and ammonium (NH4+). © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 51

Unit 5 XX Soil moisture 1 Basic types of soil water and their characteristics Table 4 Types of soil water Gravitational water Capillary water Hygroscopic water found in soil macro pores found in soil micro pores forms thin films around soil particles moves through soil due to force held against pull of gravity by held on particle surface by of gravity cohesion and adhesion forces; adhesion forces; micro pores exert more force on force of gravity is counteracted water than macro pores by forces of attraction between water molecules and soil particles and by attraction of water molecules to each other not available to plants; moves available for plant growth not available to plants; rapidly out of well-drained soil held tightly by soil so not taken (2–3 days) up by roots occupies air space needed to supply oxygen to roots, so up- land plants may wilt and die 2 A description of soil water losses and ways to limit these losses Table 5 Soil water losses and some solutions Drainage Transpiration Evaporation removal of water by gravity or loss of water vapour through loss of water from soil surface in pumping; stomata on leaf surfaces (mainly) vapour form; rapid in soils with large pores and plant stems; influenced by crop shading and (i.e. sandy soils) accounts for 90% of losses amount of water available at soil surface solution: solution: solutions: improve field capacity by adding controls weeds which may con- plant groundcover or increase organic matter tribute to transpiration surface shading; plant windbreaks; provide physical structures that concentrate rainwater 3 Forces of nature that have an effect on soil water ● Adhesion: ● attraction between soil particle surfaces and water molecules ● → results in water being held tightly by soil particles. 52 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 ● Cohesion: ● like molecules sticking together ● water molecules are cohesive due to strong hydrogen bonds that form between them. ● Capillarity: ● additive force of adhesion and cohesion ● describes ability of a liquid to flow against gravity and rise spontaneously in a narrow space, e.g. ● stem of a plant ● explains movement of groundwater from wet areas of the soil to dry areas. ● Adsorption: ● adhesion of water to solid soil surfaces ● capillary and adsorptive forces together result in soil matric potential or matric force. ● Matric force: ● holds water from the surface of soil particles ● → due to attraction of soil particles to water and cohesive forces between water molecules ● water always moves from state of high to low energy ● easier for plants to obtain water when the soil is moist than when it is dry. ● Field capacity (FC) is the upper limit of soil water available to plants, and permanent wilting point (PWP) is the lower limit. ● Electrostatic forces: ● retention of water molecules on soil surface based on dipole character of water ● interaction of positive and negative charges of water with negative charge of soil particles creates successive layers of oriented water molecules ● orientation becomes weaker as the layer thickens until capillary water begins to appear. ● Bonding forces ● responsible for formation of water molecules (i.e. when H and O bond to form H2O) ● responsible for water storage in soil: ● adhesive forces: result of chemical bond between water and exchangeable cations in soil colloids, and polar groups of soil minerals and organic matter ● cohesive forces: due to hydrogen bonding of additional water molecules ● large pores drains quickly due to gravitational forces ● smaller pores are under capillary forces and are resistant to drainage ● only a portion of the water stored in the soil is available to plants. ● As the amount of water in the soil increases, the energy with which it is held decreases. ● As the amount of water in the soil decreases, the strength of bonding of water to the soil solids increases. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 53

Unit 5 4 The different movements of water through the soil 4.1 Movement of liquid water in soil There are two ways in which liquid water moves through soil and they determine the amount of water available to plants. ● Saturated flow: ● all the pores are full of water, i.e. macro and micro pores ● water at the surface of the soil possesses a high potential ● → depends on the diﬀerence in potential between two points, the soil and the ease with which the soil allows the water movement (i.e. hydraulic conductivity). ● Unsaturated flow: ● micro pores are filled with water and macro pores are filled with air ● → water flows through micro pores and the surface of the soil particles (lower negative potential) to another zone of a higher negative potential ● → water moves from moist soil (lower negative potential) to dry soil. 4.2 Movement of water vapour in soil Vapour flow occurs only in relatively dry soil where vapour pressure diﬀerences are significant. There are two types of vapour flow. ● Mass flow: ● water vapour flows in a mass along with other soil gases ● → as atmospheric pressure decreases, gases expand and escape the soil ● → as atmospheric pressure increases, gases contract and enter the soil. ● Diﬀusion flow: ● diﬀusion is the property by which two gases readily mix when in contact ● → water evaporates from moist / warm soil and the vapour diﬀuses into the adjacent dry / cool soil ● it is due to a diﬀerence in temperature. 5 Availability of soil water to a plant at different limits of soil water content Soil water is available to plants at diﬀerent limits of soil water content. Soil water content describes how much water a soil can contain at diﬀerent limits. ● Saturation point: ● all soil pores are filled with water ● also called maximum moisture holding capacity of the soil ● occurs after rainfall. ● Saturation capacity can be expressed as centimetre of water per metre of soil depth. 54 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 ● Field water capacity: ● soil water content after soil has been saturated and drained freely for 1–2 days ● free drainage occurs by force of gravity ● remaining water is held with a force greater than that of gravity. ● Temporary wilting point: ● due to higher transpiration on hot windy days ● plants recover during cooler part of the day ● does not require any addition of water. ● Permanent wilting point: ● soil moisture percentage at which plants cannot obtain enough moisture to continue growing (i.e. when they die) ● plant roots take up available water or water vapour ● → dry out without additional water ● → remaining water is tightly retained and plant roots cannot extract it. ● depends on ● rate of water usage by the plant ● depth of the root zone ● water holding capacity of the soil. 6 Capillary and gravitational movement of water in soil Capillary action and the gravitational movement of water are two forces that have an eﬀect on soil water. ● Capillary action allows water to flow up plant stems. ● Gravitation movement of water allows water to move downwards through the soil. 7 Effective soil water management Soil water management is based on the manipulation of the soil water balance. 7.1 Soil water balance ● Soil water balance (SWB) reflects all quantities of water added, removed or stored in a given volume of soil during a given period of time. ● The term water balance, when applied to a crop or soil system, describes what happens to precipitation and the various components of water flow in and around the soil profile: ● precipitation (P) – rainfall, and/or irrigation – is the major water input to the crop or soil system ● P aﬀects surface runoﬀ water (R), crop evapotranspiration (ET), deep percolation (DP) and changes in soil water storage (S): ● P = R + ET + DP + S ● Understanding SWB helps farmers manage soil water more eﬀectively. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 55

Unit 5 Energy source Precipitation (P) - Rain and irrigation Evapotranspiration (ET) Evapotranspiration (ET) Runoff (R) Changes in water storage (S) Deep percolation (D) Figure 4 The water balance cycle 7.2 Components to consider in management strategies ● In the above water balance formula, only transpiration can promote crop growth and yield: ● therefore: transpiration must be kept high to maximise yield ● → all the other components except P result in a loss of water ● → they must be managed eﬀectively. Table 6 Components to consider in water management strategies Evaporation driven by energy of the sun striking soil restrict solar energy reaching soil surface: surface, speed in which moist air is re- cover with stubble mulch; moved (wind), moisture content of soil do not irrigate frequently; use deeper irrigations at longer intervals Interception extent to which a crop holds water in its use deeper irrigations at longer intervals canopy; directly related to size and density of crop canopy Runoff occurs when precipitation rate exceeds improve soil structure by adding organic water infiltration rate; compost; infiltration rate depends on soil structure, apply water more efficiently based on soil texture and water content texture; adjust irrigation time and duration Drainage uncontrolled drainage below root depth soil moisture content must be near to field wastes water; capacity to make water available to plants; can flush out excess salt from roots reduce soil moisture content during rainy season (prevent runoff) 56 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 7.3 Effective management strategies ● Firstly do the following: ● check how much water you have (in storage or have access to) ● understand your crop water needs ● have access to a nearby weather station ● know the organic matter content, soil depth, structure, texture, and water holding capacity of the soil on your farm. ● Then undertake the following strategies: ● regularly review your volume of water (stored and available) ● design and monitor an irrigation programme ● use only amount of water required and monitor usage with rain gauges ● irrigate later in the day and not during windy conditions ● application rate of water should not exceed infiltration rate of soil. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 57

Unit 6 XX Soil temperature 1 The main factors influencing soil temperature and their measurement Soil obtains its energy from solar radiation. Table 7 Main factors influencing soil temperature and their measurement Moisture content • influenced by rate at which soil warms up and • use soil moisture sensors cools off: moist soils warm more slowly than dry • soil moisture content is highly variable soils • aircraft and satellites use remote sensing tech- • condensation increases temperature nology to enhance the variation • rainfall decreases temperature • measures uppermost layers of soil and provides • specific heat capacity and thermal conductivity data on energy variations influences temperature • presence of water has a strong influence on temperature: water has high heat capacity so it takes less heat to raise soil temperature in dry soil Soil colour • dark soils absorb more energy from the sun and • soil thermometer can be used heat more quickly • measurements should be done on a summer • cultivated soil has a greater temperature afternoon for accurate results Direction of slope • solar radiation that reaches the land surface at • use of lines of latitude to simulate changes in an angle is scattered over a wider area direction of exposure and degree of slope • South Africa is in the southern hemisphere so northern facing mountain slopes are warmer Soil cover • vegetation and cloud cover intercepts direct • compare temperature under a shady tree with sunlight bare soil • cloud cover also insulates soil from temperature • compare temperature between rows of healthy changes crop close to reproductive stage with nearby bare soil 2 Effects of soil temperature on physical, chemical and biological processes in soils ● Soil temperature influences: ● nutrient cycling ● microbial processes ● plant growth rates ● root functions ● water storage. 58 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 6 ● Two main categories: ● chemical and physical processes ● biological processes. 2.1 Chemical and physical processes affected by soil temperature ● Chemical and physical processes aﬀect decomposition and mineralisation of organic matter ● → thus aﬀect nutrient availability. ● Soils with high temperatures experience accelerated rates of mineral weathering. ● Rates and depth of evaporation increase with soil temperature. ● Increased viscosity at low soil temperatures decreases: ● the rate of nutrient transport to the roots ● water uptake rate of the roots ● water transport rate within the plant. 2.2 Biological processes affected by soil temperature ● Biological processes aﬀect growth and physiology of plant root systems ● → thus aﬀect nutrient uptake ● → amount and duration of root growth, root morphology, and root spatial distributions ● → rates of ion uptake, root respiration, cell membrane permeability, and transport in xylem. 3 Methods to manipulate soil temperature for better production ● Tillage and shaping of fields: ● slope angle and direction aﬀect soil temperature ● modify soil thermal properties by specific tillage practices, e.g. ● ridging and shaping. ● Mulching and vegetation: ● used for water conservation and soil temperature manipulation e.g. ● straw, weed or trash, gravel, plastic, paper, aluminium foil. ● Shading and row spacing ● artificial shading, e.g. ● net or transparent plastics ● row spacing and plant population. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 59

Unit 7 XX Soil morphology 1 The terminology: soil profile, soil horizon and profile hole The weathering of rocks into smaller pieces to form soil is a key process that directs soil formation. The outcome is a complete soil profile with various soil horizons. ● Several factors influence soil formation and the development of a soil profile: ● Parent material: unconsolidated material that provides most of soil horizon character. ● Climate: rainfall and temperature influence the rate of weathering. ● Topography: arrangement of physical features (e.g. slope) that influences the vegetation and soil type of a location. ● Time: soil formation is extremely slow → so a younger soil profile reflects the parent material more closely. ● Organisms: type and number of organisms are important ● → influenced by plants. 2 The development and description of master horizons South Africa uses the South African Binomial System of Soil classification: ● Master soil horizons: O, A, E, G, B, C, and R. ● Subdivisions of the major horizons occur in some soil profiles. ● Some locations do not contain all soil horizons. Table 8 Master horizons of soil classification O-horizon • organic horizon • contains undecomposed organic debris or decomposed organic materials and humus A-horizon • surface horizon or topsoil • contains inorganic matter mixed with leached mineral E-horizon • subsurface horizon • eluviated zone that contains little or no organic matter B-horizon • subsoil • illuviated zone that contains materials leached from upper horizons G-horizon • usually wet and clayey texture, mottling may be present C-horizon • slightly weathered parent material R-horizon • unaltered parent material 60 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 3 Soil profiles ● Adult soil: ● significantly developed soil profile ● B-horizon contains clay silicate, or oxides (aluminium, manganese and iron) ● yellowish, reddish or dark in colour (except if parent material is high in white calcium carbonate) ● influenced by climate, vegetation and drainage. ● Young soil: ● minimal horizonation ● A-horizon forms directly above R-horizon ● parent material is the strongest influence. ● Wet or waterlogged soils: ● poorly drained ● rubber-like consistency ● shrinks, hardens and cracks into cubes when drying out. ● Eroded soils: ● topsoil has been removed by wind, water or gravitational creep ● B-horizon is often the top layer ● unable to sustain crop life. 4 A practical identification of topsoil and subsoil horizons ● Topsoil characteristics: ● it is the topmost layer ● does not contain rocks ● high proportion of organic matter ● good drainage. ● Subsoil characteristics: ● just beneath the topsoil ● low in organic matter ● lighter in colour and stickier ● adults soils are rich in oxides ● more compact ● highest nutrient content. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 61

Unit 8 XX Soil classification ● Soil classification = grouping soil with similar properties. ● Distinguishing properties indicate type of horizons present and degree of development. 1 The binomial soil classification system in South Africa There are two main categories or levels of soil classes: ● Soil forms: ● an upper or general level ● defined by a unique vertical sequence of horizons. ● There are 73 soil forms. ● Soil families: ● a lower and more specific level ● they share properties of the form ● they are diﬀerentiated within the form based on other properties. ● There are 404 soil families. ● Steps involved in binomial soil classification system: ● demarcate master horizons ● identify diagnostic horizons (subsections of master horizons) ● name a soil form ● identify distinguishing family marks ● identify soil family ● determine texture class of A-horizon and add it to the soil family name, e.g. ● sandy loam, loam. 2 Diagnostic horizons of topsoil and subsoil horizons Topsoil and subsoil horizons may be divided into further subsections: ● five for topsoil and 14 for subsoil. ● These are diﬀerentiated based on various soil properties. Table 9 Diagnostic topsoil horizons Organic O high organic matter content (>20%), black to dark brown colour, low bulk density, 20–30 cm depth; formed in wet areas Humic A dark-coloured, moderate organic carbon content, low base status, well-drained Vertic A dark coloured, high clay content, swell-shrink properties, visible slickensides; found in sub-humid or semi-arid areas, or under grasslands Melanic A dark-coloured when dry, strong structure that is not hard when dry, no slickensides Orthic A low in organic matter, thin layer, sometimes light coloured, very common 62 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 8 Table 10 Diagnostic subsoil horizons E horizon • position: second in sequence of diagnostic horizons; • grayish and lighter colour than horizons above and below it, elluvial horizon low in clay and oxides, sandy, low chemical reactivity G horizon • position: below a vertic-A, melanic-A, orthic A or E-horizons; • grey or bleached, saturated with water Red apedal B • red colour, weakly structured, no alluvial or Aeolian stratifications Yellow-brown • analogue of the red apedal B, but yellow or brown instead of red apedal B Red structured B • position: below orthic A-horizon; • red and uniform colour, better structure than red apedal B Soft plinthic B • reddish brown, yellowish brown or black mottled colour, grey colours due to gleying in the horizon or just below it, contains sesquioxides Hard plinthic B • position: below orthic-A, yellow-brown apedal B or E horizons; • indurated zone containing iron and manganese Prismacutanic B • position: below orthic A- or E-horizon; • abrupt transition with overlying horizon with respect to at least two of texture, structure and consistence; prismatic or columnar structure; colour either does not indicate wetness or vertical faces have continuous coatings of uniform, dark colour Pedocutanic B • position: below topsoil or E-horizon, or via a stone-line; • moderate to strongly developed sub-angular or angular blocky structure in the moist state, enriched with clay Lithocutanic B • created by in situ weathering of rock under topsoil, variegated zone Neocutanic B • composed of unconsolidated material Neocarbonate B • same as red apedal, yellow-brown apedal or neocutanic B-horizons except for calcium and/or magnesium carbonate Podzol B • enriched in organic matter and sesquioxides; no textural differentiation; • e.g. sandy parent materials under fynbos vegetation Podzol with placic • position: lower 100mm of podzol B-horizon; pan • freely drained or gleyed 3 The benefits of soil classification in agriculture ● Organise and facilitate knowledge about soils. ● Understand the relationship among diﬀerent soils. ● Establish groups or classes of soils for practical purposes. ● Predict the behaviour of diﬀerent soils. ● Identify the best uses of soils. ● Estimate agricultural productivity potential. ● Transfer information to similar soils in other locations. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 63

Unit 9 XX Soil colloids and soil acidity 1 Soil colloids ● They are very small particles of either organic or inorganic matter: ● determine physical and chemical properties ● carry an electrostatic charge ● = which is pH dependent. 1.1 Description and characteristics of inorganic soil colloids ● Inorganic colloids ● → account for the majority of soil colloids. ● There are three main types: ● Phyllosilicate clay minerals ● Non-crystalline silicate clays ● Oxides. 1.1.1 Phyllosilicate clay minerals ● Derived from silica → contain aluminium, magnesium and hydroxide. ● responsible for cracks in dry soil (due to mineral shrinkage) ● responsible for nutrient retention ● protects soil from weathering, e.g. ● 1:1 type (kaolinite = most important clay mineral) ● 2:1 type (montmorillonite). 1.1.2 Non-crystalline silicate clays ● Formed from volcanic ash deposits. ● amorphous ● receptive and fertile minerals, e.g. ● allophone and imogolite. 1.1.3 Oxides ● Also known as sesquioxides. ● → responsible for nutrient retention, e.g. ● iron and aluminium oxide clays ● hydrous oxides. 1.2 Differences between inorganic and organic colloids Comparison of inorganic and organic colloids is shown in Table 11 on the next page. 64 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 9 Table 11 Comparison of inorganic and organic colloids Inorganic colloids Organic colloids (also called humus) soils and clays (dispersed colloid) + water (dispers- minerals from prehistoric plants (dispersed solid) + ing substance) water (dispersing substance) net positive charge net negative charge (but contains + and – charged species) increase water and nutrient retention 1.3 Cation adsorption and cation exchange in soil Cation exchange is the exchange of a cation in the soil solution for another cation on the colloid surface. ● Acidic / acid-forming cations: e.g. ● hydrogen (H+), aluminium (Al3+) ● neither are plant nutrients. ● Basic / alkaline-forming cations: e.g. ● calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+) ● main positively charged crop nutrients. ● Clay particles (–) attract nutrients and non-nutrients (+). ● Organic matter (– and +) attracts cations (+) and anions (–). ● → prevents leaching of essential nutrients. ● Cation exchange capacity (CEC) is the ability of soil to exchange cations with a soil solution. ● Expressed in centi mol per kg (cmols (+) kg–1). ● Can be altered by addition of organic matter and liming of a soil, e.g. ● in acidic soils, Al3+ replaces Ca2+. 2 Soil acidity ● Most agricultural crops give better yields on soils that are not too acid or too alkaline. ● Many South African soils are acidic and must be treated. ● The pH scale is used to measure acidity or alkalinity, where pH = –log [H+]. ideal pH range battery acid vinegar for plant growth car wash caustic soda pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 more acid neutral more alkaline Figure 5 The pH scale © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 65

Unit 9 2.1 The concepts: soil acidity, active acidity and reserve acidity 2.1.1 Soil acidity In humid regions, rainfall exceeds evapotranspiration. ● Soils become acidic when basic cations (Ca2+, Na+, Mg2+ and K+) are leached from the soil by rainwater: ● basic cations are replaced by Al3+ ● → which is hydrolysed to form aluminium hydroxide (Al(OH)3) solids and hydrogen (H+) ions in solution. ● Ca2+ is normally the predominant exchangeable cation in soils. ● In highly weathered soils, Al3+ may become the dominant exchangeable cation. 2.1.2 Active acidity Active acidity ● = the concentration of H+ ions in soil and water mixture. ● Measured using a pH meter. ● Can be neutralised by application of lime to soil. 2.1.3 Reserve acidity Reserve acidity : ● = concentration of H+ ions attached to clay and organic matter and not dissolved in solution. ● Measured as buﬀer pH in a buﬀer solution. ● Estimates the resistance of soil to pH change. 2.2 Factors influencing or causing the soil acidification process Soil acidification ● = a natural phenomenon that occurs after leaching due to heavy rain or the uptake of plant nutrients by the crop. ● Causes of soil acidity: ● application of sulphur (forms sulphuric acid) ● atmospheric pollutants such as sulphur dioxide ● weathering of acidic parent material ● use of nitrogenous fertilisers and leaching of nitrate from ammonium-based fertilisers ● loss of exchangeable bases from the soil due to leaching and erosion ● decay of organic matter (produces organic acids). 66 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 9 2.3 The effects of soil acidity on crop production Soil pH aﬀects plant nutrient availability. Optimum pH range is typically 6–7,5. ● The main eﬀects of soil acidity on crop production are: ● toxic organic compounds are broken down by micro-organisms ● activity of bacteria responsible for nitrogen fixation decreases ● → thus lower production of the main plant nutrient nitrogen ● availability of aluminium and manganese increases ● → which can be toxic and restrict uptake of nutrients calcium and magnesium ● phosphorus (an essential plant nutrient) forms insoluble compounds with aluminium and iron and thus becomes unavailable. 2.4 Methods of preventing or controlling soil acidification ● Apply lime (CaCO3), called liming the soil, to neutralise active acidity: ● CO32– reacts with H+ ions (from H2O) ● eliminates toxic Al3+ and H+ ● produces CO2 gas. ● Apply fertilisers to improve soil fertility. ● Avoid acidifying fertilisers. ● Plant acid-tolerant perennial species. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 67

Unit 10 XX Soil alkalinity and soil salinity 1 The concept: soil alkalinity (predominant cations) Soil alkalinity refers to how alkaline a soil is. ● Alkaline soils have the following properties: ● pH level above 7,0 ● contain large amounts of calcium, sodium and magnesium (released by weathering) ● less soluble than acidic soil ● iron, manganese, and phosphorus levels are too low for plant growth ● water and essential nutrients cannot penetrate the soil easily ● found in arid and semi-arid regions. 2 The concepts: saline soils and sodic soils 2.1 Saline soils ● Contain an excess of soluble salts, e.g. ● sodium chloride (common table salt) and calcium sulphate (gypsum). ● ‘Chemical drought’ occurs: ● water moves out of the roots via osmosis when salt concentration in the soil solution exceeds the salt concentration inside the roots – ● high soil electrical conductivity ● rain washes out chlorine, while the sodium remains leading to sodic soils. 2.2 Sodic soils ● These are chlorine-washed soils that contains excess sodium: ● defined as a non-saline soil, i.e. contain low total salt levels ● → result in poor crop production and soil structure ● → cause clay soil particles to disperse and form hard, impenetrable crusts. 3 Characteristics of saline or white brack soils Defining characteristic = contain suﬃcient neutral soluble salts to adversely aﬀect crop growth: ● Salt precipitates on the soil surface. Usually: pH < 8,5 ● electrical conductivity > 4 dS/m ● sodium adsorption ratio or exchangeable sodium percentage > 13 ● sodium and chloride present in large quantities ● calcium and magnesium present in adequate quantities ● contains large amounts of gypsum (calcium sulphate) ● contains no soluble carbonates. ● → Uneven growth of crops. 68 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 10 Salinity can be measured. To measure: ● saturate soil with distilled water ● leave to settle overnight ● measure the water with an EC meter ● Expressed as EC (electrical conductivity) in deci-siemens per metre (dS/m) ● defined by EC > 4 dS/m. 4 Factors causing brackishness, soil alkalinity or saltiness ● These factors cause brackishness, soil alkalinity or saltiness: ● salty irrigation water ● soil parent material ● poorly drained soils ● inorganic or synthetic fertilisers ● dairy and beef animal manure ● compost made from animal manure ● field slope and drainage. 5 The effects of alkaline or brack on crop productivity Alkaline levels regulate the availability of vital nutrients and aﬀect the ability of crops to absorb nutrients. ● If alkaline levels are too high: ● crops may wilt or die (even if soil moisture content appears adequate) ● salts at the root zone make extraction of water by roots diﬃcult. 6 Methods to prevent or control soil alkalinity ● Monitor soil pH (take several soil samples in your field). ● Test irrigation water. ● Apply sulphur or gypsum. ● Do not over use compost and animal manure. ● Irrigate to leach salts in drier areas. ● Cover soil with mulch during summer months. ● Do not over lime soil. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 69

