dry farming techniques ► Dry farming techniques include any technique which conserves water or prevents the evaporation of too much water from the soil surface in the dry season. These techniques include minimum tillage, mulching, use of manure and compost and cover crops. Controlled irrigation (using manual systems, hoses or sprinklers) may be used to water crop plants in the dry season.
Practical activities:
1. Use an A-frame to establish
contour lines. See page 346 for • Soil consists of four components: mineral matter, organic matter, water and air. advice on using an A-frame. • The mineral component is derived from rocks by physical, chemical and
2. Visit a watershed management biological weathering.
area. • Most physical weathering is brought about by frost, but stresses from roots, the
action of water, wind and the sun can contribute to breakdown of rocks. • Chemical weathering alters the chemical nature of rock and can be brought
about by water, oxygen and carbonic acid.
• Biological weathering refers to the activities of living organisms which bring about the disintegration of rocks and the formation of soil.
• Volcanic soils are formed from the magma and volcanic ash which follow an eruption.
• Plant and animal matter is broken down by soil micro-organisms to form humus.
• Some animals contribute to soil formation by burrowing, and plant roots create channels in the soil.
• Farming activities such as land clearing, mining and tillage affect soil formation and fertility.
• A soil profile refers to the vertical wall of a pit showing different horizontal layers or soil horizons, each with varying physical and chemical properties. • The mineral component of soil consists of different sized particles classified as
gravel, sand, silt and clay.
• The organic matter is made up of the dead and decaying remains of plants and animals in the process of being broken down to form humus.
• The soil water, containing dissolved mineral salts, is present in the pore spaces and as films around the tiny mineral particles.
( It • • tg • 11 • [11 • to • • :al • as • • :es
• Soil air depends on the air-water relationship in the pore spaces. It is important for aeration, root respiration and biochemical processes.
• Soils may be classified into sand, clay and loams, depending on the proportions of the different sizes of the mineral particles.
• Soil texture is dependent on the size and relative proportions of the different mineral particles.
• Soil structure is dependent on the aggregation of the mineral particles into lumps and crumbs.
• Soil porosity and soil aeration are interdependent and are affected by the drainage of the soil.
• Soil temperature affects living organisms in the soil, particularly the activities of the micro-organisms. Mulching, vegetation cover and irrigation can help to keep soils cool.
• Soil contains 14 of the 17 essential mineral elements for plant growth.
• Soil nutrients are present in the soil solution and also held around the colloidal clay and humus particles.
• Soil microbes are essential for the decomposition of organic matter, the formation of humus and the recycling of mineral elements in the soil.
• The carbon and nitrogen cycles show the transformations which these elements undergo as they are cycled in nature.
• Soil fertility is influenced by climatic, biotic and topographic factors, together with the nature of the parent material and fertilisers.
• Minor elements (trace elements) are important for the healthy growth of crops. These are only required in tiny amounts but have significant effects on crop production if lacking.
• Inorganic fertilisers supply one or more of the three major nutrients, nitrogen, phosphorus or potassium, and are graded according to the proportions of each nutrient they contain.
• Soil fertility is maintained by the application of soil amendments, the use of different cropping systems, efficient soil and land management, irrigation and drainage.
• Soil amendments include fertilisers, manures, organic matter and liming materials.
• A farmer needs to work out which amendments are needed for the land and any crops grown on it.
Liming materials reduce soil acidity, increase calcium and magnesium and promote the activities of soil organisms.
Cropping systems and cultural practices help to maintain soil fertility.
Compost is made from waste plant material, such as leaves, soft stems, vegetable peelings and rejected fruits.
A compost heap can be constructed using layers of pen manure, vegetable waste, fertiliser and limestone.
Soil erosion is the process by which soil particles are carried from one area by water or wind and deposited in another area.
Natural soil erosion occurs in a natural undisturbed environment but accelerated soil erosion is caused by humans.
Soil erosion is caused by intensive rainfall which results in water running down slopes carrying soil particles with it.
Wind can cause erosion in dry or semi-arid conditions where the soil particles are loose.
Soil conservation involves retaining a cover of vegetation, planting forests, contour-cropping, strip cropping, the formation of terraces and wind-breaks. Water conservation measures include the use of storage tanks, building of pond and pools and digging of wells.
Section B: Crop Production
1101 Weathering is the breaking down of bedrock into smaller and smaller particles by physical, chemical and biological processes.
1102 Physical, chemical and biological.
ITQ3 Physical weathering is brought about by the action of frost, water and wind.