Unit 10 7 Reclamation of alkaline or brackish soils Alkaline or brackish soil usually has low nitrogen content and a reduced availability of plant nutrients. These can be addressed as follows: ● Identify the cause of alkalinity. ● Establish drainage with good quality water. ● Add organic matter to facilitate drainage. ● Add gypsum to reduce the pH. ● Adopt a ridges and furrow system of planting. Alkaline soils that contain a high proportion of calcium carbonate are called calcareous soils. ● Use these ways to reclaim calcareous soils: ● add sulphuric acid to leaching excess calcium carbonate ● add sulphur to form sulphuric acid in situ ● choose a salt-tolerant crop, e.g. barley. 70 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 11 XX Soil organic matter: Living organic matter Micro-organisms and macro-organisms make up the living organic matter of the soil. ● Micro-organisms are microscopic. ● Macro-organisms can be seen with the naked eye. ● they live mostly in the surface layers of the topsoil ● they break down non-living organic matter in the soil for re-use by plants. 1 Importance and role of soil micro- and macro-organisms The major role of soil organisms is to maintain the balance of the soil ecosystem and to provide plants with nutrients. ● Importance and role of soil micro-organisms: ● decompose dead plants and animals, and animal dung ● free nutrient elements from organic material for use by other organisms ● fix atmospheric nitrogen into soil ● improve soil structure ● help to form soil. ● importance and role of soil macro-organisms: ● decompose dead organic matter so that micro-organisms can decompose it further → provide food for other animals. 2 Main groups of soil micro-organisms 2.1 Bacteria Bacteria are vital in recycling nutrients. ● Many are anaerobic → so they release methane instead of CO . 2 ● Can be classified as autotrophic or heterotrophic: ● autotrophic bacteria: use carbon for food ● → do this by extracting CO2 from air and using sunlight or nitrogen and sulphur for energy. ● heterotrophic bacteria: decompose dead organic matter, recycle nutrients and release CO2 into the air ● Bacteria involved in decomposition of organic matter can be classified according to the temperatures at which they grow best, i.e. ● psychcrophilic, mesophilic and thermophilic (order of increased temperature preference) ● Photosynthetic bacteria: ● use sunlight for energy, e.g. blue-green or cyanobacteria. ● some are nitrogen fixers, e.g. Azotobacter. ● Nitrifying and denitrifying bacteria: ● → convert nitrogen compounds into diﬀerent forms. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 71

Unit 11 XX 2.2 Other micro-organisms 2.2.1 Fungi ● They produce long thin branches (hyphae): ● → form a network (mycelium) which infiltrates the tissue of plants or animals. One group is called mycorrhizae: ● exhibit symbiosis with almost all plant roots ● aid nutrient exchange ● increase disease and drought resistance. 2.2.2 Algae ● They are single-celled organisms that contain chlorophyll: ● → allows them to photosynthesise. ● They are dependent on high levels of moisture. ● Some fix nitrogen from the air into the soil in the form of ammonia. 2.2.3 Protozoa ● They are single-celled organisms that live in moist soil: ● metabolise by photosynthesis ● prey on bacteria, fungi and nematodes. 3 Main groups of soil macro-organisms 3.1 Annelids ● Example of annelid = earthworms: ● swallow and digest dead organic matter ● excrete digested products in casts or dung in the lower subsoil ● micro-organisms break down the semi-digested products. 3.2 Molluscs ● Examples of mollusc = snails and slugs (species called gastropods): ● eat live plants and dead plant matter ● assist in the breakdown of organic matter. 3.3 Arthropods ● Examples of arthropods = flies (insects), woodlice (isopods), mites (arachnids), centipedes (myriapods): ● creatures with jointed legs or segmented bodies ● eat dead organic matter and decompose into smaller pieces for micro-organisms ● feed on plant-eating soil organisms ● dung beetles and termites are found in dry soils. 72 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 11 3.4 Nematode worms ● Nematode worms = very small. ● millions found in the upper layers of the soil ● eat and decompose rotting flesh of plant matter. 4 Requirements for soil micro- and macro-organisms Table 11 Requirements for soil micro- and macro-organisms Micro-organisms Macro-organisms Moisture water required for their metabolism, soil moist soil because many can dry out easily must contain 50–80% moisture Temperature optimal range is 25–30 oC Light required by photosynthetic organisms protection from sunlight pH optimal range is 6–8 Air mostly aerobic organisms Food main nutrients = carbon, nitrogen dead organic matter minor nutrients = calcium, phosphorus, potassium 5 The carbon cycle and conversion by soil micro- organisms ● Six main steps in the cycle: ● Step 1: plants extract CO2 from the air during photosynthesis. ● Step 2: plants make sugars, starches and cellulose. ● Step 3: plant products are ingested by herbivores. ● Step 4: micro-organisms decompose dung or dead bodies of herbivores. ● Step 5: micro-organisms release CO2 into the air. ● Step 6: CO2 is used by plants. ● Plants and animals also release CO2 during respiration. 6 The nitrogen cycle and conversion by soil micro- organisms ● Ammonifying organisms: protein / urea → NH4+: ● bacteria and fungi decompose proteins or urea from plant and animal matter ● ammonium is released into the soil ● ammonification or mineralisation: chemical compounds in organic matter are made available to plants for nutrition ● immobilisation: organic matter decomposes and is absorbed by micro- organisms, therefore becoming unavailable to plants. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 73

Unit 11 XX ● Nitrifying bacteria, Nitrosomas: NH4+ → NO2 (i.e. converts ammonium to nitrites): ● process called nitrification ● nitrites are toxic to plants, but are rapidly converted to nitrates. ● Nitrifying bacteria, Nitrobacter: NO2 → NO3 (i.e. converts nitrites to nitrates): ● nitrates can be used by plants. ● Nitrogen-fixing organisms: ● absorb and fix nitrogen from the air into plants or the environment ● use an enzyme called nitrogenase ● → called nitrogen assimilation ● symbiotic nitrogen fixers: bacteria found in root nodules of legume plants, e.g. ● Rhizobium ● non-symbiotic fixers: free-living micro-organisms, e.g. ● Azobacter ● Denitrification bacteria: N2 → NO (i.e. converts nitrogen to nitrous oxide): ● process called volatilisation. 7 The phosphorus cycle ● Three main steps in the cycle: ● Step 1: plants absorb phosphorus from soil WHEREAS animals obtain phosphorus by eating plants. ● Step 2: plant and animal matter are decomposed by micro-organisms. ● Step 3: micro-organisms release phosphorus into the soil (i.e. mineralisation). ● Most phosphorus is unavailable as it is insoluble or bound to soil particles. ● Micro-organisms release some of this insoluble phosphorus (i.e. solubilisation). 8 The process of symbiosis ● Symbiosis = co-operation between two diﬀerent organisms which benefits both organisms. ● Symbiotic relationships occur between plants and soil micro-organisms. ● Mycorrhizae as an example: ● fungi species that attach to plant roots ● plant benefits by increased absorption of phosphorus ● fungus obtains carbon and other growth requirements from the plant. ● Rhizobium bacteria as an example: ● penetrates the roots and forms nodules in the tissues ● plant receives nitrogen extracted from the air ● bacteria receives water and nutrients from the host plant ● symbiosis is reduced by nitrogen fertilisation, high soil acidity and temperatures. 74 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 12 XX Soil organic matter: Non-living organic matter 1 Definitions of fresh organic matter and humus Fresh organic matter: ● = Dead remains of living plants and animals. ● Components decompose at diﬀerent rates. ● To accelerate decomposition you should: ● provide aeration and moisture ● ensure the correct pH ● correct the carbon:nitrogen ratio ● add nitrogen-containing compounds ● Fresh organic matter → not suitable for use as compost. Humus: ● = Final product of decomposition of fresh organic matter: ● dark and crumbly ● smells like soil. 2 Effects of organic matter on soils ● Physical eﬀects: ● improves soil structure of soil (by causing aggregation of particles) ● improves drainage of clay soils ● binds sandy soil, which lessens damage by water and wind erosion ● improves aeration ● humus increases soil temperature which favours plant growth. ● Chemical eﬀects: ● provides basic nutrients ● prevents leaching of nutrients ● produces organic acids which aid weathering. ● Biological eﬀects: ● creates favourable conditions for micro- and macro-organisms ● organisms promote aeration and nutrient recycling. 3 Factors that affect the balance of organic matter in soils The factors that aﬀect the balance of organic matter in soils are summarised in Table 13 on the next page. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 75

Unit 12 XX Table 13 Factors that affect the balance of organic matter in soils Gains Losses Nature • falling leaves and dead grass • microbial decomposition • animal dung deposits • wind and water erosion • dead roots • high moisture and temperature Agriculture • compost or organic fertilisers • tillage and cropping methods: • shallow tillage methods • increase wind and water erosion • bury and putrefy crop residue • compaction by heavy equipment 3.1 Impact of decomposition of organic matter on global warming ● Decomposition by aerobic micro-organisms → release of carbon dioxide (CO2). ● Decomposition by anaerobic micro-organisms → release of methane (CH4). ● Methane contributes much more to global warming then carbon dioxide. ● Burying organic matter in landfills contributes to global warming. ● Composting kitchen waste is preferable and returns organic matter to soil. 4 Effects of the decline in organic matter on soil degradation ● Although inorganic fertilisers add nutrients to soil they do not improve soil quality: ● soil becomes drier ● more compact ● less well aerated ● nutrients are leached. 5 Making a compost heap ● Select a site. ● Dig a trench and fork the base. ● Line the base with sticks or branches. ● Layer the heap: ● first carbon-containing browns ● then nitrogen-containing greens ● use more brown than green matter ● should be 750 cm wide and 250 cm high ● repeat layering monthly for three months ● Keep moist. It is ready when you have dark, flaky, sweet-smelling humus. 76 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Topic 2 Unit X XX Topic questions ● Answer the questions below. ● Give yourself one hour. ● Check your answers afterwards and do corrections. 1 Name and describe the 3 main groups of soil particles with respect to their size. (6) 2 Describe three factors that influence the development and stability of soil structure. (6) 3 Soil colour is influenced by the amount of organic matter, the presence of various compounds, drainage and leaching. Explain three of these factors with examples and colours. (6) 4 Name the three main soil gases and state which one is the most important for plant growth and development. (4) 5 Answer the following questions about soil moisture. a Name three types of soil water. (3) b Ascribe each of these properties to one of the 3 types of soil water. i found in soil macro pores ii held on particle surface by adhesion forces iii found in soil micro pores iv not available to plants because held tightly by roots v held against pull of gravity. (5) c Fill in the missing word: Soil water content is a function of water supply and water _______. (1) d Name four factors that contribute to the missing word provided in (c) above. (4) 6 One of the main factors influencing soil temperature is soil cover. a Explain (3) b State one way in which this can be measured. (1) 7 Briefly compare topsoil and subsoil. (4) 8 Name the system used to classify soils and list three benefits of soil classification in agriculture. (4) 9 Explain the term ‘soil colloid’ and give two examples. (4) 10 Explain the diﬀerence between active acidity and reserve acidity. (2) 11 State four methods to prevent or control soil alkalinity. (4) 12 Describe the phosphorus cycle and include the terms mineralisation and solubilisation in your answer. (6) 13 Explain the symbiotic relationship between Rhizobium bacteria and plants. (3) 14 Explain how the decomposition of organic matter can influence global warming. (4) Total: 70 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 77

X 3 Topic XX Unit Plant studies Overview • Photosynthesis and respiration UNIT 1 Page 80 • Pigment and photosynthesis Plant nutrition and • Light and dark phases of photosynthesis photosynthesis • Food storage in plants • Rate of photosynthesis • The importance and functions of water in plants UNIT 2 Page 84 • The movement of water from the soil to the roots of plants Water and nutrients • Osmosis and diﬀusion in plant cells • Movement of water in plants and into the atmosphere • Adaptation of plants to reduce transpiration rate • Movement of the products of photosynthesis UNIT 3 Page 87 • An introduction to macro- and micro-elements Mineral nutrition • The diﬀerent macro-elements • The diﬀerent micro-elements TOPIC 3 Page 78 UNIT 4 Page 91 • Types of plant nutrient or mineral uptake • Forms in which nutrients or minerals are available to plants Plant studies Plant nutrient uptake • Factors aﬀecting the availability of nutrients to plants and analysis • Importance of nutrient element analysis in crop production • Methods to determine nutritional status of soil UNIT 5 Page 94 • An introduction to fertilisers Organic and inorganic • The main inorganic fertilisers and their impact on the fertilisers environment • Agricultural lime • The use of gypsum UNIT 6 Page 98 • Main types of organic fertilisers • The concept: green manure Organic fertilisers and • Description of farm manure fertilisation practices • Description of compost • Fertilisation practices UNIT 7 Page 101 • Sexual reproduction in plants Plant reproduction: • Fertilisation process in plants Sexual reproduction • Seeds and fruit setting • Seed germination 78 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

X 3 Topic XX Unit Plant studies Overview UNIT 8 Page 108 • Types of asexual methods of reproduction Plant reproduction: • Oculation and grafting Asexual reproduction • Advantages and disadvantages of asexual plant propagation methods UNIT 9 Page 115 • Plant improvement Plant improvement and • Biotechnology biotechnology TOPIC 3 Page 78 Plant studies UNIT 10 Page 118 • Weeds and herbicides • The impact of weeds on agriculture Weed management • Features of weeds that make them successful control • Agents of weed dispersion or transmission • Methods of weed control UNIT 11 Page 123 • Plant diseases and their control • Pesticides, plant pests and their control Plant diseases and pest • Integrated pest management (IPM) control • Insect control in stored seed and grass • Plant protection and the state © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 79

Unit 1 XX Plant nutrition and photosynthesis 1 Photosynthesis and respiration 1.1 Photosynthesis ● Converts light energy into the chemical energy of sugars and other organic compounds, i.e. ● CO2 + H2O + energy sun → carbohydrates + O2 ● chemical energy is stored in the form of glucose (a carbohydrate) ● secondary products: other carbohydrates, lipids, proteins. ● Photosynthesis process occurs mainly within the leaves: ● CO2 is obtained through stomata ● H2O is obtained through the roots ● sunlight is absorbed by chlorophyll located in chloroplasts – site of photosynthesis ● O2 is released through stomata. ● Importance of photosynthesis: ● production and renewal of almost all the atmospheric oxygen ● provision of food for all plants and animals ● production of fossil fuels (coal, natural gas and oil) from plant and animal remains ● reduction of CO2 in the atmosphere. ● Energy produced is used in respiration. 1.2 Respiration ● Plants and animals break down energy-rich organic compounds into simple inorganic compounds ● = release large amounts of energy for cellular work necessary for growth and reproduction, i.e. ● carbohydrates + O2 → CO2 + H2O + chemical energy. Table 1 The differences between photosynthesis and respiration Photosynthesis Respiration • produces food • consumes food • stores energy • releases energy • consumes H2O • produces H2O • consumes CO2 • produces CO2 • releases O2 • consumes O2 • light-dependent • light-independent 80 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 2 Pigment and photosynthesis ● Pigments absorb light energy and provide energy. Main groups of pigments = ● chlorophylls (provide green colour) ● and carotenoids (provide yellow, orange or red colour). ● Chlorophyll pigments: ● found in chloroplasts ● trap energy from sun which supplies energy for photosynthesis ● helps plants to form products needed for growth during photosynthesis ● composed of central magnesium atom surrounded by several nitrogen- containing hydrocarbon rings with long hydrocarbon tails. 3 Light and dark phases of photosynthesis Photosynthesis takes place in two phases: the light (or light-dependent) phase and the dark (light-independent) phase. ● Light phase: ● occurs in the thylakoid membranes of the chloroplast ● light energy → energy carried by electrons ● energy in the electrons is used to make ATP (energy carrying compound) and NADPH which are used for the next main step ● oxygen is a by-product. ● Dark phase (or Calvin cycle): ● occurs in the stroma of the chloroplast ● controlled by enzymes (therefore aﬀected by temperature) ● CO2 is first incorporated into RuBP (ribulose biphosphate) ● hydrogen and electrons from NADPH are added to form GP3 or PGAL (carbohydrate) ● PGAL is used to make glucose and other carbohydrates for the plant. 4 Food storage in plants ● Plants store excess energy, nutrients or water in storage organs for future growth: ● insoluble products take up less space ● excess products are made insoluble by dehydration and hydrolysis reactions ● temporary storage of starch occurs in leaf cells during the day. ● Food storage organs often grow underground as they are protected from herbivores: ● storage organs = ● roots / tubers / bulbs (e.g. carrots, radish) ● stems (e.g. potato, sugarcane) ● leaves (e.g. onion, lettuce) ● seeds (e.g. peas, maize) ● fruit (e.g. tomatoes, pecan nuts). © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 81

Unit 1 5 Rate of photosynthesis It is the rate of O2 production per unit mass (or area) of green plant tissues or per unit weight of total chlorophyll. 5.1 Factors affecting the rate of photosynthesis 5.1.1 Temperature ● Temperature = directly proportional to rate of photosynthesis and respiration: ● photosynthesis reaches a maximum rate, which varies with diﬀerent plant species ● optimum temperature = temperature at which growth is the fastest ● lower lethal temperature = temperature below which cells are killed. ● Farmers should choose plants according to area, season and time. photosynthesis Rate respiration minimum optimum maximum growth growth growth temperature temperature temperature Figure 1 Rate of photosynthesis and respiration vs. temperature 5.1.2 Light ● Light = directly proportional to rate of photosynthesis (until optimum light intensity reached): ● plant species diﬀer in their optimum intensities ● few crop plants grow well in shade ● exception = sweet potatoes. 5.1.3 Carbon dioxide ● Carbon dioxide = directly proportional to rate of photosynthesis: ● light and water must also be available. 5.1.4 Water ● Water → required for photosynthesis and transpiration: ● shortage of water → causes growth to slow down or stop. 82 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 5.2 Manipulation of plants conditions to increase photosynthetic rate ● Temperature: ● ensure enzymes have an optimal temperature range. ● Nutrients: ● ensure that plants have optimum nutrients. ● Light: ● increase light intensity under which crops grow ● manipulate light colour in growing environment (chlorophyll absorbs red and blue light and reflects green, orange, and yellow light) ● increase exposure time to light. ● CO2 concentration: ● increase CO2 availability by adding KHCO3 or NaHCO3 to the water. ● Water: ● insuﬃcient water ● → the plant’s stomata will shut ● → deprive plant of CO2. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 83

Unit 2 XX Water and nutrients 1 The importance and functions of water in plants ● Seed germination: mature seeds are dry and need water for metabolism and growth. ● Plant growth: cell division and expansion require water: ● → lack of water minimises growth of new shoots and leaves, thus less sugar available for fruit growth ● Nutrient transport: mineral nutrients dissolve in soil water and are absorbed through roots. ● Photosynthesis: process whereby plants produce their food → requires water. ● Stomata: water content of guard cells determines whether they open or close stomata. ● Plant structure: water pressure in cells (turgor pressure) helps maintain their shape. ● Plant habitats: watery environments support aquatic plants, e.g. sea, rivers. 2 The movement of water from the soil to the roots of plants ● Roots draw up water and nutrients from the soil. ● Root hairs provide a large surface area for absorption. ● Water molecules containing mineral salts pass from the soil through the thin cell walls of the roots into the plant by osmosis: ● mineral concentration is higher inside root cells than in the soil ● → this creates root pressure (type of osmotic pressure) ● this pressure forces water up, out of the root. 3 Osmosis and diffusion in plant cells ● Osmosis: ● passage of water through a semi-permeable membrane ● driven by osmotic pressure, i.e. tendency of pure solvent to move through semi-permeable membrane into solution with solute to which membrane is impermeable. ● Diﬀusion: ● molecules spread from an area of high concentration to one of low concentration until an equilibrium is reached Both processes involve movement of molecules down a concentration gradient (i.e. high to low) and do not require an external force. 84 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 4 Movement of water in plants and into the atmosphere 4.1 Movement of water from the roots to the stems and leaves 4.1.1 Osmotic flow and root pressure ● Water enters the roots by osmosis: ● flow of water, called osmotic flow, is driven by a concentration gradient ● water diﬀuses from root hairs to the xylem of the root, where sap is more concentrated than soil water ● pushes existing water up the plant = called root pressure ● → water moves up through the xylem of the root and stem. ● BUT root pressure is not strong enough to move water very high up ● → use transpiration pull. 4.1.2 Transpiration pull ● Driven by transpiration rate, facilitated by cohesion of hydrogen bonded water molecules: ● water is lost through the stomata of leaves by transpiration ● pulls up entire column of water into the petiole (leaf stalk) and plant leaves ● uses capillary action (or capillarity). 4.2 Movement of water from the leaf to the air 4.2.1 Transpiration ● Transpiration = the evaporation of water from surface of plant leaves: ● the sun warms water inside leaves and it changes to water vapour ● vapour diﬀuses through the stomata (controlled by guard cells) ● → allows mass flow of plant nutrition and water from roots to shoot. 4.2.2 Guttation ● Guttation = loss of water in liquid form from an uninjured leaf or stem: ● occurs when pressure builds up in leaves at night due to lack of transpiration. 5 Adaptation of plants to reduce transpiration rate 5.1 Stomata (main adaptation) ● Stomata = tiny passages that allow exchange of gases between plant and atmosphere: ● surrounded by guard cells that control whether stomata open or close ● function of guard cells depends on their water pressure (turgor pressure) – ● if full of water, stoma open (allow diﬀusion of CO2) ● BUT if they lose water, then stoma close. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 85

Unit 2 ● Stomata maintain a fine balance to ensure eﬃcient photosynthesis but prevent dehydration, e.g. ● usually open during daylight, respond to temperature and wind. 5.2 Special plant adaptations ● Xerophytes, e.g. succulents ● during the day stomata close to retain water ● at night, stomata open when water loss by transpiration is lower and CO2 enters and is stored for use during daylight ● leaves rolled inwards to conceal stomata. 5.3 Leaf adaptations ● Fewer or sunken stomata. ● Tiny or needle-shaped leaves reduce surface area. ● Thickness and size diﬀer depending on whether in shade or sunlight. ● Shiny or waxy surfaces, covered in fine hairs, thick cuticles. 6 Movement of the products of photosynthesis ● Photosynthesis products are called photosynthates, e.g. ● sugars, amino acids, fatty acids. ● Photosynthates = moved from where they are made (the source) to where needed (the sink) via the phloem: ● pressure gradient between source and sink drives sap along the phloem tubes. ● Source: cells load photosynthates into the phloem ● → water moves in from xylem ducts by osmosis ● → sap pushed along the phloem (called translocation). ● Sink: photosynthates transported out the phloem ● → sugars consumed or converted into starch. 86 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 XX Mineral nutrition 1 An introduction to macro- and micro-elements This schematic shows the diﬀerent types of element found in soil with examples of each. * Elements / nutrients in soil Micro-/ trace elements Macro-elements Fe, Cl, Mn, Zn, B, Cu, Mo major elements minor elements N, K, P Ca, Mg, S * Other essential elements for normal growth: C, H, O – found in air and water ● Macro-elements: required for plants to thrive → used in relatively large amounts (the same definition applies to major elements). ● Micro-elements: not needed as much as macro-elements → used in smaller amounts (the same definition applies to minor elements). ● Form(s) in which elements are taken up by plants: ● Major elements: N as NH4+, NO3–; K as K+; P as H2PO4–, HPO42– ● Minor elements: Ca as Ca2+, Mg as Mg2+, S as SO42– ● Micro-elements: Fe as Fe2+, Fe3+; Cl as Cl–; Mn as Mn2+; Zn as Zn2+; B as H3BO3–, Cu as Cu2+ and Cu3+; Mo as MoO42–. 2 The different macro-elements Table 2 Major macro-elements Nitrogen (N) Phosphorus (P) Potassium (K) Uses • constituent of • constituent of proteins, • regulates flow of soil water; proteins, nucleic nucleotides, phospholipids, and • catalyses reactions for: enzyme acids, hormones, ATP; activation, protein synthesis, starch co-enzymes and • thus: promotes cell division, synthesis and translocation, nitrate chlorophyll; shortens growth period, improves translocation, control of stomata; • promotes vegetative fertility and seed production, • efficient photosynthesis thus: growth (by changing improves nutrient value and improved yield and disease- carbohydrates to disease-resistance of crops, resistance of crops; proteins) improves keeping properties of • development of root system fruit, vegetables and cereals © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 87

Unit 3 Table 2 Major macro-elements Nitrogen (N) Phosphorus (P) Potassium (K) Forms • major form: NO3– in • inorganic: H2PO4– (major form) • K+ ions from soil water soil water; • organic: absorbed as phytin, • NH4+ also in soil phospholipids and nucleic acids water; (not usually natural) • urea converted to NH4+ and used as foliar feed Symptoms of deficiency • stunted growth; • purple, discoloured leaves; • leaf scorch • yellowing of older • reduced: growth, flower, seed leaves; and fruit production, nutrient • leaves become brown value, keeping quality or die (severe) Symptoms of toxicity • result of excess NH4 ;+ • early ripening / excess crops; • acidic and sour citrus fruit; • crops and cereals • small fruit spoil quickly; • scorched leaf tips become excessively • scorched leaf tips; succulent; • leaves become yellow • poor quality fruit; • falling or scorched leaves Table 3 Minor macro-elements Magnesium (Mg) Calcium (Ca) Sulphur (S) Uses • constituent of • stabilise membrane structure; • constituent of two amino acids and chlorophyll; • makes cell walls rigid; some vitamins; • activates enzymes • required for activation of some • activation of certain enzymes for carbohydrate and enzymes; protein metabolism; • development of growth tips and • with sulphur, roots increases rate of lipid synthesis Forms • Mg ions in soil 2+ • Ca in soil water; 2+ • SO42- ions in soil water water; • bonemeal, lime and gypsum • MgSO4 (Epsom salts) contain Ca (applied to soil) and dolomitic lime supplements Symptoms of deficiency • chlorosis • leaves chlorotic and curled; • slender plants; • stunted plant; • yellowing leaves; • poorly developed roots; • decreased growth rate • poor nutrient uptake Symptoms of toxicity • never seen under • rarely seen; • unlikely; natural conditions • insoluble phosphate salts form, • scorched edge in older leaves thus P deficiency 88 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 3 The different micro-elements Table 4 Properties of the trace element, iron (Fe) Uses Forms Deficiency and toxicity • component of electron • soluble iron salts in soil Deficiency: transport proteins; water (e.g. FeSO4); • occurs on calcareous soils - insoluble • needed for chlorophyll • iron chelate in foliar spray iron salts precipitate at high pH; formation • susceptibility varies between plants; • starts in young leaves which show interveinal chlorosis; Toxicity: • none in natural conditions Table 5 Properties of the trace element, manganese (Mn) Uses Forms Deficiency and toxicity • required for • Mn2+ in soil water; Deficiency: photosynthesis; • Mn2+ in foliar spray • young leaves are chlorotic, woody • co-factor in respiration stems; brown necrotic spots in middle and N metabolism of legume seeds; Toxicity: • only due to poor fertilisation practices Table 6 Properties of the trace element, copper (Co) Uses Forms Deficiency and toxicity • constituent of electron • Cu in soil water; 2+ Deficiency: transport proteins, • CuSO4 solutions as foliar • similar to chlorosis; enzymes that catalyse spray • young maize leaves yellow, stunted; respiration reactions • reduced growth in apples; Toxicity: • rare in plants Table 7 Properties of the trace element, zinc (Zn) Uses Forms Deficiency and toxicity • activation of various • Zn2+ ions in soil water; Deficiency: enzymes (main function); • Zn2+ as a foliar spray • maize: chlorosis, reduced growth, • synthesis of a precursor of brownish-purple stripes on stem; auxins (plant hormones) • fruit trees: lower leaves are small, light, curled edges; Toxicity: • severe stunting, interveinal chlorosis © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 89

Unit 3 Table 8 Properties of the trace element, molybdenum (Mo) Uses Forms Deficiency and toxicity • component of enzyme • MoO42– in soil water; Deficiency: that converts nitrates to • sodium molybdate as • interveinal chlorosis; nitrites; foliar spray • cabbage family: tall, slender plants • essential for nitrogen Toxicity: fixation by bacteria • rare unless excessive Mo spraying Table 9 Properties of the trace element, boron (B) Uses Forms Deficiency and toxicity • aids sugar translocation • H3BO3 in soil water; Deficiency: during carbohydrate • borax as a supplement • apples and tomatoes: internal cork; metabolism; • root crops: brown or black heart; • influences nucleic acid • celery: stem-crack occurs; cell content at growth tips • multiple small new stems form; of roots and stems Toxicity: • N and B most common toxicity due to poor fertilisation practices; • stunted plants Table 10 Properties of the trace element, cobalt (Co) Uses Forms Deficiency and toxicity • role as essential micro- none Deficiency: nutrient has not been • none in plants, grazing stock show established evidence of wasting disease or pining Toxicity: • rare in grazing fields; • tomatoes: chlorosis, very dark green or deformed leaves 90 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 XX Plant nutrient uptake and analysis 1 Types of plant nutrient or mineral uptake 1.1 Passive ion uptake ● Nutrient elements diﬀuse from soil water into the root down the concentration gradient: ● requires no energy ● i.e. = passive ● rate depends on steepness of concentration gradient. 1.2 Active ion uptake ● Absorbs nutrient elements from soil water against concentration gradient: ● requires energy ● i.e. = active ● carried out by transport carrier molecules that supply this energy (i.e. ATP) ● → ATP binds the nutrient and transports it one-way across the membrane. 2 Forms in which nutrients or minerals are available to plants Table 11 Nutrient forms of phosphorus, potassium and nitrogen Phosphorus (P) Potassium (K) Nitrogen (N) Organic: Ca2+ bound as mono-, total K content high but most Gas: unavailable directly di- (available) or tricalcium unavailable to plants; except in legume family that phosphates (unavailable); SA equilibrium between different uses Rhizobium nitrogen-fixing has little but available from types of potassium bacteria nucleic acids, phospholipids, Soluble K: in salts KCl and K2SO4 Organic: main N source; from phytin (available) manure, compost, fertilisers Inorganic: bound in iron or Fixed K: fixed by some clay (available after decomposition by aluminium compounds – called minerals (available) microbes) fixed phosphates (unavailable) Adsorbed K: adsorbed to negative Ammonium (NH4+): end product charge on clay particle (available) of protein decomposition K in rock minerals: unavailable (available); but reserve (after soil-forming adsorption to clay colloids processes) prevents leaching Nitrates (NO3–): major form absorbed (available); does not adsorb to soil colloids, thus some leaching © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 91

Unit 4 3 Factors affecting the availability of nutrients to plants ● Soil pH. ● Presence of other nutrients. ● Leaching: leads to draining of mineral salts from the topsoil to subsoil where unavailable. ● Crop removal: clean clearing, deforestation or cutting down of harvested crops. ● Oxidation and reduction: changes state of mineral salts, thus salts may be washed away. ● Burning: reduces plant nutrients. ● Erosion: removes soil nutrients. Table 12 Factors affecting availability of P, K and N to plants Phosphorus (P) Potassium (K) Nitrogen (N) Soil pH: determines form of Alternative dying out and Application of organic matter: P thus availability; H2PO4– is wetting of soil: clay minerals improves nitrogen content; initially preferred ionic form fix potassium when soil dries ammonium and nitrates used by moisture content: determines out microbes (i.e. nitrogen negative amount that can dissolve in Other elements in the soil: period); microbes multiply and die, soil water excess calcium causes K releasing nitrogen back into soil Activity of micro-organisms in exchange on clay surfaces, Soil air: aerobic bacteria that organic matter: use inorganic increasing K content of decompose organic matter need well P (decrease availability); soil water (available but aerated soil produce organic acids and susceptible to leaching) Moisture content: aerobic soil decay products (increase Type of clay mineral: some clay microbes need water to function, availability) minerals have high adsorption but excess water prevents them Other elements in the soil: capacity, thus low potassium receiving O2 excess calcium forms are availability Soil type and soil pH: influence unavailable Ca3(PO4)2 microbe activity Other factors detrimental to soil microbes: high salinity, disinfectants and poisonous substances 4 Importance of nutrient element analysis in crop production ● Well managed nutrient levels help achieve profitable yields: ● → farmers should conduct soil nutrient element analysis to determine additional nutrients required for optimum crop production. Common terms used to describe nutrient levels: ● deficient: low concentration that severely limits yield ● insuﬃcient: level below that required for optimum yields, symptoms seldom evident ● suﬃcient: adequate levels for optimum crop growth ● excessive: level high enough to cause shortage of another nutrient ● toxic: levels high enough to reduce plant growth or cause death of plants 92 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 5 Methods to determine nutritional status of soil 5.1 Soil sample analysis ● Soil sample analysis = usually done before planting: ● contact analytical laboratory for questionnaires and packets ● keep samples for each land unit, and topsoil (10) and subsoil (5) separate ● draw representative sample from mixed sub-samples ● place in clean bag (plastic, cloth or hessian), identify and deliver with questionnaire. 5.2 Plant or leaf sample analysis ● Plant or leaf sample analysis = done when crop is already growing: ● leaf sample taken to laboratory where it is washed, dried and stored ● representative sample taken at a certain time of the year ● pick 10–20 young, mature healthy leaves (at least 10 undamaged) before 10:00 ● do not wash, place in clean plastic bag and deliver to laboratory immediately. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 93

Unit 5 XX Organic and inorganic fertilisers 1 An introduction to fertilisers ● Fertiliser = organic or inorganic material of natural or synthetic origin (other than liming materials) that is added to soil to supply plant nutrients: ● six macro-nutrients: N, P, K, Ca, Mg, and S ● seven micro-nutrients: B, Cl, Cu, Fe, Mn, Mo, and Zn. ● Organic fertilisers = composed of decayed organic matter ● → broken down into humus by micro-organisms and soil animals. ● Inorganic fertilisers = chemical preparations consisting of inorganic salts applied to soil or directly to plants ● → referred to as artificial or commercial fertilisers. 2 The main inorganic fertilisers and their impact on the environment 2.1 Nitrogenous fertilisers They usually contain the words ‘ammonium’ or ‘nitrate’ or ‘urea’ in their names. Table 13 Main types of nitrogenous fertilisers Urea, CO(NH2)2 Limestone ammonium nitrate Ammonium sulphate, (NH4)2SO4 (LAN), CaCO3NH4NO3 contains highest nitrogen mixture of CaCO3 and NH4NO3; contains 21% nitrogen as NH4+, content of 46%; released in the nitrogen supplied by NO3– and and 24% sulphur as SO42– form of NH4+ by hydrolysis NH4+ (80% of LAN) consists of regular, round, white consists of large, irregular, grey- granules that are water soluble; white granules that are water NH4+ adsorbed to soil colloids soluble; and released slowly, not readily NH4+ adsorbed to clay colloids, leached not readily leached except when oxidised to NO3–; NO3– immediately available but easily leached uses: replenish nitrogen, as uses: replenish nitrogen at uses: common as fertiliser: foliar spray, in irrigation water planting time and as a top- sulphate reduces pH, release dressing, and on acid, sandy of NH4+ forms acid which also soils (CaCO3 increases pH) lowers pH 94 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 2.2 Phosphorus fertilisers 2.2.1 Rock phosphate (or Langfos) ● Raw phosphate found in basic slag and rock phosphate. ● Basic slag ● → contains 9,5% phosphorus, fine dark grey powder, readily available, no leaching, good residual eﬀect, must be ploughed deep into soil before seeding and planting. ● Rock phosphate ● → contains 12% phosphorus, fine yellow powder, not readily available, no leaching, slow uptake, cheap, must be ploughed deep into soil before seeding and planting, used in acid soil to supplement phosphorus. 2.2.2 Superphosphate (monocalcium phosphate, Ca(H2PO4)2) ● Most popular fertiliser for supplying readily available phosphate: ● whitish-grey granular fertiliser ● contains 11,3% phosphorus ● readily soluble and available ● usually contain 50% gypsum (to prevent consequent sulphur deficiency) ● soon precipitates with calcium, not easily leached, less available to plants ● used to supplement phosphorus at or before planting. 2.3 Potassium fertilisers They typically contain the words ‘potash’ or ‘potassium’ in their names. Table 14 Types of potassium fertilisers Potassium chloride, KCl Potassium sulphate, K2SO4 • contains 50% potassium • contains 40% potassium • uses: for crops which do not tolerate KCl, supplement K where KCl unsuitable due to high chloride soil content • white salt • white salt • water soluble, immediately available, adsorbed • water soluble, immediately available, adsorbed to soil colloids thus not leached to soil colloids thus not leached 2.4 Mixed or compound fertilisers ● Mixture of nitrogen (N), phosphorous (P) and potassium (K): ● also contain other minerals, e.g. ● sulphur (S). ● Each type is designated by a number, e.g. ● 2:3:2 (24) means the ratio of N to P to K is 2:3:2 and 24 kg out of 100 kg are minerals. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 95

Unit 5 Calculation of the percentage plant nutrient in mixed fertilisers Example: Calculate the percentage of nitrogen in the fertiliser mixture 2:3:2 (24). Answer: ● The total quantity of all three nutrients together in 100 kg of the mixture is 24 kg. ● The sum of the parts of each nutrient is 2 + 3 + 2 = 7. ● Mass of N in 100 kg mixture = 2⁄7 of 24 = 6,8 kg or 6,8% 2.5 Impact of inorganic fertilisers on the environment ● Environment negatively aﬀected when fossil fuels are burned during their production: ● release substances that contribute to acid rain and greenhouse eﬀect ● cause water contamination ● does not add any organic material into the soil, thus organic material is depleted by soil micro-organisms ● contain sulphuric acid and hydrochloric acid which increase soil acidity, thus decreasing nutrient availability and killing Rhizobium, a nitrogen-fixing bacteria. 3 Agricultural lime ● Two forms of agricultural lime: ● calcitic lime: finely ground limestone, 80–90% CaCO3, < 14% MgCO3 ● dolomitic lime: finely ground limestone, 80% CaCO3, > 14% MgCO3. ● Application of lime: ● need for lime application is determined by pH ● soil characteristics determine quantity required ● apply three months before planting and before rainy season ● should be ploughed in deeply. ● Benefits of lime: ● physical eﬀect → improves soil structure ● chemical eﬀect → raises pH thus nutrient availability ● biological eﬀect → increases activity of soil microbes due to pH change. 4 The use of gypsum Gypsum is calcium sulphate (CaSO4) bonded to two molecules of water. ● Has many agricultural uses based on the fact that gypsum provides calcium ions: ● improves soil structure ● → provides calcium which flocculates clays in soil ● → decreases swelling and cracking in certain clayey soils ● helps prevent soil erosion 96 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 5 ● → makes soils more water permeable ● prevents waterlogging of soil ● → improves soil infiltration rate and hydraulic conductivity ● corrects subsoil acidity ● → prevents surface crusting and decreases the eﬀects of toxic soluble aluminium ● → of particular value as it reaches the subsoil which lime does not ● helps reclaim sodic soils ● → supplies calcium which replaces sodium held on clay colloids, thus allowing sodium to be leached ● → also decreases pH to values conducive to growth of most crops ● makes use of low quality irrigation water possible ● → reclaimed water is useable if gypsum and water-soluble polymers are added ● → sodium build-up in lower horizons is possible ● decreases heavy-metal toxicity ● → calcium prevents excess uptake of many heavy metals and prevents adverse eﬀects if they reach high levels ● decreases toxic eﬀect of sodium chloride salinity ● → calcium inhibits sodium uptake ● helps to keep clay oﬀ tuber and root crops ● decreases loss of fertiliser nitrogen to air ● → calcium decreases loss of nitrogen from ammonium by volatilisation ● → calcium also improves nitrogen uptake in young plants ● improves crop quality ● → calcium ensures good fruit quality. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 97

Unit 6 XX Organic fertilisers and fertilisation practices 1 Main types of organic fertilisers ● Plant-based organic fertilisers = kelp meal fertiliser, cottonseed meal, alfalfa meal, peat moss. ● Animal by-products = blood meal, bone meal, fish emulsion. ● Manure = farm manure, green manure (decomposing crop residue). Compost → oﬀers steady and slow release of all of the nutrients required by plants Table 15 Impact of organic fertilisers on the environment Positive effects Negative effects • provides minerals and improves structure; • release nutrients into their surroundings • helps soil to hold water; (streams, rivers, estuaries); • helps extra water to drain from soil; • overuse can dry out plants • cools soil in summer and warms it in winter; • stops soil from becoming hard, compacted; • binds soil 2 The concept: Green manure ● Green manure = type of cover crop grown to add nutrients and organic matter to the soil, e.g. ● legumes (used for their ability to fix nitrogen using bacteria). ● Characteristics of green manure crops: ● easily obtained seed, grow rapidly, deep root system, strong feeder, high fibre content. ● Cover crop is still in an immature succulent stage. Can be achieved in two ways: ● addition of green cuttings such as lawn clippings (small scale) ● addition of natural weeds or especially sown crops (large scale). ● Application of green manure: ● planted in the rainy seasons ● should be ploughed in at a mature stage but before they seed ● main crop should be planted immediately after green crop has decomposed. ● Benefits of green manure: ● addition of organic matter improves soil structure (by forming soil aggregates) ● increases nitrogen content of soil ● through decomposition it releases nutrients held within the green manure ● decreases water and nutrient loss (leaching) from soil ● prevents soil erosion ● assists in weed control and reduction of insect pests and diseases. 98 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 6 3 Description of farm manure Farm manure = organic matter used as organic fertiliser in agriculture. ● Consists of dung or faeces and urine of domestic animals, material used for bedding (straw, peat, muck, leaves, sawdust, shavings) and vegetable refuse. ● Animal manure = excreta (dung or faeces) of domestic farm animals: ● rich in nitrogen, smaller amounts of all other minerals ● slowly available to plants and not leached easily ● valuable by-product of livestock farming ● better to use dry manure to prevent scorching leaves. ● Liquid manure = useful way to give minerals to plants while they are growing: ● → immediately available to plants, but lost by leaching. ● To prepare → fill cloth sack with animal manure and hang in a drum of water for 1 week. ● Care needs to be taken not to get the liquid manure on the leaves or stems as it can burn them. Factors affecting composition of farm manure ● type and age of animal from which manure obtained ● type of ration fed to animals ● type and amount of bedding incorporated ● storage and handling of manure. 4 Description of compost Compost = organic matter that has been decomposed and recycled as a fertiliser and soil amendment. ● Contains all 14 minerals, but contains less nitrogen than manure. ● Preparation and requirements for compost production: ● large amounts of organic material from remains of crops, clearing of weeds, pruned branches and leaves, by-products of food processing ● source of nitrogen should be added ● agricultural lime should be added ● composting material must be packed in layers ● heap must be kept moist, but not too wet. ● Beneficial eﬀects of compost: ● physical eﬀects ● → maintains and increases the organic content of soil ● chemical eﬀects ● → contains almost all plant nutrients, but some may be in insuﬃcient quantities ● biological eﬀects ● → soil bacteria are added to soil. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 99

Unit 6 ● Organic products used as nutrient supplements: ● spent mushroom compost, bone-meal, hoof and horn meal, dried blood meal, fishmeal, seaweed extract, ash. 5 Fertilisation practices 5.1 Soil applications With soil applications, it is important to consider the water solubility of the fertiliser. ● Band placing: ● fertiliser can be placed in a ‘band’ close enough to supply young plants with nutrients eﬃciently, but not cause salt burns to roots ● common method of applying nitrogen and potassium fertilisers. ● Broadcasting: ● uniform distribution of fertiliser over planting area (top-dressing) ● usually worked or ploughed into the ground (base-dressing) ● used for crops that cover the land. ● Fertilisers that dissolve slowly require deep incorporation. 5.2 Foliar application ● Application of soluble fertiliser as fine spray or mist onto leaves with maximal coverage: ● add dispersants and apply during active growth periods of crops ● nutrients are readily available to plants ● suitable for most soluble fertilisers. 5.3 Fertiliser application through irrigation ● Applied by means of irrigation water or specially designed implements: ● irrigation systems can be used → microjet or drip irrigation are best ● sprinkler irrigation can be used but → take care not to burn foliage. 5.4 Aerial application of fertiliser ● Also known as aerial topdressing: ● involves aircraft that apply granular fertilisers (aircraft hire is costly) ● fast and economical, and suitable for areas that may not be accessible ● not suitable during windy periods. 5.5 Top-dressing and plant mixtures ● Can accompany band placing. ● Method replaces leached nitrogen while crop is growing: ● → put nitrogen fertiliser onto wet soil around plants ● = economical and eﬀective. 100 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 XX Plant reproduction: Sexual reproduction 1 Sexual reproduction in plants Sexual reproduction in plants = the reproduction of flowering plants by producing seeds → seeds formed after pollen from male part fertilises egg from female part of flower. 1.1 Functions and structures of the main parts of a flower petal stigma style pistil anther ovary stamen ovule filament sepal Figure 2 The main parts of a flower ● Female reproductive organ: ● → called the pistil – ● stigma is hairy and/or sticky to trap polled ● ovary produces eggs or ovules. ● Male reproductive organ: ● → called the stamen ● anther produces pollen. ● Non-sexual parts: ● → petals (collectively referred to as the corolla) and sepals (collectively referred to as the calyx) ● they support the sexual parts ● calyx protects the ovary ● corolla attracts insects to the flower. 1.2 Pollination ● Pollination = process by which pollen is transferred in plants, enabling fertilisation and sexual reproduction: ● pollen carried from anther to stigma ● pollen grain grows downwards towards the ovary and fertilises an ovule ● ovary forms the fruit, fertilised ovules develop into seeds. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 101