1104 Rainwater dissolves the carbonates in the rock, which then breaks up into smaller fragments.
1105 Plant roots growing in cracks exert pressure which causes rocks to split. 1106 Volcanic activity, decaying organic matter, soil organisms and human
activities.
1107 Draw a diagram with all the horizons labelled and check with the diagram on page 95.
1108 Depending on the thickness of each horizon, 0 will always be disturbed and parts of A. If the A horizon is thin, then all of A and part of B will be disturbed.
1109 Stones, sand, silt and clay; sand may be divided into fine sand and coarse sand.
11010 Organic matter is composed of the fresh and decaying remains of plant and animal material and humus.
11011 Soil air and soil water occupy the pore space in the soil. If there is a high proportion of soil air, there will be less soil water and vice versa.
11012 A loam soil has a mixture of sand, silt and clay particles in more or less equal proportions. A sandy soil has a larger proportion of sand particles. 11013 Soil texture refers to the coarseness or the fineness of the soil — the 'feel'
of the soil.
11014 The farmer can rub the soil between the thumb and fingers or the soil can be made wet and moulded in the hand.
11015 Prism-like or columnar with smooth flat faces.
11016 Climate, activities of soil organisms, presence of humus, activities of roots, tillage operations.
11017 Soil porosity is the volume of pore space in a lump of soil that is not occupied by mineral particles.
11018 Three from: soil cover; sunlight; vegetation cover; soil moisture; organic matter content.
11019 Microbial activity is increased, soil organisms are more active and the germination of seeds is more rapid.
11020 The nine macro-nutrients are nitrogen, oxygen, hydrogen, carbon, phosphorus, potassium, sulphur, calcium and magnesium. They all come from the soil apart from carbon, hydrogen and oxygen.
IT021 Nutrients are adsorbed on to clay and humus particles. They have large surface areas and surface charges which attract the nutrient ions and water.
ITQ22 It is a measure of the hydrogen ion concentration of the soil water and indicates the acidity or alkalinity of the soil.
ITQ23 The mineral salts are more soluble and more easily leached away in the rainwater.
11024 Respiration and photosynthesis. 11025 Actinomycetes, bacteria and fungi.
11026 Nitrifying bacteria convert ammonium compounds to nitrites and nitrites to nitrates.
ITQ27 Rhizobium, Azotobacter and Clostridium.
ITQ28 Climatic factors affecting soil fertility are rainfall, temperature, wind and humidity.
11029 Soils on the slopes of mountains and hills are shallow due to erosion. Fertile soils are found in the valleys. The mountainous and hilly regions are difficult to cultivate.
ITQ30 Topsoil and water in the soil are conserved. There is less erosion and the activities of soil organisms are promoted by the organic matter in the form of leaf litter on the soil.
II-031 Iron is needed for the formation of chlorophyll molecules.
11032
There is a deficiency of zinc in the soil.11033
The labels indicate the nutrient content and the nutrient ratio. 111134It
is the ratio of N, P and K in the fertiliser.ITQ35 Soil amendments are materials that supply ingredients and nutrient elements which improve soil fertility. Their function is to improve soil structure, increase water-holding capacity and ensure drainage and aeration.
ITQ36 Type of soil, crop group, crop stage and weather conditions.
ITQ37 Reduces soil acidity, increases calcium and magnesium and promotes the activities of soil micro-organisms.
11038 List to include: bottles, plastic containers, tin cans, stones, woody stems, nut grass and weed plants with seeds.
ITQ39 Fertiliser supplies nitrogen for the micro-organisms and the limestone provides a suitable pH for the micro-organisms.
IT040 Soil erosion is the process by which mineral particles are carried away from one area by water or wind and deposited in another area. 1-1041
Natural soil erosion and accelerated soil erosion.
11042
Natural soil erosion: running water on steep slopes, landslides, strong winds and sea waves. Accelerated soil erosion: burning, overgrazing, deforestation, mining, quarrying, lack of ground cover.11043
Wind can cause soil creep, which is gradual movement of particles on a surface, and saltation of sand particles, where they become airborne in strong winds.11044 Advantages: unwanted material burnt, speedy land clearing, soil sterilised, weeds burnt, harmful animals destroyed, potash added to the soil. Disadvantages: destruction of organic matter and humus, soil organisms killed, soil water lost, soil surface becomes bare, leaching of nutrients. 11045 Four from: cover crops, contour cropping, strip cropping, planting forest
trees, grass barriers, and grassed drains.
11046
The broad banks of earth prevent water running down the slope, so soil is not washed away.Section B: Crop Production