Unit 7 Self- and cross-pollination ● Self-pollination: when pollen that reaches the stigma comes from the same plant; occurs in plants where petals cover the stigma. ● Cross-pollination: when pollen comes from a diﬀerent plant of the same species; sometimes take place between species in the same genus. Cross-pollination is necessary to set fruit in two types of plants: ● protandrous plants: male and females parts in same flower, but pollen shed before stigma ready to receive it ● protogynous plants: pollen shed when stigma is old and can no longer receive it. ● Main agents of pollination: ● insects: e.g. fruit and vegetable plants ● flowers attract insects by producing nectar, strong smell and bright petals ● some plants have specific pollinators. ● small animals: e.g. birds, bats and mice (minor role in cross-pollination) ● birds feed on nectar, flowers have strong smell and bright petals ● wind: e.g. cereal plants ● no nectar, strong scent or bright petals ● male and female organs hang out of flowers. 1.3 The structure of a matured pollen grain and a receptive stigma 1.3.1 Matured pollen grain haploid generative tube nucleus nucleus nucleus mitosis exine intine young pollen mature pollen grain grain Figure 3 Structure of a mature pollen grain ● contains a tube nucleus and a generative nucleus ● generative nucleus divides to produce two sperm. 102 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 1.3.2 Receptive stigma stigma style ovary nucellus 3 antipodals ovary sac 2 polar nuclei (n) egg cell female ovule (n) gametes 2 synergids integuments micropyle Figure 4 Structure of a receptive stigma ● micropyle: opening in the ovule walls for pollen to enter ● nucellus: provides nutrition of ovule growth. 1.4 The germination of a ripe pollen grain on a receptive stigma until fertilisation pollen generative nucleus pollen tube tube ovule nucleus embryo Mitotic division sac of generative nucleus to form micropyle 2 male gametes Figure 5 Germination of ripe pollen grain on receptive stigma until fertilisation ● Pollen grain lands on stigma and germinates, forming a pollen tube. ● Tube nucleus controls its growth. ● Generative nucleus travels down tube and undergoes mitosis. ● Tube moves through micropyle into the ovule to begin fertilisation. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 103

Unit 7 2 Fertilisation process in plants 2.1 Fertilisation and double fertilisation ● Fertilisation = union of haploid male and female gametes to form a zygote: ● pollen tube enters ovule via micropyle ● → two male gamete nuclei are released into embryo sac ● one fuses with egg nucleus → diploid zygote (2n) ● one fuses with two polar nuclei → triploid endosperm nucleus (3n) ● tube nucleus disintegrates. ● Endosperm = nutrient-rich tissue that nourishes developing embryo. ● Referred to as double fertilisation because two sperm fuse with female gametes. 2.2.1 Development of a fertilised ovule to form a seed or fruit ● After fertilisation, zygote divides and diﬀerentiates into seed embryo: ● as embryo matures, integuments (outer layers of ovule) harden into seed coat ● ovule ripens to become a seed ● ovary ripens around the seed to form the fruit. 2.2.2 The concept: parthenorcarpy Parthenocarpy = fruit production without fertilisation of ovules, resulting in seedless fruit: ● Stimulative parthenocarpy: requires stimulation such as pollination. ● Vegetative parthenocarpy: no stimulation required: ● occurs naturally, e.g. ● wild parsnip ● can be induced artificially if desired, e.g. ● seedless grapes. 2.2.3 The concept: ablactation Natural tendency of fruit trees to shed some of their immature fruits is called ablactation. Happens when: ● Crop is too large = strain the tree’s resources and result in smaller fruits ● → tree sheds fruit. ● Climatic conditions, like excessive heat ● → tree will shed fruit (all of which use up moisture) to lessen the number of fruit that must use up resources. ● Also due to: ● soil factors, like the availability of moisture and nutrients. ● biological factors, like the presence of insects. ● management factors, like the spraying of trees with chemicals. 104 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 3 Seeds and fruit setting 3.1 The concepts: fruit setting and seed germination 3.1.1 Fruit setting ● Fruit = plant structure that contains its seeds = mature or ripened ovary of a flower: ● → setting occurs once flower petals fall and ovary has been stimulated to grow into a fruit. ● Mature fruit consists of: ● exocarp (skin), mesocarp (fleshy tissue), endocarp (forms boundary around seeds) ● → influenced by water shortage, pests, diseases, nutrient deficiency, heat and wind. 3.1.2 Seed germination ● Seed = small embryonic plant enclosed in covering or seed coat: ● → occurs with fertilisation and depends fruit set. 3.2 Development of seeds or fruits from a fertilised flower ● Ovules develop into seeds → ovary ripens to form a fruit: ● maturing seeds release a hormone ● → stimulates ovary wall to develop into a fruit ● other parts of the flower (petals, sepals and stamens) may fuse and ripen with the ovary to form the fruit – ● upper part of seed → becomes main area of growth ● lower part of seed → produces stalk which absorbs and manufactures nutrients. testa plumule cotyledons fruit radicle plumule seed coats epicotyl embryo seed micropyle hypocotyl endosperm radicle cotyledon cotyledon stalk The fruit Figure 6 Seed structure within a fruit (a) the fruit showing the seed inside; (b) a longitudinal section of the seed; (c) diagram of a seed structure © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 105

Unit 7 3.3 Types of fruits according to their development ● Simple and compound fruits: ● develop from single ripened ovary from a single flower ● ovary may be simple (one pistil or carpel), e.g. ● legume, nut ● OR ovary may be compound (two or more fused carpels), e.g. ● beans, mustard family. ● Aggregate fruits: ● develop from separate ovaries fused together in a single flower ● → called syncarps, e.g. ● strawberries, blackberries. ● Multiple fruits: ● ovaries develop separately into fruitlets ● → cluster together and develop into single fruit with central core when mature, e.g. ● pineapple, mealie. ● Accessory fruits: ● fleshy fruits that contain other plant tissues in addition to the ovary, e.g. ● entirely fleshy fruit (banana), the pome (apple), the pepo (cucumber), hesperidium (orange), drupe (peach), most aggregate and multiple fruits. 4 Seed germination 4.1 The process of seed germination ● Process 1: Imbibition ● phase I: seed absorbs water ● phase II: little absorption, increased enzyme activation and synthesis ● phase III: further water uptake, seed coat ruptures, radical emerges. ● Process 2: Respiration – when seed absorbs water, it also respires (anaerobic but later aerobic). ● Process 3: Activation of enzyme systems – food reserves are activated. ● Process 4: Radicle emergence and seedling growth – radicles move downward and form the root, shoot (plumule) emerges and grows upward. 4.2 The concepts: seed dormancy and scarification 4.2.1 Seed dormancy Seed dormancy = period of metabolic inactivity that precedes germination: ● germination will not occur even under favourable conditions ● dormancy period is broken by ‘after-ripening’ ● gives seeds better chance of survival. 106 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 7 4.2.2 Scarification Scarification = methods used to bring seeds out of dormancy: ● → breaching of natural seed coat by mechanical, thermal or microbial methods ● → mimics natural processes that weaken the seed coat before germination. 4.3 The basic requirements for seed germination ● Water: seeds need water to germinate, soak overnight in water to improve germination. ● Air: air in soil required for germination. ● Suitable temperature: most seeds germinate best at approximately 25 ºC: ● Cool-requiring seeds: ≤25 ºC, e.g. lettuce ● some seeds need period of cold before germination, e.g. apple. ● Warm-requiring seeds: ≥15 ºC, e.g. tomato. ● Cool and warm tolerant seeds: 5 ºC–30 ºC, e.g. carrot. ● Light: fresh seeds (not stored) require light, e.g. lettuce, many flowering plants ● → put thin covering layer of soil over seeds. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 107

Unit 8 XX Plant reproduction: Asexual reproduction Asexual reproduction in plants is the reproduction from pieces of the parent plant other than the seeds. 1 Types of asexual methods of reproduction 1.1 Separation and division of stems and roots ● Plants can produce stems or roots that store food. ● After growing season, shoots die down → remain dormant in soil until next season. There are four main types of specialised stems and roots: ● Bulbs: ● = grown mainly for their flowers (except onions) ● small, underground stems covered in fleshy leaves that store food ● new green leaves and flower stalk emerge from bulb in growing season ● buds grow on stems between leaves, e.g. ● onion family (grown from seeds), lily, tulip. ● To propagate: ● → dig up, separate and plant bulbs immediately that have died down after growing season. ● Tubers: ● = swollen ends of undergrounds stems ● buds on tubers grow into new plants, which produce new tubers, e.g. ● potato, yams and Jerusalem artichoke. ● To propagate: ● → planting whole tubers (preferable) or pieces of tubers (with at least one bud). ● Rhizomes: ● = underground stems with buds at joins of scale-like leaves ● new plants grow from buds to form clump of plants, e.g. ● banana, strelitzia, many grasses. ● To propagate: ● → separate new plants oﬀ clump (each needs piece of rhizome stem and some roots) or divide rhizome (each piece must have two or more buds). ● Stolons (or runners): ● = stems that grow at soil surface or just below ground (usually) ● form adventitious roots at nodes, and new plants arise from buds at plant base ● after formation of new plant, stolon usually dies away, e.g. ● strawberry, many grasses. ● To propagate: ● → dig up new plants, cut them oﬀ the runner and transplant. 108 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 8 1.2 Cuttings ● Cuttings are pieces of stems, leaves or roots from which new plants grow: ● stem cuttings develop roots ● root cuttings develop shoots ● leaf cuttings develop both shoots and roots. 1.2.1 Stem cuttings cut the top cut off the top end at an angle piece of the stem remove the bottom two leaves a piece of stem with four buds Figure 7 Taking a stem cutting ● Choose a healthy, productive plant. ● Do not plant upside down (i.e. angled end must be at the top). ● Dip bottom end into rooting hormone powder or liquid to improve rooting: ● roots grow from the part in the soil, new stems grow from buds above the soil. ● Keep soil moist and keep in the shade until growing well. 1.2.2 Leaf cuttings ● Can consist of leaf alone, leaf attached to leaf stalk, or leaf attached to small piece of stem by leaf stalk (latter is actually a stem cutting): ● shoot growth comes from bud between leaf and stem. 1.2.3 Root cuttings ● Usually taken in winter when plants not growing actively, e.g. ● guava, apple, oriental poppy, white poplar, rose, blackberry. ● To propagate: ● → plant cuttings horizontally in well-drained soil. 2 Oculation and grafting ● Oculation or budding = joining stem of one plant with buds from another so that they grow together as one plant. ● Grafting = joining stems of two diﬀerent plants so that they grow together as one plant. ● → Can only bud or graft together plants of the same genus. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 109

Unit 8 ● Scion = part of new plant that grows into the stem and branches. ● Rootstock = part of new plant that grows into the roots: ● can be either cultivar (grown from cuttings or layering) or seedling rootstocks ● cultivar preferred as characteristics are same as parent plant (i.e. known). ● Cambium = thin layer between bark and wood of stem: ● it is the reason for success of oculation and grafting ● can continue to grow after stem has been cut oﬀ ● two cambium layers must be placed next to each other. 2.1 Successful oculation and types of oculation ● Only bud onto young plants or smaller branches of large plants. ● Can topwork young trees by grafting buds onto small branches of upper part of trees. ● Grafting buds can ensure stronger join and less wind damage: ● = good method for small amount of scion wood. ● Time of the year is important: ● bark must separate easily from wood of rootstock ● buds must be dormant ● rootstock must be growing actively. ● → Late summer is best time. 2.1.1 T-budding ● Place bud 20 to 40 cm above soil. ● Bark must be smooth and protected from sun and wind. Figure 8 T-budding 2.1.2 Inverted T-budding ● Same as T-budding except T is inverted. ● Used to prevent rainwater or excess sap from running behind or into join. Figure 9 Inverted T-budding 110 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 8 2.1.3 Patch budding ● More diﬃcult than T-budding. ● Used on plants with thick bark. ● Bark of bud wood and rootstock must easily separate from wood. Preparing the bud Make two vertical cuts on each side of the bud. Use a double-bladed Remove the bud patch by knife to make two sliding it off to one side. horizontal cuts above and below the bud. Preparing the rootstock Use a double-bladed knife to make two Connect the two horizontal cuts about horizontal cuts with one third of the the vertical cuts. distance around the rootstock. Inserting the bud into the rootstock Insert the bud Wrap the union so that it fits with tape or waxed tightly on all cloth. Cover all the When the bud four sides. cuts but do not patch is ready, Trim the patch cover the bud. remove the on one side to bark from the make it fit rootstock. tightly. Figure 10 Patch budding 2.1.4 Chip budding ● Use if bark of rootstock does not separate from its wood. ● No protective flaps. Preparing the bud Preparing the rootstock Make a second cut about 1 cm above the About 2 cm above Make a cut Make a cut bud, coming the first cut, make about 1 cm about one a cut going downward behind quarter way below the the bud and downwards and bud. through the inwards until it connecting with the rootstock. first cut. Remove the reaches the bud piece. first cut. Inserting the bud into the rootstock Wrap with Insert the tape or bud into the waxed cloth rootstock to cover all chip. cuts. Do not cover the bud. Figure 11 Chip budding © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 111

Unit 8 2.2 Types of grafting Grafting = technique whereby vascular tissues from two plants are joined together: ● vascular joining is called inosculation. 2.2.1 Whip or tongue grafting ● Used to graft thin stems. ● Do in winter when plants are not growing. Preparing the scion Make a long, Make a sloping cut 2 second cut to 5 cm long one third of at the base of the distance the scion. from the tip of the first cut. Preparing the rootstock Make a long, sloping cut at Make a second the top of the rootstock, downward cut just cut the same length as the as for the scion. cut on the scion. Inserting scion into the rootstock Slip the rootstock and scion Lie and together so wax the that the graft. tongues lock. Figure 12 Whip or tongue budding 2.2.2 Cleft grafting ● Used for mango and avocado trees. ● Do in winter. Preparing the scion Preparing the rootstock Inserting the scion into the rootstock Tie and wax the graft Cut the scion Cut off the top of the Push the scion 20cm long. roostock 20 to 40 cm firmly into the Make two above the soil. Make cut on the sloping cuts one straight cut, the rootstock. 2 to 5 cm long. same length as the cuts on the scion. Figure 13 Cleft grafting 112 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 8 2.2.3 Wedge grafting ● Use for topworking trees. Preparing the scion Preparing the rootstock side view front view Cut the base of the scion to a long wedge, Use a thin-bladed saw to Widen the cuts sloping both downward and inward. make three cuts almost with a round-bladed to the centre of the stub. knife to fit the cuts on the scion. Put three scions into Cover the graft If the scions match the the stub. Match the union and the ends cuts in the stub, they are cambium layers of of the scion with held by tapping in place. the scion and rootstock. grafting wax Figure 14 Wedge grafting 2.2.4 Approach grafting ● Use for trees that are diﬃcult to graft, e.g. ● mango and macadamia. ● Best time is during active plant growth. With approach grafting, graft a plant in a container onto an established plant. Make the same cut on both stems. hold the two stems together and tie them with tape. Figure 15 Approach grafting © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 113

Unit 8 3 Advantages and disadvantages of asexual plant propagation methods 3.1 Advantages ● Fast growth. ● Same as parent plant so all plant characteristics known and good characteristics retained. ● Bear fruit in the first year. ● Can be used to grow plants that do not produce seeds, e.g. ● pineapples and bananas. 3.2 Disadvantages ● Plants may not grow in the same way as seed-propagated plants e.g. ● indigenous trees have deep taproot to reach groundwater during dry periods, but trees grown vegetatively develop fibrous root system which does not help survive droughts. 114 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 9 XX Plant improvement and biotechnology 1 Plant improvement 1.1 Selection Selection = process of improving cultivars by collecting seeds from the best plants: ● adapted to climate of the area ● resistant to pests and diseases found in those areas. 1.2 Hybridisation (hybrid seeds) Hybridisation = form of crossbreeding or controlled cross-pollination in plants. ● Take pollen from flowers of one cultivar and place on stigmas of flowers of second cultivar (anthers of second cultivar have been removed to prevent self-pollination): ● → hybrid plants usually better than both the parent cultivars. ● Use seeds of hybrid to plant next crop. ● May be used to produce disease-resistant plants. 1.3 Gene mutation Gene mutation = exposure of seeds to chemicals or radiation to change seed DNA and generate mutants with desirable traits, thereby improving plant production. ● Sometimes called mutagenic plants or mutagenic seeds. ● Methods: exposure to gamma rays, protons, neutrons, alpha and beta particles. ● Wheat, barley, rice, potatoes, soybeans, onions = bred genetically. ● Genetic breeding has produced plants with these properties: ● higher-yielding ● resistant to pests, diseases and drought ● adapted to environments and growing conditions of a region ● improved qualities, e.g. ● larger seeds, new colours, and sweeter fruits. 2 Biotechnology Plant improvement methods are often imprecise or yield results slowly. Therefore → use biotechnology. ● Biotechnology = any technique that uses living organisms (or substances from these organisms) to make or modify a product for a practical purpose. ● Agricultural biotechnology = understanding and manipulating genetic make-up of organisms for use in production or processing of agricultural products: ● → research into genome structure and genetic mechanisms that determine important traits is very promising. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 115

Unit 9 2.1 Genetically modified plants and their characteristics ● Created by genetic engineering, i.e. movement of genetic material between organisms to change characteristics. ● Also called transgenic organisms. ● New characteristics include: ● plants that are resistant to diseases, pests and stress ● fruits and vegetables that stay fresh for longer ● plants that possess healthy fats and oils and increased nutritive value ● soybeans with a higher expression of naturally occurring anti-cancer proteins ● higher value-added feed for livestock ● higher fibre extraction rates in paper and pulp industry (lignin modification in trees) ● biodegradable plastics, prophylactic and therapeutic vaccines. 2.1.1 GM crops in South Africa ● Examples = maize and cotton (insect resistant and herbicide tolerant), soybean (herbicide tolerant). ● GM crops: 51% yellow maize, 62% white maize, 80% soybean and 90% cotton. ● Most popular: Bt insect resistant maize ● Bacillus thuringiensis (Bt) is a bacterium toxic to certain insects ● GM plant known as Bt cotton or Bt maize. ● Second most widely used: Roundup Ready (RR) herbicide-tolerant maize ● stalk borer resistance built into the seeds ● less sensitive to harmful eﬀects of herbicides. ● Stacked traits Bt+RR sales commenced in 2007. ● Field trials of drought-resistant maize varieties underway. 2.2 Advantages and disadvantages of genetic modified crops or plants 2.2.1 Advantages ● Environmental: ● → fewer harmful chemicals washed into soil (farmers can use less pesticide on insect resistant plants). ● Health: ● → produce healthier food (farmers use less pesticide on insect resistant plants). ● Economic: ● → lower production costs (less susceptible to viruses and insects, hardier crops, reduced need for pesticides and/or herbicides). ● Yields: ● → more consistent yields (less susceptible to disease, insects and herbicides); higher yields (improved seeds). 116 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 9 2.2.2 Disadvantages ● Environmental: ● → indiscriminate use of weed killers on herbicide resistant crops (as they are less susceptible to these chemicals). ● Health: ● → long-term eﬀects have not been established. ● Economic: ● → too costly for small-scale farmers (GM seeds include a ‘technology fee’) ● → some traits do not benefit small-scale or subsistence farmers (e.g. herbicide resistance – if they cannot aﬀord herbicides) ● → seeds cannot be retained for breeding (due to patent). © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 117

Unit 10 XX Weed management control 1 Weeds and herbicides ● Weeds: ● = plants not planted by farmer that compete with planted crop for space, sunlight, nutrients ● → can be herbs, ground covers or creepers; annuals or perennials. ● Herbicides: ● = chemicals that kill or interfere with growth of specific weed targets – ● → act by altering metabolic processes but leave planted crop relatively unharmed ● decompose rapidly in soil via microbial decomposition and hydrolysis. ● Common weeds: ● Common blackjack (Bidens pilosa): ● → seeds stick in clothing and animal hair and germinate in dense mats ● → spreads fungus disease to potatoes, tomatoes, and cotton; easily controlled with post-emergence herbicides. ● Common thorn apple (Datura stramonium): ● = tall, aggressive growing, poisonous annual ● → poisonous seeds found in thorny pods, contaminate maize grain. ● Morning glory (Ipomoea species): ● = aggressive fast-growing creepers that smother or strangle crops ● → trumpet-like flowers of various colours ● → seeds germinate and grow rapidly, contaminate grain crops. ● Creeping sorrel (Oxalis species): ● = small plant with underground bulb or stolon ● → diﬃcult to remove as parts remain in the soil and regrow ● contains oxalic acid which poisons livestock. ● Parasitic weeds = feed directly oﬀ other plants: ● → e.g. dodder (Cuscuta campestris): ● = yellow thread-like stems and seeds, lacks chlorophyll so cannot produce own food ● → seeds germinate or it regenerates from pieces of stem ● → reduces production or kills host plant (e.g. lucerne) ● → must be physically removed and burned since herbicides ineﬀective. ● → e.g. witchweed (Striga asiatica) ● = indigenous semi-parasite of grass, maize and tobacco roots ● → seeds (500 000 per plant) germinate near plants that secrete strigol ● → well fertilised host plants can survive, beans can cause ‘suicide germination’. 118 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 10 2 The impact of weeds on agriculture ● Can grow on poor, exposed soil that other plants cannot. ● → Sometimes referred to as pioneers: ● prevent soil erosion and improve soil condition for later growth of other plants ● compete with planted crops for resources and may aﬀect their growth and health ● seeds germinate more quickly and young plants grow rapidly ● source of plants pests which spread to crop seedlings ● encourage insects which damage crops ● contaminate final product and interfere with crop harvesting. ● Alien or exotic weeds: ● do not have natural predators in South Africa and can become invaders, e.g. ● Lantana (South American bush spread by birds) ● black wattles ● Sesbania (grows along watercourses and drains natural springs) ● bankrupt bush or Seriphium plumosum (dominate livestock grazing or pasture, make it unpalatable). 3 Features of weeds that make them successful 3.1 Adaptive features of weeds ● Hairs on stem or leaves → protects from herbivores, reduces water loss. ● Waxy or small leaves → reduces water loss. ● Multiple flowers or fruit → many seeds mean higher reproduction rate. ● Strong root system → grow in high erosion areas and nutritionally poor soil, maximise water uptake, roots not loosened easily. ● Root nodules containing nitrogen-fixing bacteria → allow growth in low nitrogen soils. ● Rhizomes → deep roots ensure spread easily and quickly, removal diﬃcult. 3.2 Properties that allow weeds to grow more easily than crop plants ● Produce large seed quantities → germinate rapidly. ● Rapid growth → deprived crop seedlings of sunlight. ● Aggressive growth → choke plants or smothering crop seedlings. ● Spread eﬃciently → by wind, birds or animals. ● Resist harsh weather conditions (such as drought or cold). ● Produce growth-inhibiting substances (e.g. bankrupt bush). © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 119

Unit 10 4 Agents of weed dispersion or transmission ● Animals: ● seeds pass through digestive tract (birds and mammalian herbivores) and are deposited in faeces ● ants carry seeds to nests, discarded with other refuse ● seeds or seedpods cling to animal fur and human clothing and then drop oﬀ. ● Machines: ● seeds present in soil are exposed to light and air by ploughs during cultivation ● farm vehicles transfer seeds stuck in their tyre treads. ● Wind and water: ● wind spreads seeds that are tiny, have tufts of hair, and are ‘winged’ ● plants break oﬀ at stem base and scatter seeds like a tumbleweed ● seeds of wetland species float and are carried downstream (or blown by wind). ● Mechanical ejection: ● release mechanism of mature seedpods, i.e. seedpods burst open and propel seeds away from plant, e.g. ● Oxalis stricta. ● Other dispersion methods: ● crop seeds or compost contaminated with weed seed. 5 Methods of weed control 5.1 Mechanical weed control ● Hand weeding: ● → used when rows of plants are close together. ● Cultivation: ● → remove weeds by hand using tools (e.g. hoes) within a month of appearance ● do on hot dry days when weeds will die. ● Mulching: ● → mulch between vegetable or crops rows will suppress and smother weeds. ● Solarising: ● → black plastic laid on ground will absorb heat and kill underlying weeds. 5.2 Chemical (herbicide) weed control 5.2.1 Selectivity ● Herbicide selectivity = susceptibility or tolerance of diﬀerent plants to herbicide: ● → non-selective: kill most plants and could also kill the planted crop ● → selective: at correct dose they kill weed but not crop. 120 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 10 5.2.2 Method of action ● = way in which herbicide acts on weeds: ● → contact: only aﬀects parts of plant onto which applied (usually the leaves) ● → systemic: absorbed through roots and spread into whole weed by translocation. 5.2.3 Time of application ● = stage of weed development at which applied: ● → pre-emergence: applied before weeds emerge, absorbed by developing root or shoot ● → post-emergence: applied after weeds have emerged. 5.2.4 Application of herbicides ● Use correct herbicide and strictly according to instructions. ● Excessive use can lead to herbicide resistance. ● Available in various formulations: ● powder, granules or liquid concentrate (diluted in water and spray) ● granules for scattering in soil ● gel for applying on stems or stumps ● oils for diluting in diesel. ● Example = phosphorous herbicide group: ● used post-emergence, non-selective, act systemically, inhibit amino acid formation ● e.g. triazines and ureas, acetanelides, phenoxy compounds. 5.3 Biological weed control ● Uses natural organisms to control weeds → insect predators or fungal diseases. ● example in South Africa: ● cochineal bug (Dactylopius ceylonicus) eradicated prickly pear cacti (Opuntia ficus-indica) → bug was bred in laboratories and used to suck sap from leaves → spread by birds that visited prickly pears for fruit. ● Pest must be highly specific to prevent spread to other plants. ● Advantages: ● → environmentally friendly, self-sustaining, cost eﬀective. ● Disadvantages: ● → slow, unpredictable, relatively expensive. 5.4 Integrated weed control ● Integrated weed control = management approach to weed control focused on prevention rather than eradication. ● Advantages: ● → cost eﬀective, labour eﬀective, reduces reliance on chemical control. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 121

Unit 10 ● Principles of integrated weed control: ● cultural methods → good seedbed preparation to minimise weed problems ● optimal herbicide use → only when weeds susceptible, correct product for weed type, only if weather suitable, apply evenly ● crop rotation → rotate or alternate to provide competition for weeds ● total farm hygiene → managing weeds on farm as a whole. ● Other weed removal options: ● = animals to graze non-poisonous weeds, burning of weeds, smother crops (e.g. lucerne). 122 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 11 XX Plant diseases and pest control 1 Plant diseases and their control ● Diseases caused in plants by pathogenic micro-organisms, e.g. viruses, bacteria and fungi: ● → micro-organisms are adapted to invading plant tissues. 1.1 Type of plant diseases caused by micro-organisms 1.1.1 Viral diseases ● Symptoms: ● = spotting, mottling, twisting, distortion, wilting, or death of leaves; bark of trees are less commonly aﬀected. ● Methods of transmission: ● = seeds – ● → spread through pollen during fertilisation and then through seeds ● = vegetative – ● → subdivision by vegetative reproduction (bulbs, cuttings or runners) ● = mechanical – ● → by means of infected sap (by infected pruning or cutting tools) ● = pests – ● → sucking insects and nematodes transmit when piercing plant cells ● Mechanism: ● → inhibit growth and prevent production, e.g. ● mosaic virus (tobacco plants, tomatoes and maize), greening virus (citrus plants). 1.1.2 Bacterial diseases Plant bacteria found in soil, on living plants, or on plant debris. ● Symptoms: ● = rot, wilt, galls, spots, canker (similar to fungi). ● Transmission: ● → infected seeds, wind, contact with infected plants. ● Mechanism: ● → kills young plants, deforms leaves, rots leaves or stems, spoils fruit, e.g. ● bacterial wilt of potatoes (caused by Pseudomonas solanacearum) ● crown gall of tobacco (caused by Agrobacterium tumifasciens). 1.1.3 Fungal diseases ● Symptoms: ● = characteristic pattern and discolouration of leaves. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 123

Unit 11 ● Transmission: ● → fungi spores that are spread in soil or by wind or water. ● Favourable conditions: ● = moisture, low light intensity, high humidity (during overcrowding), e.g. ● damping oﬀ (horticultural crops) ● downy mildew (vines) ● powdery mildew (wheat, onions). 1.2 The control of plant diseases 1.2.1 Bacterial and viral plant diseases ● No treatment, so must prevent or control: ● measures include – ● → eradicate infected plants ● → use clean seed, plant stock, and tools ● → control plant pests ● → do not smoke when handling plants ● → ensure good soil condition and use disease-resistant cultivars ● → rotate crops, use intercropping, and sow with recommended spacing. 1.2.2 Fungal plant diseases ● Use same methods as for bacterial and viral diseases: ● fungicides: ● → available for some diseases, use correct product and apply correctly, some seeds are pre-treated with fungicides. ● watering early in the morning and avoid overcrowding of plants. 2 Pesticides, plant pests and their control ● Pesticides = substance used to prevent, destroy or repel pests. ● Pesticide formulations = chemical, biological, antimicrobial. ● Pests = invertebrate animals that feed on various plant parts, e.g. ● arthropods (insects, mites), worms, molluscs (snails, slugs). 2.1 Plant pests ● Insects: ● = six-legged arthropods or jointed-legged animals, e.g. ● various bugs (aphids, leaf hoppers and scale insects) ● grasshoppers ● caterpillars (larval forms of butterflies and moths) ● beetles ● flies, ants and termites. ● Some are beneficial because ● → they eat pests or help pollinate crops and fruit trees. 124 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 11 ● Mites: ● = arthropods with eight legs – ● → live in plant debris and feed on dead organic matter ● Some are parasites ● → damage crops. ● Molluscs: ● = soft un-segmented bodies, some have protective shell ● → most troublesome during wet seasons ● → eat live plant material. ● Nematodes: ● = tiny parasites found in soil and plant material ● → found in huge numbers (up to 40 000 in roots of one potato plant). 2.2 Type of damage caused by pests on plants ● Damage on visible parts of plant (leaves, fruit, flower buds, stems, barks or roots) or seeds: ● → prevents plant nutrition or reproduction. ● Sucking pests: ● suck sap from plants ● → aﬀected parts dry out, deform and become mottled ● found on undersides of leaves, e.g. ● leaf suckers (aphids, thrips) ● stem suckers (scale insects) ● fruit suckers (moths, scale insects, mites, thrips). ● Chewing and stinging pests: ● eat various parts of plants, causing damage or scarring, e.g. ● leaf damage (grasshoppers, caterpillars) ● flower damage on fruit trees (CMR beetles → prevents fruiting) ● fruit damage (fruit flies → lay eggs in developing fruit or vegetable) ● seedling damage (cutworms) ● stem or root damage (termites, woodborers) ● stored grain or seed damage (beetles, weevils, grain moth larvae). ● Eelworms: ● = tiny nematode worms occurring in very large numbers in soil ● → parasitic eelworms infest plant roots (e.g. tomatoes and potatoes) ● → only controlled by soil fumigation. 2.3 The control of plant pests 2.3.1 Chemicals (pesticides) ● Pesticides = registered chemicals for use against pests: ● also poisonous to animals and humans so use with care ● trained operators required when using large quantities. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 125

Unit 11 ● Precautions when using pesticides: ● use correct product, correct amount and at correct stage ● ensure correct interval between application and harvesting ● follow safety directions ● do not dispose of into water sources. ● Methods of applying pesticides: ● leaves → reapply, especially after rain ● fruit → apply at certain stages, e.g. ● to prevent fruit fly attacks ● vegetables → apply post-emergence ● stored grain and seeds → apply directly or into storage containers ● soil → apply in granular form or as a fumigant. 2.3.2 Biological methods of pest control ● Involve the use of natural organisms to control pests: ● predators → animals that eat plant pests, e.g. ● ladybird larvae eat aphids ● parasitoids → parasites that breed in the body of pests and then eat them from the inside, e.g. ● very small wasps ● transgenic plants → genetically modified, disease resistant plants, e.g. ● BT maize (poisons bollworm that feed on maize). 3 Integrated pest management (IPM) IPM is a pest management system that uses: ● good cultivation practices based on an ecological approach ● chemical and biological pest control methods. IPM is based on five main principles. 1 Monitoring and record-keeping: ● regular observation of crops, accurate pest identification, recording of pest behaviour and reproductive cycles. 2 Acceptable pest levels: ● establish acceptable pest levels called action thresholds. 3 Preventive cultural practices: ● select best varieties for local conditions, maintain healthy crops, quarantine plants, use of cultural techniques, e.g. ● removal of diseased plants. 4 Mechanical and biological controls: ● mechanical methods are first options, e.g. ● handpicking, using traps; biological control via conservation of natural predators or their introduction. 126 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 11 5 Responsible pesticide use: ● only used as required and at specific times in pest lifecycle. 3.1 Benefits of integrated pest management ● Reduced exposure to hazardous chemicals → human and environmental, thus reduced cost of pesticide application. ● Environmental improvements to farms → enhance long-term sustainability. ● May be only solution to long-term pest problems. 3.2 Steps to follow in implementing integrated pest management 1 Proper identification of pests: ● → ensures eﬀective action is taken. 2 Learn pest and host lifecycle and biology: ● → helps determine likely time of outbreak ● → can remove conditions needed to survive. 3 Monitor the environment for pest population: ● → ensures timely action is taken ● determine distribution and if population is increasing or decreasing. 4 Establish action threshold: ● → point at which cost of pest damage exceeds cost of pest control. 5 Choose an appropriate combination of management tactics: ● → mechanical, cultural, biological, and chemical controls. 6 Evaluate results: ● → Desired eﬀect? Satisfactory prevention or management? Satisfactory method? Unintended side eﬀects and their future prevention? Future plans? 4 Insect control in stored seed and grass 4.1 Conditions that influence insect damage to stored seeds or grains ● Length of storage: = six weeks requires protection from possible damage. ● Moisture content: store when dry (high moisture → increased temperature → reduce eﬃcacy of grain protectants → insects multiply) ● therefore: aerate containers to cool seed and grain. 4.2 Lifecycle of some pests or insects of stored agricultural products Take action when pests or insects reach the stage at which they can cause damage and/ or be most easily eradicated. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 127

Unit 11 Table 16 Common pests in South Africa that damage stored seed and grain Pests Crops / products Lifecycle Optimal Larvae development conditions Maize weevil maize crops ~5 weeks 27–31 oC in individual grain, (Sitophilus zeamais) (30 oC, 70% RH) > 60% RH eat from inside out, reproduce and release larvae Flat grain beetle grain, cereal 22–24 days 25 °C (Cryptolestis) products (32–35 °C, 75% 75% RH RH) Tropical warehouse rice, wheat, 45–55 days moth (Ephestia maize, beans, (28 ºC, 70% RH) cautella) cotton seeds, cereals Lesser grain borer cereals, seeds, 1–2 months 32 oC in loose grain, bore (Rhyzopertha dried fruit, almost (25 days if ideal 12% RH into damaged kernels, dominica) all grains conditions) adults chew their way out 4.3 Various methods of controlling insects in stored seeds or grain ● The goal for control methods = relatively insect-free, no insecticides or fumigants ● Methods: ● clean old grain, grain debris and ensure it is dry ● spray empty bins with insecticide ● aerate grain to cool it ● regular measurement of grain temperature and sampling for insects. ● → Pesticides can be used if required, e.g. ● Super Guard (dust formulation) ● K-Obiol (surface spray and fog) ● aluminium phosphide fumigants (toxic, restricted use). 5 Plant protection and the state ● Plant protection = control of plant pests in agriculture. ● Various organisations provide advice and information, and conduct research: ● Plant Protection Research Institute (PPRI) of the Agricultural Research Council ● The Directorate of Plant Health and Quality, National Department of Agriculture. ● Role of the state in plant protection: ● prevent importation of diseased plants and pests ● impose control measures for disease or pest threat. 128 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

X 3 Topic XX Unit Topic questions ● Answer the questions below. ● Give yourself one hour. ● Check your answers afterwards and do corrections. 1 Which chemical reaction best describes the process of respiration? (1) a CO2 + H2O + energy sun → carbohydrates + O2 b carbohydrates + O2 → CO2 + H2O + chemical energy 2 Describe the importance of photosynthesis. (4) 3 List three minor macro-elements found in soil. (3) 4 Pair up the statements in the two columns which describe the major macro-elements found in soil. (6) a major form of this element in i can be absorbed from soil is NO3– phospholipids b H2PO4– is the major form of this ii constituent of proteins and element in soil nucleic acid c toxic levels of this element iii regulates flow of soil water produce acidic and sour citrus fruit 5 Briefly describe leaf sample analysis as a method of determining the nutritional status of soil. (4) 6 Name two factors that aﬀect the availability of nitrogen in soil. (2) 7 Provide a word or term to match each of the following descriptions. a A chemical preparation consisting of inorganic salts that is applied to soil or plants. b A type of cover crop grown to add nutrients and organic matter to soil. c A type of fruit production that results in seedless fruit. d A management approach to weed control focused on prevention rather than eradication. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 129

X 13 Topic XX Unit Topic questions e The most successful genetically modified plant used in agriculture in South Africa. f The male reproductive part of plants that produces pollen. g A period of metabolic inactivity that precedes germination. h The hairy/sticky female part of a plant that traps pollen. 8 x 2 = (16) 8 A farmer applies the fertiliser 3:2:1(22) to the soil. Calculate the percentage of potassium in the mixture. Show your calculation. (3) 9 Provide the common name for CaCO3NH4NO3, a nitrogenous fertiliser. (1) 10 Which fertiliser contains the highest percentage of potassium: KCl or K2SO4? (1) 11 Name three beneficial eﬀects of compost. (3) 12 Describe broadcasting in the context of fertilisation practices. (3) 13 Briefly describe the process of pollination and how it leads to the formation of a fruit. (4) 14 Explain what is meant by asexual reproduction in plants. (1) 15 Name four main types of specialised roots and stems. (4) 16 State the parts of two plants that are joined in the process of : a oculation b grafting. (2) 17 Explain briefly how hybrid plants are bred. (2) 18 Name two common parasitic weeds. (2) 19 Briefly describe how birds and machines disperse weeds. (5) 130 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

X 3 Topic XX Unit Topic questions 20 Which statement is incorrect? a Pesticides i are used to prevent and repel pests. ii can be disposed of into water sources. iii can be formulated as antimicrobials. b Viral diseases i may be spread by pests. ii inhibit growth and prevent production of plants. iii do not usually aﬀect plant leaves. c IPM principles i include early and accurate identification of pests. ii include the use of pesticides before mechanical methods. iii require the establishment of action thresholds. 3 x 1 = (3) Total: 70 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 131

Topic 4 Unit X XX Optimal resource utilisation Overview UNIT 1 Page 133 • The concept: soil survey Soil surveying and • The soil survey process in agriculture planning • The concept: precision farming • Ultramodern technologies used in precision farming • The concepts: irrigation and irrigation schedule UNIT 2 Page 138 • Main sources of water for irrigation Water use and • Criteria to determine water quality for irrigation irrigation • Irrigation systems • Reasons for and advantages of irrigation scheduling • How to determine the moisture content of soils TOPIC 4 Page 132 Optimal resource utilisation UNIT 3 Page 145 • The term: soil drainage Soil drainage, • Primary and secondary soil cultivation: aims and cultivation and crop diﬀerences rotation • Diﬀerent types of soil cultivation systems • The concept: crop rotation UNIT 4 Page 150 • The concept: greenhouse Greenhouses, • The concept: hydroponic production systems hydroponics and • The concept: aquaculture aquaculture 132 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 XX Soil surveying and planning 1 The concept: soil survey ● Soils surveying: process of determining characteristics and quality of soil in an area so that authorities or farmers can develop an appropriate land-use plan ● Main characteristics to consider: ● soil texture ● soil depth ● rockiness of soil ● amount of soil erosion ● slope. Soil texture ● Fine and medium texture soils (clay, clay loam and sandy loams) retain water and nutrients better than sandy soils ● → thus have higher agricultural potential. ● Clay soils hold more moisture than sandy soils ● → thus respond more slowly to changes in air temperature during spring and autumn. Soil depth ● Defined as height of soil layer above the rock layer ● measured with soil auger. ● Most crops require soil depth of at least 90 cm with good drainage. ● some vegetable crops grow in shallow (50 cm), well-drained soil. Soil rockiness ● Refers to size and abundance of rocks or stones in an area – ● measured with rockiness index: ● → volume of rocks as % of total soil volume. ● High stone content or rockiness leads to poor water retention of the soil ● → aﬀects ease and cost of cultivation. Soil erosion ● Transport of soil by natural forces (mainly water and wind) ● → removes nutrient-rich lighter soil fractions and damages soil fertility. ● Types of soil erosion: ● rill erosion – rills are small furrows caused by surface runoﬀ on bare soil, often begins on paths used by people ● donga erosion – dongas or gullies form when smaller rills become deeper and wider ● sheet erosion – removal of thin top layer evenly over a large area, caused by strong winds or heavy rain in an area with little or no vegetation. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 133

Unit 1 XX ● Signs of soil erosion: ● dust storms ● streams, rivers and dams carrying muddy water ● dams that are silted up and filled with mud ● new soil deposits ● deep footpaths ● plants with uncovered roots ● pedestals ● bare ground with poor plant growth. Slope ● Aﬀects soil erodibility, thus used to determine land-use class numbers (1–7). ● Steepness indicated on contour maps by closeness of contour lines. ● Aspect of the slope: ● direction to which slope faces → aﬀects vegetation, wildlife and parasites that may occur there ● N-facing and W-facing usually hotter and dryer than S-facing and E-facing slopes, respectively. ● Waterways usually occur at the bottom of slopes: ● → soil in and around these diﬀer. 2 The soil survey process in agriculture The soil survey process in agriculture is made up of the following steps: ● Statement of objectives ● Background study: ● find out what area was used for; get information from aerial photographs, orthophoto maps (satellite photos made into maps), previous survey reports; gather on-site information (e.g. erosion and slope) ● Fieldwork: ● = detailed study of the area and main soil characteristics (texture, depth, rockiness, erosion – amount and likelihood of, slope) including their measurement ● Soil sample analysis: ● usually done in a soil laboratory ● Interpretation and implementation of information: ● determine land-use class (1–7) ● develop a soil map ● = shows distribution of soil types and/or soil properties in area of interest: ● used for land evaluation, spatial planning, agricultural extension, environmental protection and similar projects. 134 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 XX Developing a soil map ● Obtain outline map of area – ● 1:10 000 orthophoto map or traced outline of map is best. ● Make observations about land (e.g. signs of erosion and type) ● Auger the soil ● Find soil texture ● Find soil depth ● Use codes to indicate information on map ● S: soil type, D: soil depth, N/S etc., R: rockiness, E: erosion as follows: ● S1 . D3 ● N. R1 . E2 Table 1 Features of land in each land-use class Land-use Best use for that land-use Rockiness Soil type Soil depth Erosion Slope class number class 1 Annual cropping R1 S2–4 D1 E1 A 2 Cropping with cover crop R1 S2–4 D2 E2 B 3 Cover crop and trees with R1 S1–5 D3 E2 C some cropping 4 Permanent pasture R2 S1–5 D3 E3 D 5 Veld R3 S1–5 D4 E3 E 6 Forestry R3 S2–4 D4 E3 F 7 Wildlife R4 Sw D4 E4 F Xw Table 2 Explanation of codes in Table 4.1 Soil texture Soil depth Rockiness Erosion Slope S1 sandy D1 greater than R1 less than E1 no signs of erosion A D–3° 90 cm 10% rock S2 sandy loam D2 50–90 cm R2 10–20% E2 shallow rills and/or deep B 3–8° rock paths S3 loam D3 25–50 cm R3 20–50% E3 deep rills or sheet ero- C 8–15° rock sion S4 clay loam D4 less than R4 more than E4 dongas D 15–25° 25 cm 50% rock S5 clay E 25–35° Sw waterlogged F more than 35° Xw waterway © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 135

Unit 1 XX 3 The concept: precision farming ● Modern method of crop farming management, uses traditional soil survey and ultramodern techniques. ● Basic principles: ● → to manage small areas within fields (and not whole field as single unit) ● → farm with most productive crop ● = to get best return (profit or yield) per hectare of land. ● Basic aims: ● → minimise inputs ● → maximise yields ● → use sustainable practices (e.g. pest, water and nutrient management). ● Method: ● → collect detailed information on climate, geography, soil, specific crop needs, and weather ● information analysed by sophisticated computer software programs: ● Provides precise data on subfields on a farm: ● optimum sowing densities ● fertiliser estimates and other input needs ● irrigation needs ● accurate crop yield predictions. ● Advantages: ● optimal production ● less damage to the environment ● sustainability of production ● healthier food, and traceability of foods produced and consumed. 4 Ultramodern technologies used in precision farming Geographic Positioning Systems (GPS) ● Satellite network that orbits Earth and provides precise satellite and time location information to ground receivers: ● → obtain precise co-ordinates of any location in a field. Geographic Information Systems (GIS) ● Computer software database system: ● → used to input, store, retrieve, analyse and display information in map-like format ● = analyses inputs and ● determines water and fertilisation management system. 136 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 1 XX Remote Sensing Systems ● Use of aerial photography or satellite imagery to measure various aspects of soil or crop in specific places, combined with other information gained in GIS ● information obtained includes: ● vegetation indexing (measuring type and amount) ● soil drainage maps ● colour infrared aerial photographs (information on soil type and soil moisture) ● crop health monitoring (infrared photography used to detect or measure plant stress and crop evaporation or transpiration rates). Google Earth ● Website that provides satellite imagery ● + can be integrated with GIS ● → enhances planning of fields, crops and other structures (dams, roads and buildings). Yield monitors ● Crop yield measuring devices located in harvesting machinery: ● store crop yield at every specific sit, ● correlate with GPS co-ordinates and integrate in GIS. Variable Rate Fertilisation (VRT) ● Fertiliser field application equipment controlled by integrated information on GIS: ● → delivers exact amount of fertiliser needed at every identified site. ● Ensures: ● optimum production ● Reduces: ● wastage and environmental eﬀects of fertiliser. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 137

Unit 2 XX Water use and irrigation 1 The concepts: irrigation and irrigation schedule ● Irrigation used to supplement rainfall in drier parts of South Africa: ● → allows farmers to grow crops with high water requirement and during the dry season. ● Definitions: ● irrigation ● = moving or supply of water from water source to site of growing crops to improve its production ● irrigation schedule ● = plan developed by a farmer showing when and how much water to supply to a particular crop to ensure optimal production. 2 Main source of water for irrigation Groundwater ● This is rainwater that has seeped into soil and moved down to rock layer below. ● Natural sources: ● spring: occurs when layer of rock has thin soil layer thus water seeps or flows out onto the soil surface ● vlei: occurs in low-lying areas where groundwater may rise to the surface during high rainfall periods. ● Constructed sources: ● well: shallow holes dug to access groundwater above layer of rock, provides limited water supply ● borehole: narrow and deep hole which penetrates upper layers of rock, supplies significant amounts of water. Surface water ● Occurs when rainwater runs over soil surface instead of seeping into soil: ● forms streams → flow into rivers → flow into constructed dams, lakes or the sea. ● Dams store surplus water during rainy season. ● Irrigation water can be drawn directly from large rivers, lakes or dams. 3 Criteria to determine water quality for irrigation ● First determine if suﬃcient water is available. ● Then consider if water quality is suitable for irrigation: ● → rainwater is clean, pure and contains no salts; groundwater may contain salts and/or pollutants. 138 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 XX ● Sample water and analyse at a laboratory: ● salinity: total amount of dissolved salts ● sodicity: amount of sodium containing salts ● toxic chemicals: e.g. boron, manganese or iron ● turbidity: amount of suspended soil particles in water (can block irrigation systems, wear out pump impellers) ● pollutants: ● biological – faecal bacteria from sewerage (e.g. Escherichia coli) ● chemical – phosphates and nitrates (city waste water and runoﬀ from fertilised lands), and pesticides (in runoﬀ). 4 Irrigation systems ● Step 1: find suitable water source ● Step 2: move water to land to be irrigated ● Step 3: spread water evenly over area Irrigation systems Flood irrigation Overhead (sprinkler irrigation) Furrow Basin Permanent systems Moveable systems • Drip irrigation Quick-coupling Variations: • Centre pivot • Dragline • Gun stand and gun • Travelling irrigation Different irrigation systems 4.1 Flood irrigation ● Water is released into the ground and led down a slope to where it is needed ● water led via furrows or basins. Furrow irrigation ● Construct furrows for water to flow down (using hoe or plough, animal- or tractor drawn) ● crops planted on ridges of soil between furrows ● only use on gentle slopes (< 5% gradient) to avoid excessive erosion. ● Main canal/furrow is along contour at top of slope (made of soil, stone, brick or concrete) ● source water is fed into main canal ● openings at intervals along main canal allow water to run down the irrigation (or secondary) furrows, one at a time. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 139

Unit 2 ● When one furrow is flooded, soil is pushed back to close furrow and open canal above next furrow. ● Horizontal drainage stream at bottom of slope removes excess water and leads it into a tank (can be pumped back to main canal). Basin irrigation ● requires flat or gently sloping land (< 5% gradient) ● soil walls divide field into a number of basins ● starting from a main canal, water is led from basin to basin ● each basin must be flat ● e.g. around fruit trees, rice (grows well in shallow water). Table 3 Advantages of flood irrigation systems Furrow irrigation Basin irrigation No power needed (depends on position of water source) √ √ No expensive equipment needed √ √ Easy to set up and manage √ √ Even spread of water √ √ Table 4 Disadvantages of flood irrigation systems Furrow irrigation Basin irrigation Requires a lot of water √ √ Difficult to control delivery of water √ √ Difficult to set up and manage √ √ Uneven spread of water √ √ Erosion may occur (gradient >5%) √ √ 4.2 Sprinkler or overhead irrigation ● Delivers water like rain onto the crop. ● Two main types: permanent systems and moveable systems. 4.2.1 Permanent systems ● has permanent laterals and sprinklers ● uses valves to irrigate diﬀerent blocks at a time ● disadvantages: expensive and inflexible in their use ● advantages: low labour requirements, less sensitivity to wind, no soil or crop damage occurs due to movement of pipes. Drip irrigation/micro-irrigation ● relatively permanent system (pipes remain in situ for growing season or longer) ● plastic mother line/mainline runs from water source along one edge of field to be irrigated ● narrow plastic pipes branch oﬀ at intervals and run along length of each plant row 140 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 XX ● type of crop determines spacing between branched pipes ● along the branch pipe, opposite each plant, there are holes, drippers or small sprinklers. Centre (circular) pivot irrigation ● lightweight aluminium mainline and electrical power cable is laid underground ● mainline leads from source of water and power to centre of circular field ● mainline ends in a valve which is connected to centre pivot ● centre pivot: raised single aluminium irrigation line on wheels with valve at fulcrum (centre) and sprinklers at regular intervals along its length; turns slowly on wheels controlled by gears. Table 5 Advantages of permanent overhead irrigation systems Drip irrigation Centre pivot irrigation Water is spread evenly √ √ Easy to control water delivery √ √ No runoff, thus no erosion or water wastage √ √ Can be used on sloping ground √ √ Weeds are less problematic (ground between plants √ √ does not receive water) Table 6 Disadvantages of permanent overhead irrigation systems Drip irrigation Centre pivot irrigation • fairly expensive • high initial capital outlay (centre pivot equipment) • maintenance is labour intensive • high running costs (pump and equipment maintenance) • well-trained operator needed • not suitable for all crops (i.e. those whose leaves should not be watered) • not suitable for windy days • water loss due to evaporation before water reaches the ground 4.2.2 Moveable systems ● Used to reduce the initial cost outlay. ● Usually need more management and labour during irrigation season. Quick-coupling straight-line system ● Construction: ● main line laid and buried across centre of field (plastic or aluminium) ● branch/sprinkler lines attached to valves/hydrants at intervals along mainline, at right angles ● quick-coupling 6 m branch lines (lightweight aluminium) are laid above ground, linked with quick-coupling clamps to any length required ● narrow, perpendicular riser pipes are positioned at intervals along branch lines with sprinkler nozzles fitted at the top. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 141

Unit 2 XX ● Functioning: ● water is pumped from water source to main line ● several branch lines can be attached to mainline (depending on amount of water, pump strength, field length) ● several sprinklers may be used (depending on amount of available water, pressure-build in piping by pump) ● water pressure causes water to shoot out of sprinklers which makes them turn. ● Advantages: ● most economical and basic sprinkler irrigation system ● no runoﬀ, thus no erosion and water wastage ● water is spread evenly ● easy to control water delivery ● can be used on sloping ground ● less labour intensive than flood irrigation. ● Disadvantages: ● high initial capital outlay (equipment) compared with flood irrigation, but cheaper than permanent or centre pivots ● high running costs (pump and equipment maintenance) ● labour intensive (two people needed to move branch lines to new part of field) ● not suitable for all crops (i.e. those whose leaves should not be watered) ● not suitable for windy days ● water loss due to evaporation before water reaches the ground. 5 Reasons for and advantages of irrigation scheduling ● Determine correct amount of water for crops. ● Determine right time to supplement natural rainfall for each crop type. ● Ensure optimal crop production. ● Conserve scarce or costly resources (water, electricity). 5.1 Factors affecting an irrigation schedule Soil type ● Sandy soils drain and dry out more quickly than clay soils: ● SO → crops on sandy soils need to be irrigated more frequently than clay or clay loam soils. Climate and weather ● Rainfall: irrigation may be required in addition to rainfall during certain periods. Transpiration and evaporation ● Transpiration: plants grow more quickly at higher temperatures (roots suck up more water and nutrients from soil, moves up through plant by transpiration pull, and by evaporation of water through leaves, called transpiration). 142 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 2 XX ● Evaporation: water in and on the soil can evaporate directly into the atmosphere. ● Evapotranspiration: total loss of water from soil by evaporation and from leaves by transpiration. Factors that affect evapotranspiration ● temperature: evapotranspiration increases with temperature ● humidity: evapotranspiration increases as humidity decreases ● wind: evapotranspiration increases with wind ● crop type: root depth, leaf structure and size varies which aﬀects need for water ● water-loving plants: fast growing, large leafy plants (e.g. sugar cane, spinach and lettuce) ● drought tolerant: smaller leaves, fewer stomata, waxy leaf covering on the leaves to reduce transpiration (e.g. onions, lavender) ● root depth: this varies according to plant types, classified according to root length as short (30–60 cm, e.g. celery), medium (60–120 cm, e.g. pumpkin), long (120–180 cm, e.g. sunflowers) 6 How to determine the moisture content of soils ● Determine root depth of crop (use reference table). ● Determine depth of wetness (use soil auger and tape measure). ● Irrigate again and recheck depth of wetness (first irrigation is over once roots are wet). ● Monitor depth of wetness regularly and irrigate again when soil is wet to half the root depth. 6.1 Methods to determine soil wetness Class A evaporation pan ● Determines amount of evaporation from free water surface as an estimate of water lost by plants through evapotranspiration: ● water lost by evapotranspiration is 50–90% of water lost from free water surface (because soil and plants retain water) ● → by measuring the amount of water lost in the evaporation pan and the amount (say 75%) that is lost from the soil, evaporation can be calculated. Tensiometer ● Measures soil tension or force with which water is held in soil by soil particles (in kilopascals, kPa): ● consists of plastic body tube with ceramic cup at bottom end and vacuum gauge at top ● → cup allows water to flow into or out of tensiometer when placed at root depth. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 143

Unit 2 XX Neutron moisture meter (NMM) ● Consists of probe, cabling and a logger which records measurements: ● make long narrow hole in soil with soil auger, fit with thin-walled aluminium tube (or thicker PVC tube) ● probe inserted into tube which is in close contact with surrounding soil ● → probe emits fast neutrons and measures the number deflected back to it, which is proportional to water in ~50 cm area around probe. ● Probe must be calibrated for where it is to be used. 144 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 XX Soil drainage, cultivation and crop rotation 1 The term: soil drainage ● Soil drainage ● = natural or artificial removal of surface and subsurface water from an area ● either excess irrigation water or water that results from high water table. ● Factors to consider before draining soil: ● eﬀect on other water supply, e.g. dry up nearby water source ● eﬀect on local wild plants and animals: if they prefer waterlogged conditions, may not find another suitable home and die out; pest numbers may increase if they were previously eaten by local inhabitants. 1.1 Different types of soil drainage systems A farmer should consider the following before draining an area: ● whether it will be surface or subsurface drainage ● type of drainage systems to be used ● where the water will be drained to ● what will be done with the excess water. Surface drainage ● Open ditch drainage ● uses slope of the land ● furrows are dug down slope of land so that water can be drained to lower ground ● suﬃciently long and wide furrows needed to drain oﬀ all water. ● Ridge and furrow drainage ● used on relatively flat ground (< 3º gradient) ● ridges and furrows along length of field with drainage ditch perpendicular to field ● crops planted on ridges between furrows ● water can be diverted into natural waterways, fish ponds, shallow crop basins. Subsurface drainage ● Increases surface runoﬀ → reduces amount of water going into soil. ● Increases drainage rate → lowers water table → increases dry soil depth above table. ● Two types of subsurface drains: ● pipe drains – water seeps in through holes in pipes below soil surface, then drained away; suited to deep permeable soils, and heavy (clay) or poorly drained soils; backfill is a major cost but crucial to eﬀectiveness; amount of backfill governed by soil type and permeability, depth of backfill, and trench width. ● interceptor drains – installed across direction of water flow near interface between flat and sloping land; pipes laid at base of trench and back filled with permeable material which intercepts water flowing from upslope; water delivered to drainpipe which leads to outflow. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 145

Unit 3 XX 1.2 Factors to consider before installing a pipe drainage system ● Soil suitability: ● determine the soil permeability (soil survey, preferably during winter) to estimate drain spacing and depth; sandy, loam, and some well-structured clay loam soils are suitable. ● Materials to use: ● cost and ease of installation should be considered; plastic pipes are light and easy to work with, clay pipes are heavy and easily damaged; size of holes in pipe is also important. ● Material around pipe (backfill): ● allow movement of water from surrounding soil to pipes. ● Installation method: ● should be on grade and of high quality; use correct spacing of drainage lines (depends on soil permeability); install drainage lines with grade (slope). 2 Primary and secondary soil cultivation: aims and differences ● Soil cultivation or tillage: ● practice to improve soil condition before establishing crops ● must first analyse soil to determine best type of cultivation. ● Aims of soil cultivation: ● killing and removal of weeds ● mixing in of organic matter and fertiliser ● burying or mixing crop residue. Table 7 Comparison of primary and secondary cultivation Primary cultivation Secondary cultivation • deeper and more thorough • shallower • produces rough textured soil • produces smoother surface finish • loosen soil and mix in fertiliser and/or plant • shape planting rows, prepare seed beds and material provide weed control Common implements used for soil cultivation ● Primary cultivation – ● mouldboard plough: ● single blade/share ploughs one furrow at a time, cuts soil and turns it over ● disc plough: ● breaks soil and cuts plants with blade/disc (2-20), pulled by tractor ● subsoiler: ● blade/tine cuts deeper than other types, does not remove covering plants, pulled by large tractor ● digging forks and spades. 146 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 ● Secondary cultivation – ● harrow: ● used to prepare seedbeds, eradicate weeds, flatten soil; drawn by draught animals or tractors; disk (two rows of small discs) and spiked harrows (triangular or zigzag shape with spikes) used to loosen soil ● field cultivator: ● used to prepare seedbeds and eradicate weeds; uses spring-mounted steel shanks to shatter soil clods ● crumbler rollers and rakes ● inter-row cultivation: e.g. inter-row cultivators, hoes ● land forming: e.g. ridgers, hoes. 3 Different types of soil cultivation systems Disadvantages of soil cultivation ● tractors and draught animals compact soil surface → leads to runoﬀ and erosion ● leaves the soil bare, which leads to erosion ● plough pans (hard surfaces) can develop below the surface, which causes waterlogging and root rot/water shortage for plants. No-tillage cultivation system ● used by some farmers due to disadvantages of cultivation ● no ploughing so soil is not loosened or turned over ● plant seeds between leaves and stems left from previous crop ● either make furrows with a hoe and plant by hand or use no-tillage planters ● weeds can be left growing on the soil; kill weeds by slashing or mowing and then leaving on surface, or using herbicides. Intensive cultivation or tillage system ● leaves <15% crop residue ● involves multiple operations with implements (mouldboard and disc ploughs). Conservation cultivation or tillage system ● consists of no or minimum till which leaves minimum of 30% crop residue ● slows water movement, which reduces amount of soil erosion ● keep plant stubble on land = prevents erosion, high soil temperatures, evaporation. Strip cultivation system ● combines conventional tillage (soil drying, warming benefits) with advantages of no- till cultivation ● uses minimum tillage and only disturbs planting area ● labour intensive and uses special equipment. Slash-and-burn cultivation system ● involves cutting and burning of forests or woodlands by hand to create fields ● slash is what has been cut down, remaining ash acts as soil fertiliser. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 147

Unit 3 4 The concept: crop rotation ● Growing diﬀerent crops in sequence in the same field over a number of years: ● sub-divides field (into 4) and plant diﬀerent family of crops on each piece of land ● swap crop families and land sections every year ● after four years, same crop is grown on original patch. ● Advantages: ● helps soil fertility (diﬀerent plants use diﬀerent soil minerals), reduces plant pests (weeds and insects cannot establish themselves). ● Compare with crop monoculture (replant same crop species in same field every year): ● increase in crop-specific pests and diseases ● exploits soil root zone which depletes nutrients and decreases root development. 4.1 Factors to consider when planning a crop rotation programme ● Profitability: ● select crops that are in demand; understand current market trends and production costs. ● Pest management: ● Manage and control crop pests (weeds and insects); know what types of pests are prevalent and how to combat them; consider pests when designing layout of crop rotation land (barrier strips around crops can prevent spreading of weeds). ● Soil moisture and fertility: ● plant suitable crops for soil type; analyse soil moisture and fertility ● Residue management: ● low residue carryover (e.g. from peas) can lead to wind erosion concerns; high residue crops (e.g. wheat) can lead to excessive residue build-up, resulting in direct seeding problems the following season. ● Crop choice: ● plant diﬀerent families in diﬀerent sections; consider functions and needs of diﬀerent crop groups (e.g. nitrogen consumers vs. nitrogen fixers); important to include legumes and companion crops. ● Legumes: ● root nodules contain Rhizobium bacteria which fixes nitrogen in the soil; leave roots in the soil after harvesting to add nitrogen to the soil. ● Companion crops: ● crops that can be grown together for their mutual benefit, e.g. ● maize stem provides beans with climbing support and beans provide maize with nitrogen; practice called companion planting or intercropping. 148 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 3 Advantages ● assists with pest and weed control ● prevents soil from building up negative reactions to specific crops ● improved soil quality, better nutrient distribution, and increased biological activity ● variety of crops produced throughout the year ● decrease financial risk ● peak labour times can be reduced ● balance the production of crop residues. Disadvantages ● requires more knowledge and greater management skills than monoculture ● skill required to choose rotations and recall which crop to plant next ● mechanisation is more diﬃcult ● may not allow for maximum profitability (limited acreage of most profitable crop). © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 149

Unit 4 XX Greenhouses, hydroponics and aquaculture 1 The concept: greenhouse ● Lightweight structure enclosed by transparent covering in which plants are grown: ● elements (e.g. temperature and moisture levels) are controlled to ensure optimum growing conditions for particular plant or crop ● expensive to construct and manage ● used for high-value cash crops, e.g. ● ornamental pot plants, flowers, tomatoes and cucumbers. 1.1 Use of greenhouses for production of high-value cash crops Advantages ● crops protected from natural elements and large pests ● spoilage is minimised while output is maximised → improves profitability ● crops can be cultivated out of season due to temperature control ● extends growing season and allows farmers to produce out-of-season crops → increases profitability ● can grow crops that would not normally thrive in an area ● quality of crops improved. Disadvantages ● high set-up cost for material and labour (e.g. bank loans with interest charges) ● high level of management competence required ● severe hail- and/or windstorms can result in costly damage ● costly and intensive pest and disease control measures required (optimum conditions often encourage small insects). 1.2 Materials that farmers use to construct greenhouses Larger commercial greenhouses are usually tunnel-shaped with a frame made of plastic or aluminium piping. The frame is covered with transparent film plastics. ● Covers are made of cheap polyethylene (PE) or polyvinyl chloride (PVC) materials ● light transmission properties comparable to glass ● PE is UV protected, PVC will last up to five years ● → can be used with light and cheap frames. ● Greenhouse tunnels have door at each end for convenience and ventilation ● sophisticated greenhouses = greater control over conditions ● heating → heating systems for use in cold climates ● circulation → fans for air circulation. Greenhouses with ● ventilation → door, roof or eave vents or hinged flaps to computerised automatic aid ventilation environmental control ● cooling → evaporative cooling apparatus, shading apparatus = even greater control over conditions. materials, paint on covering. 150 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 1.3 Factors to consider in the location of a greenhouse ● Environmental factors: ● local climatic conditions: ● hot areas will require cooling, cold areas need heating, occurrence of storms and hail determine building materials ● availability of water: ● crucial since impermeable plastic covering keeps out rain ● sunlight: ● needs full sun (especially morning sun when plants begin food production process), north/south orientation of long axis is best ● drainage: ● build where it is raised above surrounding area. ● Markets: ● should be close to markets else transport costs become high. ● Power: ● nearby electricity source needed (for sensors, computer equipment, automatic fans and vents, irrigation system). ● Labour: ● need a nearby source of suﬃcient labour. ● Space: ● suﬃcient space for storage area, ablutions for workers and work area. 2 The concept: hydroponic production systems ● This is a method of growing plants in tightly controlled greenhouses in a medium without soil: ● plants grown in inert medium for anchorage of the roots ● soluble nutrients in water flows through inert medium. 2.1 The benefits or advantages of hydroponic production systems ● crops can be grown where there is no soil, or the soil is too poor to support optimum production ● reduced or no soil preparation ● water eﬃcient closed system (uses 5% water vs. normal farm) ● conserves nutrients (those not used are re-circulated) ● high yields due to optimum growing conditions ● uniform production ● high quality crops that require little washing ● can be used to improve nutritional value of vegetables ● reduced soil pollution with fertilisers and pesticides. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 151

Unit 4 2.2 Inputs for hydroponic systems Mediums Mediums are required to support plants and provide aeration. ● Pumice and perlite: ● imported and costly volcanic rock products ● → pumice is lightweight ● → perlite is lightweight and spongy, similar to vermiculite but holds more air and less water. ● Vermiculite: ● superheated mineral (mica) = light, porous, holds a lot of water and nutrients. ● Expanded clay (or ex-clay): ● baked-clay pellets = porous, lightweight, do not compact, reusable after washing. ● Plant fibres: ● coir (or coco peat), wood fibre, peat moss, sawdust, straw bales. ● Inert soil materials: ● sand, gravel and brick shards = provide good anchorage, but do not hold a lot of water or nutrients. Nutrients ● Nutrient solutions contain specifically balanced soluble nutrients at specific concentrations for diﬀerent crops BUT ● pH of water must be controlled to ensure nutrient solubility and availability. Containers ● Required to hold medium and nutrient mixture, e.g. ● plastic or concrete plant containers, trenches lined with plastic. 2.3 Open and closed systems in hydroponic production Open (run-to-waste) hydroponic system ● simplest hydroponic system ● also known as open static hydroponic system ● plants are grown in containers ● micro-tubes feed water and nutrients into containers daily. Closed (or continuous flow) hydroponic system ● more sophisticated hydroponic system ● also known as recirculating trench hydroponic system ● plants grow in trenches with a slope of 1:100 from beginning to end ● elevated tank stores nutrient solution which flows through trench by gravity, past the roots to endpoint reservoir ● water is pumped back to elevated tank from endpoint. 152 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 Table 8 Advantages and disadvantages of open hydroponic production system Advantages Disadvantages • cheaper to erect • requires more labour to operate • requires less skill • wastes more water and nutrients • more costly to maintain (nutrients are not • easier to control spread of disease recycled) 2.4 Production differences between hydroponic and open field systems Hydroponic systems: ● more expensive to set up ● require a high level of technical expertise and management ● require less space to produce the same amount of crop ● higher production per hectare ● better security of production (climate controlled and fewer pests) ● higher quality product ● soil quality is not important (deficiencies rectified through nutrients in water solution) ● high costs thus only used for high-value cash crops. 3 The concept: aquaculture Aquaculture is the controlled production of aquatic living organisms: ● practised in the sea (marine aquaculture) or in fresh water (fresh water aquaculture) ● produces wide variety of fish for human consumption ● supplies > 30% of seafood consumed worldwide: ● > 90% produced in Asia ● < 0,5% produced in Africa. 3.1 Common aquaculture farming species in South Africa Freshwater aquaculture in South Africa ● Normally carried out in earthen ponds and dams, or raceways, or in recirculating systems: ● = limited by supply of suitable water (inland rivers are often polluted) ● In SA, takes place in Limpopo, Mpumalanga lowveld, northern KwaZulu- Natal, and more recently in the Western Cape. ● Largest income source: ● = ornamental fish industry, e.g. goldfish and koi carp. ● Largest food producer: ● = rainbow trout. ● Other species: ● = shrimp, African catfish and tilapia. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 153

Unit 4 Marine aquaculture in South Africa ● Low production volumes but fast developing sector: ● → normally farmed on raft or long lines, or in recirculating systems. ● Major products: ● = abalone (largest amount, mostly exported to the East), oysters ● Largest food producer: ● = mussels. ● Other species: ● = seaweed, spotted grunter, red roman, cob and yellow tail. 3.2 Structures for housing marine and freshwater species Freshwater aquaculture structures Fish farmed in freshwater ● = Brown trout (Salmo trutta), Rainbow trout (O. mykiss), common carp (C. carpio) and African catfish (Cl. gariepinus). Structures used: ● Earthen ponds, dams or raceways: ● earthen ponds and dams: constructed in streams and rivers or alongside them (avoids flooding, requiring pump) ● raceway: water flows between series of ponds or dams built in river or stream. ● Recirculating systems: ● only used away from natural water routes: ● water pumped from source into fish dam, removed at other end, filtered and treated, pumped back to start for recirculation ● expensive to construct, requires expertise and maintenance ● used where water is not plentiful, reduces pollution of rivers. Marine aquaculture structures Fish farmed in marine structure ● = Cob, tilapia, white stumpnose, shellfish. Structures used: ● Long-lines: ● used in shallow seas, estuaries or lagoons: ● consists of long, horizontal nylon ropes stretched across water surface, fixed with floats ● vertical lines hang down from horizontal long-line at intervals; requires sea depth of 5–20 m (no pollution, lots of algal foods). ● Rafts: ● floating structures constructed of wood, plastic and polystyrene: ● act as walkways and floats for long-lines. 154 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Unit 4 ● Cages: ● are attached under rafts and float in the water ● → monoculture of fish (Cob and tilapia) are intensively fed and raised in these. ● Recirculating systems: ● = similar to recirculating systems for fresh water agriculture ● found close to the coast, pump and circulate seawater, raise sea fish (white stumpnose) or shellfish. 3.3 Description of fish culture systems Intensive fish culture systems Large numbers of fish or other aquatic animals are raised in confined spaces: ● nutrients supplied as formulated feed (balanced diet) ● water quality monitored and managed regularly. ● Open through flow system: ● water brought from source (dam or river), enters and flows through fish-raising ponds or dams, leaves to enter river system and flow away ● cheap to set up, less likely to cause disease in the fish. ● Closed recirculating system: ● water enters fish-raising dam or pond, circulated through, collected and filtered and/or purified, reused in the dam ● more costly to set up, can recirculate disease ● suitable for areas with limited quality water supply, reduces pollution of rivers. Extensive fish culture systems Fish (or other species like shrimps) are farmed at low densities in natural still dams or ponds ● either not fed at all or provided with some supplemental feeding ● location must have favourable climate and unlimited space (rural areas) ● monoculture aquaculture system: ● only one species of fish or other aquatic species is kept. ● Unbalanced system: ● some food wastage, water quality may be compromised as waste levels (detritus) build up. ● Polyculture aquaculture system: ● includes integrated agriculture-aquaculture systems (IAA) ● farm with more than one species to obtain optimal production and balanced environment ● uses all available food resources in a pond or dam, and preserves water quality. ● Integrated Agriculture-Aquaculture systems (IAA): ● intensive animal farming is combined with aquaculture (fish) ● wasted food and excrement (manure) from farm animals used to feed fish. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 155

Unit 4 3.4 Basic requirements for aquaculture farmers to achieve high yields ● Good location: ● ensure location has a slope (so that water can flow without a pump) and suitable climate (growth slows down if it is too cold). ● Good water supply: ● requires suﬃcient high quality water. ● Reliable power supply: ● required for pumps, filters and/or heaters ● → erratic electricity supply can slow growth or even kill fish. ● Good quality feed: ● poor nutrition will slow growth and cause deficiency diseases. ● Good planning and support: ● plan in conjunction with aquaculture experts, e.g. ● University of Cape Town, Rhodes University, the Department of Agriculture. ● Relevant knowledge and skills: ● farmers need – ● knowledge of fish biology, ● experience in aquaculture husbandry, ● competence at harvesting and processing ● marketing and sales skills. ● Good species: ● choose correct species for prevailing climatic, managerial, nutritional and housing conditions ● choose good strains. 3.5 Factor that limit the selection of aquaculture species ● geographic location (influences choice of species, climate, average temperature) ● water supply (amount and quality) ● available capital ● expertise and training ● availability of services (electricity, proximity to expertise and food supplies) ● market location (or airport for export produce). 156 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

X 14 Topic XX Unit Topic questions ● Answer the questions below. ● Give yourself one hour. ● Check your answers afterwards and do corrections. 1 Name five characteristics to consider in a soil survey. (5) 2 Define precision farming and state four advantages of this method. (6) 3 Name three sources of groundwater. (3) 4 Refer to the diagram below of diﬀerent irrigation systems and fill in the missing words/phrases indicated by (a) – (c). (3) Irrigation systems Flood irrigation (b) Furrow (a) Permanent systems Moveable systems • Drip irrigation Quick-coupling Variations: (c) • Dragline • Gun stand and gun • Travelling irrigation 5 Describe a quick-coupling straight-line irrigation system, with special reference to its construction. (5) 6 Provide three reasons for and advantages of an irrigation schedule. (3) 7 Name two types of surface drainage and describe briefly the one best suited to relatively flat land. (5) 8 Name two implements used in primary cultivation. (2) 9 Briefly describe the no-tillage method of cultivation. (4) 10 Name two types of crops that should be included in a crop rotation programme. (2) 11 Name five factors to consider when deciding the location for a greenhouse. (5) 12 Describe hydroponics and name the three major inputs required. (5) 13 Briefly discuss aquaculture in South Africa. Mention the two types of aquaculture, where they are carried out and state the largest income source of each type. (6) 14 Explain the main diﬀerence between intensive and extensive fish culture systems. (4) 15 Name two basic requirements for aquaculture farmers to achieve high yields. (2) © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 157

X 14 Topic XX Unit Topic questions 16 Provide the word or phrase that best describes the following statements: a The movement or supply of water from its source to the site of growing crops. b The removal of the thin top layer of soil evenly over a large area, caused by strong winds or heavy rain, in an area with little or no vegetation. c Method in which a field is subdivided and diﬀerent crops are grown in sequence over a number of years. d Involves cutting and burning of forests and woodlands by hand to create fields for planting crops. e The controlled production of aquatic living organisms, mainly for human con- sumption. f A cheap, UV-protected material with good light transmitting properties that is used to construct greenhouses. g Crops that are typically grown in greenhouses due to their profitability. h The simplest hydroponic system in which plants are grown in containers fed by microtubes. i An instrument used to determine soil wetness which consists of a probe con- nected to a logger. (10 1 = 10) Total: 70 158 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

1X Topic XX Unit Answers to Topic questions Topic 1 Answers 1 a Molecule: can be broken down chemically into the elements of which they are composed. Example: carbon dioxide, water, sodium chloride, etc. b Isotopes: atoms of the same element with diﬀerent atomic weights. Example: chlorine. c Valence electron: outermost electrons around an atom. 2 The atom has a small, positively charged core called the nucleus. The atom is electri- cally neutral and consists of: 1) electrons – negatively charged particles contained in a large outer volume called an electron cloud; 2) protons – positively charged parti- cles concentrated in a small inner volume that contain most of the mass of the atom; 3) neutrons – electrically neutral and occur in the nucleus. 3 a alkali-earth metal b fluorine / chlorine / bromine / iodine 4 a covalent bonding b oxidation number c chemical formula d polar e hydrogen bonding 5 b 6 Hydrogen bonds that hold water molecules together are quite strong. But covalent bonds between atoms in a water molecule are stronger. Thus hydrogen bonds often break and reform which provide water’s ability to flow. 7 a carbon, oxygen b 2 of Fe, Mn, B, Mo, Cu, Zn, Cl, Co 8 Plants use CO2 and H2O to build complex organic compounds. They are excreted by animals during respiration. 9 a alcohol b aldehyde c amide d sugar © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 159

X 13 Topic XX Unit Answers to Topic questions 10 a CH4 b methanogenesis c most abundant 11 Propanol, primary 12 a A fatty acid is a long chain carboxylic acid. Saturated fatty acids contain only single C-C bonds, whereas unsaturated fatty acids contain 1 or more C-C double bonds. b cis isomer c Name any 4 of these: energy storage, waterproof coverings, main component of cell membranes, protection, function as hormones. 13 amino NH2 group carboxyl H C COOH group R 14 An amino acid that cannot be synthesised by the organism (usually humans) and must be supplied in the diet daily, typically from meat and dairy products. 15 ● takes place mainly in the youngest plant tissues, i.e. meristematic tissues ● nitrogen is obtained from soil ● carbon is obtained from carbohydrates produced during photosynthesis ● N and C are contained in storage carbohydrates in seeds ● amino acids are formed in seeds and leaves (mainly in leaf chloroplasts) 16 a monosaccharides, glycosidic b condensation / dehydration c 6, fructose d photosynthesis e maltose f energy g walls Total: 70 160 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

1X Topic XX Unit Answers to Topic questions Topic 2 answers 1 Clay – smallest soil particles; Silt – in between size of clay and sand particles; Sand – largest soil particles 2 Name any 3 of: aggregate formation and stability, climate, tillage, electrostatic forces 3 Discuss any 3 of: ● amount of organic matter ● usually topsoil (i.e. A-horizon) is dark or black ● presence of compounds and elements ● iron oxides: yellowish-brown to reddish colour ● manganese oxides: purplish-black soil colour ● calcium carbonate: white ● carbon compounds: black ● drainage ● poor drainage results in light grey colour or rust-like spots (mottles) ● referred to as bleached or washed out ● leaching ● loss of iron compounds and coloured minerals results in light colour 4 oxygen, carbon dioxide, nitrogen (most important) 5 a gravitational, capillary, hygroscopic b gravitational (i), capillary (iii, v), hygroscopic (ii, iv) c loss d any 4 of transpiration, evaporation, interception, runoﬀ and drainage 6 a Vegetation and cloud cover intercepts direct sunlight, and cloud cover can also insulate soil from temperature changes. b This can be measured by comparing temperatures under a tree with a bare soil OR the temperature between rows of healthy crops with nearby bare soil. 7 Topsoil: topmost layer, high proportion of organic matter Subsoil: just beneath the topsoil, low in organic matter 8 Binomial classification system. List any 3 of: ● organise and facilitate knowledge about soils ● understand the relationship among diﬀerent soils ● establish groups or classes of soils for practical purposes ● predict the behaviour of diﬀerent soils ● identify the best uses of soils ● estimate agricultural productivity potential ● transfer information to similar soils in other locations © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 161

X 13 Topic XX Unit Answers to Topic questions 9 Soil colloids are very small particles of either organic or inorganic matter that are found in soil. They carry an electrostatic charge and determine the physical and chemical properties. Examples: any 2 of phyllosilicate clay minerals, non-crystalline silicate clays, oxides. 10 Active acidity is the concentration of H+ ions in soil and water mixture; reserve acid- ity is the concentration of H+ ions attached to clay and organic matter and not dis- solved in solution. 11 List any 4 of ● monitor soil pH (take several soil samples in your field) ● test irrigation water ● apply sulphur or gypsum ● do not over use compost and animal manure ● irrigate to leach salts in drier areas ● cover soil with mulch during summer months ● do not over use lime soil 12 ● step 1: plants absorb phosphorus from soil, animals obtain phosphorus by eating plants ● step 2: plant and animal matter are decomposed by micro-organisms ● step 3: micro-organisms release phosphorus into the soil (i.e. mineralisation) ● most phosphorus is unavailable as it is insoluble or bound to soil particles ● micro-organisms release some of this insoluble phosphorus (i.e. solubilisation) 13 ● Rhizobium bacteria penetrates the roots and forms nodules in the tissues ● plants receive nitrogen extracted from the air ● bacteria receives water and nutrients from the host plant ● symbiosis is reduced by nitrogen fertilisation, high soil acidity and temperatures 14 ● decomposition by aerobic micro-organisms → release of carbon dioxide (CO2) ● decomposition by anaerobic micro-organisms → release of methane (CH4) ● methane contributes much more to global warming than carbon dioxide ● burying organic matter in landfills contributes to global warming ● composting kitchen waste is preferable and returns organic matter to soil Total: 70 162 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

1X Topic XX Unit Answers to Topic questions Topic 3 Answers 1 b 2 ● production and renewal of almost all the atmospheric oxygen ● provision of food for all plants and animals ● production of fossil fuels (coal, natural gas, oil) from plant and animal remains ● reduction of CO2 in the atmosphere 3 Ca, Mg, S 4 1b, 2a, 3c 5 ● done when crop is already growing ● leaf sample taken to laboratory where it is washed, dried and stored ● representative sample taken at a certain time of the year ● pick 10–20 young, mature healthy leaves (at least 10 undamaged) before 10:00am ● do not wash, place in clean plastic bag and deliver to laboratory immediately 6 List any 2 of: application of organic matter, soil air, moisture content, soil type and pH, factors that are detrimental to soil microbes 7 a) inorganic fertiliser; b) green manure; c) parthenocarpy; d) integrated weed control; e) Bt maize; f) anther; g) dormancy; h) stigma 8 Mass of K in 100kg mixture = [1 / (3+2+1)] of 22 = [1/6] of 22 = 3,7% 9 LAN or limestone ammonium nitrate 10 KCl 11 ● physical eﬀects – maintains and increases the organic content of soil ● chemical eﬀects – contains almost all plant nutrients, but some may be in insuﬃcient quantities ● biological eﬀects – soil bacteria are added to soil 12 ● uniform distribution of fertiliser over planting area ● usually worked into the ground ● used for crops that cover the land ● fertilisers that dissolve slowly require deep incorporation 13 ● process by which pollen is transferred in plants, enabling fertilisation and sexual reproduction ● pollen carried from anther to stigma; pollen grain grows downwards towards the ovary and fertilises an ovule ● ovary forms the fruit, fertilised ovules develop into seeds © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 163

X 13 Topic XX Unit Answers to Topic questions 14 Asexual reproduction in plants is the reproduction from pieces of the parent plant other than the seeds. 15 bulbs, tubes, rhizomes, stolons/runners 16 a) stem and bud; b) two stems 17 Form of cross-pollination in which pollen from flower of one cultivar is placed on the stigma of a flower of a second cultivar to breed a hybrid plant that is better than both the parent cultivars. 18 dodder, witchweed 19 Birds: pass seeds through their digestive tract, which are deposited in their faeces Machines: farm vehicles transfer seeds stuck in their tyre treads OR seeds present in soil are exposed to light and air by ploughs during cultivation (any one of these) 20 a) ii; b) iii; c) ii Total: 70 Topic 4 Answers 1 ●soil texture ● soil depth ● rockiness of soil ● amount of soil erosion ● slope 2 Precision farming: ● modern method of crop farming management, uses traditional soil survey and ultramodern techniques ● basic principle to manage small areas within fields and not whole field ● farm with most productive crop to get best return (profit or yield) per hectare of land Advantages: ● optimal production ● less damage to the environment ● sustainability of production ● healthier food, and traceability of foods produced and consumed 3 Name any 3 of: spring, vlei, well, borehole 4 a basin b overhead / sprinkler c centre pivot 164 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

1X Topic XX Unit Answers to Topic questions 5 ● main line laid and buried across centre of field (plastic or aluminium) ● branch/sprinkler lines attached to valves/hydrants at intervals along mainline, at right angles ● quick-coupling 6 m branch lines (lightweight aluminium) are laid above ground, linked with quick-coupling clamps to any length required ● narrow, perpendicular riser pipes are positioned at intervals along branch lines with sprinkler nozzles fitted at the top 6 Name any 3 of: ● determine correct amount of water for crops ● determine right time to supplement natural rainfall for each crop type ● ensure optimal crop production ● conserve scarce or costly resources (water, electricity) 7 open ditch drainage, ridge and furrow drainage Ridge and furrow drainage: ● ridges and furrows along constructed along the length of the field with a drainage ditch perpendicular to field ● crops planted on ridges between furrows ● water can be diverted into natural waterways, fish ponds, shallow crop basins 8 Name any 2 of: mouldboard plough, disc plough, subsoiler, digging forks, spades 9 ● no ploughing so soil is not loosened or turned over ● plant seeds between leaves and stems left from previous crop ● either make furrows with a hoe and plant by hand or use no-tillage planters ● weeds: can be left growing on the soil; killed by slashing or mowing and then leaving on surface, or using herbicides 10 legume family, companion crops 11 ● environmental factors (can also say: local climate, availability of water, sunlight or drainage) ● markets ● power ● labour ● space 12 ● method of growing plants in tightly controlled greenhouses in a medium without soil; plants grown in inert medium for anchorage of the roots; soluble nutrients in water flows through inert medium ● Inputs: medium, nutrients, container. © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 165

X 13 Topic XX Unit Answers to Topic questions 13 freshwater aquaculture: carried out in earthen ponds and dams, raceways, recirculating systems; largest income source is ornamental fish industry (goldfish and koi carp) marine aquaculture: carried out on raft or long lines, or in recirculating systems; major product is abalone 14 Intensive system: ● large numbers of fish or other aquatic animals are raised in confined spaces ● nutrients supplied as formulated feed (balanced diet) Extensive system: ● fish (or other species like shrimps) are farmed at low densities in natural still dams or ponds ● either not fed at all or provided with some supplemental feeding 15 Name any 2 of: ● good location ● good water supply ● reliable power supply ● good quality feed ● good planning and support ● relevant knowledge and skills ● good species 16 a irrigation b evapotranspiration c crop rotation d slash-and-burn cultivation e aquaculture f polyethylene / PE g high-value cash crops h open / run-to-waste hydroponic system i neutron moisture meter / NMM Total: 70 166 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

Exam Practice AGRICULTURAL SCIENCES Paper 1 ● TIME: 2.5 HOURS ● 150 marks SECTION A QUESTION 1 1.1 Various options are provided as possible answers to the following questions. Choose the most correct answer and write only the letter (a–d) next to the question number. 1.1.1 Components of the atom that contains most of its mass: a) Neutrons b) Electrons c) Nucleus d) Protons 1.1.2 An organic compound that contains a characteristic OH group: a) Carboxylic acid b) Alcohol c) Amine d) Phenol 1.1.3 The structural level of a protein responsible for the local arrangement: a) Primary structure b) Secondary structure c) Tertiary structure d) Quaternary structure 1.1.4 Carbohydrates serve the following functions in animals: a) Act as storage food b) Act as a hormone c) Provide frictionless movement d) All of the above 1.1.5 The most convenient laboratory method for soil analysis: a) Hydrometer method b) Sausage method c) Feel method d) Pipette method 1.1.6 This soil colour indicates the presence of iron compounds: a) Grey b) Red c) Yellow d) Light colour 1.1.7 The diagnostic topsoil horizon that is thin and low in organic matter: a) Melanic A b) Organic O c) Orthic A d) G horizon © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 167

Exam Practice 1.1.8 An organism that converts nitrites to nitrates in soil: a) Nitrosomas b) Denitrification bacteria c) Nitrogen-fixing bacteria d) Nitrobacter (8 x 2 = 16) 1.2 The following statements are FALSE. Change the bold word(s) to make each statement TRUE. Write only the words next to the question number. 1.2.1 Chlorine is an example of a noble gas. 1.2.2 Soil air contains more oxygen than atmospheric air. 1.2.3 The E-horizon is the surface horizon which contains topsoil. 1.2.4 Organic soil colloids carry a net positive charge. 1.2.5 More green matter is required when making a compost heap. (5 x 2 = 10) 1.3 Write the agricultural word/ phrase for each of the following descriptions. 1.3.1 Type of bonding exhibited by sodium chloride 1.3.2 Process by which the principal component of natural gas is produced 1.3.3 A long chain carboxylic acid that contains two or more double bonds 1.3.4 Collection of soil aggregates bound together by natural processes 1.3.5 Force that enables water to travel up the stem of a plant 1.3.6 A process that does not require oxygen 1.3.7 Important components of cell membranes that possess a strongly polar character 1.3.8 A soil profile with minimal horizontation and a strong influence from parent material 1.3.9 Mass of soil per unit volume in its natural field state (9 x 1 = 9) 1.4 Choose a word/term from column B that matches a description in column A. Write only the letter (A-J) next to the question number. (5 x 2 = 10) COLUMN A COLUMN B 1.4.1 Example of a transport protein A sodic soil 1.4.2 Monosaccharide composed of 4 carbons B haemoglobin 1.4.3 Used to manipulate soil temperature and improve crop production C tetrose 1.4.4 Chlorine-washed soil that contains excess sodium D pentose E row spacing 1.4.5 Fungus that attached to plant roots and enhances phosphorus F mycorrhizae absorption G soil thermometer H actin I Rhizobium J saline soil TOTAL SECTION A: 45 QUESTION 2: BASIC AGRICULTURAL CHEMISTRY 2.1 Water is necessary for life because water is the medium in which all of life’s chemical reactions take place. It nourishes animals, human cells and every plant. 2.1.1 Explain the term valence electron. (2) 2.1.2 Use the number of valence electrons on oxygen and hydrogen to help you construct a Lewis structure of water. (3) 2.1.3 Name and define the type of bonding exhibited by water. (3) 2.1.4 The bonding referred to in (2.1.3) is responsible for one of the unique characteristics of water. Name this characteristic and describe briefly. (4) 168 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Exam Practice 2.1.5 Name 2 other properties of water that make it the ideal medium for living organisms. (4) 2.1.6 Choose the correct word to complete the following sentence: Water is a (polar/non-polar) molecule due to the presence of highly electronegative oxygen atoms. (1) 2.1.7 Explain what is meant by an electronegative atom. (2) 2.2 Amino acids are the basic building blocks of proteins. Their basic structure is shown in the figure below. amino NH2 group carboxyl H C COOH group R 2.2.1 Explain the diﬀerence between essential and non-essential amino acids. (2) 2.2.2 List four essential amino acids. (4) 2.2.3 Proteins are made up of amino acids covalently linked by peptide bonds. Briefly explain how this bond formation occurs. (3) 2.2.4 The side chain, designated by the R group in the figure above, allows proteins to perform several important functions. Name 2 of these functions. (2) 2.3 The formation or synthesis of proteins in plants is vital to their survival. Discuss protein synthesis in plants. (5) [35] QUESTION 3: BASIC AGRICULTURAL CHEMISTY 3.1 The following table shows the basic groupings of organic compounds. Provide a word/phrase that corresponds with (a) – (d). (4) Elements contained in Organic compound Main function compound form structural parts of organisms; (a) C, H, O, N, S, P participate in cell signalling and recognition; act as molecules of immunity Carbohydrates C, H, O major food and energy source Lipids C, H, O, N, S, P (b) storage of organism’s …(d)… information and its (c) C, H, O, N, P conversion into proteins 3.2 Saturated fatty acids play a vital role in nutrition and bodily functions but they should be consumed in moderation. 3.2.1 Name two food items that contain a high proportion of saturated fatty acids. (2) 3.2.2 Name two functions of saturated fatty acids that demonstrate their importance in bodily functions. (4) 3.3 Carbohydrates are essential for energy. 3.3.1 Provide a general formula for carbohydrates. (1) 3.3.2 Name the process that builds carbon atoms from carbon dioxide into monosaccharides. (2) 3.3.3 Name the type of bond that joins monosaccharides together to bond a disaccharide. (1) 3.3.4 Provide a chemical formula for the most well-known monosaccharide. (2) 3.3.5 Name the disaccharide that consists of two glucose units. (2) © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 169

Exam Practice SOIL SCIENCE 3.4 Soil texture is defined as the relative proportions of sand, silt, and clay particles in a mass of soil. 3.4.1 Name the tool that soil scientists and farmers use to classify soil textures. (2) 3.4.2 Name two ways in which soil textural classes may be determined. (4) 3.4.3 Knowledge of textural classes allows farmers to maximise productivity and minimise environmental harm. State 5 factors that are aﬀected by soil texture. (5) 3.4.4 Name the smallest soil particle or separate. (2) 3.4.5 Provide two properties of soils containing a high percentage of this soil separate. (4) [35] QUESTION 4: SOIL SCIENCE 4.1 Soil structure refers to the arrangement of solid parts of the soil and the pore spaces between. The assembly of soil structure can be depicted by the flow diagram below. bound by stack around …..(a)…. bind together each other single soil particles …..(b)….. peds or (c) soil structure 4.1.1 Provide the missing word/phrase indicated by (a), (b) and (c) in the diagram above. (3) 4.1.2 Soil structure is classified according to the three main criteria. Name these criteria. (6) 4.1.3 List four ways in which soil structure can be improved. (4) 4.2 There are three main types of soil water and some of their properties are summarised in the table below. Provide the word/phrase that corresponds to (a) – (e). (5) Gravitational water Capillary water …… (c)…. water found in soil ……(a)….… found in soil ..….(b)……. forms thin films around soil particles held on particle surface by …(d)…. moves through soil due to force of held against pull of gravity by forces gravity cohesion and adhesion forces ……(e)……. (available/ not available) not available to plants as it moves available for plant growth to plants rapidly out of well-drained soil 4.3 Soil water balance reflects all quantities of water added, removed or stored in a given volume of soil during a given period of time. The change in soil water over time is given by the following expression: ΔSm = Sm + P – T – E – I – R – D 4.3.1 State the processes represented by the symbols T and I in the formula. (2) 4.3.2 Explain what leads to the process indicated by the letter “R”. Indicate in your answer what the process designated by “R” is called. (2) 4.3.3 Briefly describe three strategies to limit the eﬀect of process “E”. Indicate in your answer what the process designated by “E” is called. (3) 4.4. Explain the main role of soil micro-organisms and macro-organisms. (2) 4.4.1 State the requirements of soil micro-organisms with regard to air. (1) 4.4.2 List three types of soil micro-organisms. (3) 4.4.3 The decomposition of organic matter by micro-organisms has a significant impact on global warming. Explain this statement. (4) [35] TOTAL SECTION B: 105 170 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Exam Practice AGRICULTURAL SCIENCES Paper 2 ● TIME: 2.5 HOURS ● 150 marks SECTION A QUESTION 1 1.1 Various options are provided as possible answers to the following questions. Choose the most correct answer and write only the letter (a–d) next to the question number. 1.1.1 The process of photosynthesis: a) produces food b) releases energy c) consumes oxygen d) both (a) and (c). 1.1.2 Stomata: a) are passages on leaves that allow the exchange of gases between plants and soil b) are controlled by guard cells c) are open during the day to prevent water loss in succulents d) all of the above. 1.1.3 Which statement about potassium is incorrect? a) It is available as soluble K in salts. b) It is available in rock minerals. c) It can be absorbed to a negative charge on clay particles. d) It is fixed by clay minerals when soil dries out. 1.1.4 Oculation: a) is a type of sexual reproduction in plants b) requires budding onto young plants c) is the joining of the stem of one plant with the stem of another d) is the same as grafting. 1.1.5 Weeds: a) can be selectively removed using herbicides b) provide food to other plants c) can be controlled with mulching d) both (a) and (c). 1.1.6 Integrated pest management: a) tries to establish acceptable pest levels b) does not solve long-term pest problems c) does not involve cultural practices d) none of the above. 1.1.7 Signs of soil erosion include: a) a bare ground with new plant growth b) dams that are filled with mud c) storms d) shallow footpaths. © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 171

Exam Practice 1.1.8 Constructed sources of groundwater are: a) springs and wells b) springs and vleis c) well and boreholes d) vleis and dams (8 x 2 = 16) 1.2 The following statements are FALSE. Change the bold word(s) to make each statement TRUE. Write only the word(s) next to the question number. 1.2.1 Osmosis is the spread of molecules from an area of high concentration to one of low concentration until equilibrium is reached. 1.2.2 Animal manure is slowly available to plants whereas green manure is immediately available. 1.2.3 Oysters are the major product of the marine aquaculture sector in South Africa. 1.2.4 Active nutrient uptake in plants is carried out by transport carrier molecules. 1.2.5 Google Earth is a website that provides satellite imagery which can be used in crop farming. (5 x 2 = 10) 1.3 Write the agricultural word/phrase for each of the following descriptions. 1.3.1 The yellowing of normally green leaves due to a lack of chlorophyll. 1.3.2 An implement used to prepare seedbeds that is drawn by draught animals or tractors. 1.3.3 A hydrated form of calcium sulphate that is used as fertiliser. 1.3.4 The process of improving cultivars by collecting seeds from the best plants. 1.3.5 The process of determining soil characteristics and the quality of soil in order to aid the development of a land-use plan. 1.3.6 A form of flood irrigation that is suitable for growing fruit trees. 1.3.7 This occurs when rainwater runs over the soil surface instead of seeping into the soil. 1.3.8 Superheated mica that is used as a medium for hydroponics. 1.3.9 A system that uses wasted food and excrement from animals to feed fish. (9 x 1 = 9) 1.4 Choose a word/term from column B that matches a description in column A. Write only the letter (A–J) next to the question number. (5 x 2 = 10) COLUMN A COLUMN B 1.4.1 Causes damage to a plant ovary such that the ovule is not A lesser grain borer fertilised. B maize weevil 1.4.2 Pest whose larvae grows in individual grains of a particular C GIS crop and eats it from the inside out. D quick-coupling straight-line 1.4.3 Satellite network that orbits Earth and provides precise system co-ordinates of any location. E coco peat F ablactation 1.4.4 A reusable medium suitable for hydroponics. G micro irrigation system 1.4.5 The most economical and basic sprinkler irrigation system. H GPS I expanded clay J parthenocarpy TOTAL SECTION A: 45 172 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Exam Practice SECTION B QUESTION 2: PLANT STUDIES 2.1 The following picture illustrates the vital process of photosynthesis. Study it carefully and answer the questions that follow. ( a) (b) (c) water 2.1.1 Provide suitable labels for (a), (b) and (c). (3) 2.1.2 Complete the following equation which represents the process of photosynthesis. …(a)… + H2O + sun’s energy → …(b)… + O2 (2) 2.1.3 Where does photosynthesis take place in the leaves? (1) 2.1.4 Name the pigment that provides plants with a yellow, orange or red colour. (2) 2.1.5 Photosynthesis takes place in 2 phases. Where does the dark phase take place? (1) 2.1.6 Where do plants store their food temporarily during the day? (1) 2.2 Briefly state 5 negative impacts of inorganic fertilisers on the environment. (5) © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 173

Exam Practice 2.3 Refer to the figure of a flower below and answer the questions that follow. 2.3.1 Name the non-sexual parts of the flower and indicate the figure labels that correspond to these parts. (4) 2.3.2 Briefly describe the function of the parts named in (2.3.1). (2) 2.3.3 Define pollination. (2) 2.3.4 Provide a label for the parts involved in pollination. (2) 2.4 Name the 4 processes involved in seed germination. (4) 2.5 Name the method used to bring seeds out of dormancy. (1) 2.6 Asexual reproduction in plants is the reproduction from pieces of the parent plant other than the seeds. 2.6.1 Name 3 types of specialised stems and roots that can be used in this form of reproduction. (3) 2.6.2 Explain what happens to these organs at the end of the growing season. (2) [35] QUESTION 3: PLANT STUDIES 3.1 Agricultural biotechnology attempts to understand and manipulate the genetic makeup of organisms for use in the production and processing of agricultural products. 3.1.1 Give another name for genetically modified organisms. (2) 3.1.2 Name 5 new and desirable characteristics of genetically modified plants. (5) 3.1.3 Name the 2 most popular genetically modified crops in South Africa. (2) 3.1.4 Briefly describe 2 disadvantages of genetic modification. (2) 3.2 Biological weed control has been successfully applied to eradicate the prickly pear cactus. Discuss this statement. (5) 3.3 Integrated pest management is a system that uses good cultivation practices based on an ecological approach, combined with chemical and biochemical methods, to control pests. 3.3.1 One of the main principles of IPM is to establish action thresholds. Briefly explain what is meant by this statement. (4) 3.3.2 Outline the 6 steps to follow when implementing such a programme. (6) 174 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

Exam Practice OPTIMAL RESOURCE UTILISATION 3.4. Define soil erosion. (2) 3.4.1 Name 3 types of soil erosion and briefly describe each one. (6) 3.4.2 Name one other important soil characteristic. (1) [35] QUESTION 4: OPTIMAL RESOURCE UTILISATION 4.1 Irrigation is the movement or supply of water from a water source to the site of growing crops to improve their production. The diagram below illustrates one form of irrigation used by farmers. Study it carefully and answer the questions that follow. wall of canal opened so water flows into basin a) b) wall of basin opened so water flows into next basin 4.1.1 Name the type of irrigation illustrated in the diagram. (1) 4.1.2 Provide suitable labels for (a) and (b). (2) 4.1.3 Briefly describe the system named in (4.1.1). (4) 4.1.4 Name one advantage and one disadvantage of this system. (2) 4.2 Water quality is an important criterion to check. Name 3 measurements that can be made in a laboratory to assess water quality. (3) © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook 175

Exam Practice 4.3 Refer to the diagram below which illustrates an agricultural programme. 4.3.1 Name and describe the programme depicted by the diagram. (4) ar 3 year 4 4.3.2 Name the practice that is in direct contrast with (4.3.1). (1) 4.3.3 Name 5 factors to consider when planning such a programme. (5) 4.4 Name 3 aims of soil cultivation. (3) 4.5 A greenhouse is a building used to grow plants. 4.5.1 Explain why a greenhouse may be preferred to growing crops outside in a field. (2) 4.5.2 Discuss the materials required to construct the cover of a greenhouse. (4) 4.6 Define hydroponics. (2) 4.6.1 Name 2 types of hydroponic systems. (2) [35] TOTAL SECTION B: 105 176 © Via Afrika Publishers » Agricultural Sciences 11 Study Guide eBook

X 13 Topic XX Unit Answers to Exam Practice questions AGRICULTURAL SCIENCES Paper 1: Suggested memorandum SECTION A QUESTION 1 1.1.1 d 1.1.2 b 1.1.3 b 1.1.4 d 1.1.5 a 1.1.6 b 1.1.7 c 1.1.8 d 1.2.1 halogen 1.2.2 carbon dioxide 1.2.3 A-horizon 1.2.4 inorganic 1.2.5 brown 1.3.1 ionic bonding 1.3.2 methanogenesis 1.3.3 polyunsaturated fatty acid 1.3.4 peds 1.3.5 capillarity 1.3.6 anaerobic 1.3.7 phospholipids 1.3.8 young soil 1.3.9 soil bulk density 1.4.1 B 1.4.2 C 1.4.3 E 1.4.4 A 1.4.5 F SECTION B QUESTION 2 2.1.1 Valence electrons are the outermost electrons around an atom and the most likely to take part in chemical reactions. 2.1.2 or using straight lines for the 2 O-H bonds. 2.1.3 Hydrogen bonding: a strong, electrostatic attraction between a hydrogen atom and an electronegative atom, e.g. nitrogen, oxygen, fluorine. 2.1.4 Flexibility and flow characteristic ● Hydrogen bonds that hold water molecules together are quite strong ● But covalent bonds between atoms in a water molecule are stronger ● Thus hydrogen bonds often break and reform which provide this property © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 177

X 13 Topic XX Unit Answers to Exam Practice questions 2.1.5 Mention any 2 of: ● Capacity to absorb high levels of heat energy before its temperature is raised ● Release of high amounts of heat energy upon vaporisation of water ● High surface tension 2.1.6 polar 2.1.7 An electronegative atom is one that attracts/pulls electrons strongly towards it. 2.2.1 Essential amino acids cannot be synthesised by the organism. Non-essential amino acids are synthesised by the body from essential amino acids. 2.2.2 List any 4 of: arginine (not for adults), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine 2.2.3 Peptide bond formation occurs between COOH of one amino acid and NH2 of an adjacent amino acid. It occurs in a condensation reaction during which a water molecule is lost. 2.2.4 List any 2 of: allow ligand binding and protein folding, provide catalytic activity, stabilise final conformation. 2.3 Protein synthesis in plants: ● takes place mainly in the youngest plant tissues, i.e. meristematic tissues ● nitrogen is obtained from soil ● carbon is obtained from carbohydrates produced during photosynthesis ● N and C are contained in storage carbohydrates in seeds ● amino acids are formed in seeds and leaves (mainly in leaf chloroplasts) QUESTION 3 3.1 a) proteins; b) major cell membrane constituent; c) nucleic acids; d) heritable 3.2.1 cheese / fatty meats (or any animal fat); coconut oil / chocolate (or any vegetable product) 3.2.2 Name any 2 of: ● provide the appropriate stiﬀness and structure to cell membranes and tissues ● strengthen the immune system ● involved in inter-cellular communication (e.g. protect against cancer) ● involved in the function of cell membrane receptors (e.g. protect against diabetes) ● lung and kidney function, hormone production ● suppress inflammation ● saturated animal fats carry fat-soluble vitamins A, D and K2 which promote good health 3.3.1 Cx(H2O)x 3.3.2 Calvin cycle / carbon reduction cycle 3.3.3 glycosidic bond 178 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

X 13 Topic XX Unit Answers to Exam Practice questions 3.3.4 C6H12O6 3.3.5 maltose 3.4.1 soil textural triangle 3.4.2 How to determine textural class: ● analyse soil composition in a laboratory and use the soil textural triangle ● analyse soil in the field and estimate the soil textural class 3.4.3 Factors aﬀected by soil textural class: ● seed germination ● water holding capacity ● drainage properties ● root development ● pesticide movement 3.4.4 clay 3.4.5 Properties of clayey soils and their implications ● low infiltration rate – when dry, hard clay soils limit seed germination ● poorly drained and aerated – become waterlogged in rainy seasons QUESTION 4 4.1.1 a) soil colloids; b) soil aggregates; c) clods 4.1.2 type/shape, class/size, grade 4.1.3 List any 4 of: ● increase organic content ● green manuring ● reduce or eliminate tillage and cultivation ● avoiding soil disturbance: ● ensure suﬃcient ground cover: ● apply gypsum (calcium sulfate) to irrigated land 4.2 a) macro pores; b) micro pores; c) hygroscopic; d) adhesion forces; e) not available 4.3.1 T is transpiration, I is interception 4.3.2 R is for runoﬀ. This occurs when precipitation rate exceeds water infiltration rate. 4.3.3 E is for evaporation. It can be limited by restricting solar energy from reaching the soil surface, not irrigating frequently, and using deeper irrigations at longer intervals. (mention any 1 of the 3 strategies) 4.4 Soil micro-organisms decompose dead plants and animals, and animal dung. Soil macro-organisms decompose dead organic matter so that micro-organisms can decompose it further. 4.4.1 Soil micro-organisms require oxygen in the air as they are mostly aerobic organisms. © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 179

X 13 Topic XX Unit Answers to Exam Practice questions 4.4.2 Name any 3 of: algae, bacteria, fungi, protozoa 4.4.3 Global warming: ● decomposition by aerobic micro-organisms = release of carbon dioxide (CO2) ● decomposition by anaerobic micro-organisms = release of methane (CH4) ● methane contributes much more to global warming then carbon dioxide ● burying organic matter in landfills contributes to global warming AGRICULTURAL SCIENCES Paper 2: Suggested memorandum SECTION A QUESTION 1 1.1.1 d 1.1.2 b 1.1.3 b 1.1.4 b 1.1.5 d 1.1.6 a 1.1.7 b 1.1.8 c 1.2.1 diﬀusion 1.2.2 liquid 1.2.3 abalone 1.2.4 ion 1.2.5 precision 1.3.1 chlorosis 1.3.2 harrow 1.3.3 gypsum 1.3.4 selection 1.3.5 soil survey 1.3.6 basin irrigation 1.3.7 surface water 1.3.8 vermiculite 1.3.9 integrated agriculture-aquaculture / IAA 1.4.1 F 1.4.2 B 1.4.3 H 1.4.4 I 1.4.5 D SECTION B QUESTION 2 2.1.1 a) carbon dioxide or CO2; b) oxygen or O2; c) chlorophyll 2.1.2 a) CO2; b) carbohydrates 2.1.3 chloroplasts 2.1.4 carotenoid 2.1.5 stroma of chloroplasts 2.1.6 leaf cells 180 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

X 13 Topic XX Unit Answers to Exam Practice questions 2.2 ● environment negatively aﬀected when fossil fuels are burned during their production ● release substances that contribute to acid rain and greenhouse eﬀect ● cause water contamination ● do not add any organic material into the soil, thus organic material is depleted by soil micro-organisms ● contain sulphuric acid and hydrochloric acid which increase soil acidity, thus decreasing nutrient availability and killing Rhizobium, a nitrogen-fixing bacteria 2.3.1 sepal (c); petal (d) 2.3.2 The petals (collectively referred to as the corolla) and sepals (collectively referred to as the calyx) support the sexual parts of the flower. The calyx protects the ovary and the corolla attracts insects to the flower. 2.3.3 Pollination is the process by which pollen is transferred from the anther to the stigma in plants, enabling fertilisation and sexual reproduction. 2.3.4 anther (a); stigma (e) 2.4 Process 1: imbibition, process 2: respiration, process 3: activation of enzyme systems, process 4: radicle emergence and seedling growth 2.5 scarification 2.6.1 Name any 3 of: bulbs, tubers, rhizomes, stolons/runners 2.6.2 The shoots die down and remain dormant in the soil until the next growing season. QUESTION 3 3.1.1 transgenic organisms 3.1.2 Name any 5 of: ● plants that are resistant to diseases, pests and stress ● fruits and vegetables that stay fresh for longer ● plants that possess healthy fats and oils and increased nutritive value ● soybeans with a higher expression of naturally occurring anti-cancer proteins ● higher value-added feed for livestock ● higher fibre extraction rates in paper and pulp industry (lignin modification in trees) 3.1.3 Bt insect resistant maize and Roundup Ready (RR) herbicide-tolerant maize 3.1.4 Name any 2 of: ● Environmental: indiscriminate use of weed killers on herbicide resistant crops ● Health: long-term eﬀects have not been established ● Economic: too costly for small-scale farmers © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 181

X 13 Topic XX Unit Answers to Exam Practice questions 3.2 The cochineal bug has been used successfully to eradicate the prickly pear cacti. The cactus was imported from Central America and covered almost a million hectares of farmland in the Eastern Cape. The bug was bred in laboratories and used to suck sap from leaves which was spread by birds that visited prickly pears for fruit. 3.3.1 IPM programmes first work to establish acceptable pest levels, called action thresholds, and apply controls if these thresholds are crossed. By allowing a pest population to survive at a reasonable threshold, selection pressure is reduced. This stops the pest gaining resistance to chemicals produced by the plant or applied to the crops. 3.3.2 1) Proper identification of pests 2) Learn pest and host lifecycle and biology 3) Monitor the environment for pest population 4) Establish action threshold 5) Choose an appropriate combination of management tactics 6) Evaluate results 3.4 Soil erosion is the transport of soil by natural forces (mainly water and wind). 3.4.1 ● Rill erosion: rills are small furrows caused by surface runoﬀ on bare soil, often begins ● on paths used by people; ● Donga erosion: dongas or gullies form when smaller rills become deeper and wider; ● Sheet erosion: removal of thin top layer evenly over a large area, caused by strong winds or heavy rain in an area with little or no vegetation 3.4.2 Name any 1 of: soil texture, soil depth, rockiness of soil, slope QUESTION 4 4.1.1 basin irrigation 4.1.2 a) main canal; b) soil wall 4.1.3 Basin irrigation: ● requires flat or gently sloping land (< 5% gradient) ● soil walls divide field into a number of basins ● starting from a main canal, water is led from basin to basin ● each basin must be flat 182 © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook

X 13 Topic XX Unit Answers to Exam Practice questions 4.1.4 ● Name any 1 advantage: no power needed, no expensive equipment needed, even spread of water ● Name any 1 disadvantage: requires a lot of water, diﬃcult to control delivery of water, diﬃcult to set up and manage 4.2 Name any 3 of: salinity, sodicity, toxic chemicals, turbidity, biological/chemical pollutants 4.3.1 Crop rotation ● growing diﬀerent crops in sequence in the same field over a number of years ● sub-divides field (into 4) and plant diﬀerent family of crops on each piece of land ● swap crop families and land sections every year ● after four years, same crop is grown on original patch 4.3.2 monoculture 4.3.3 profitability, pest management, soil moisture and fertility, residue management, crop choice 4.4 Aims of soil cultivation ● killing and removal of weeds ● mixing in of organic matter and fertiliser ● burying or mixing crop residue 4.5.1 Reasons why a greenhouse is preferred: ● crops protected from natural elements and large pests ● crops can be cultivated out of season due to temperature control 4.5.2 Covers of a greenhouse: ● made of cheap polyethylene (PE) or polyvinyl chloride (PVC) materials ● materials have light transmission properties comparable to glass ● PE is UV protected, PVC will last up to five years ● can be used with light and cheap frames 4.6 Hydroponics is a method of growing plants in tightly controlled greenhouses in a medium without soil. 4.6.1 open / run-to-waste hydroponics, closed / continuous flow hydroponics © Via Afrika Publishers » Agricultural Science 11 Study Guide eBook 183

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