Chapter 3 Agriculture PDF

Chapter 3 Agriculture and the environment  3.1 Soil composition What is soil? Soil is a habitat for plants and other organisms that grow within it. It is made from a number of components. There are four main groups: *mineral particles: which are a combination of rock fragments an...

Chapter 3 Agriculture and the environment  3.1 Soil composition What is soil? Soil is a habitat for plants and other organisms that grow within it. It is made from a number of components. There are four main groups: *mineral particles: which are a combination of rock fragments and other smaller inorganic(non-living items). They are formed due to physical, chemical and biological weathering of the parent rock. *organic content, which is a mixture of living plants and animals and their dead remains. *air, which is held within the space (pores) between the particles and organic content of the soil. Air enters the soil by diffusion. *water, which is held within the soil pores and is the water that is available for plant growth. Water enters the The proportion of these components depends on: *type of soil *way it has been managed *local climatic conditions *size of minerals particles The proportion of components in a typical cultivated soil *Where do soil components come from? *The mineral particles occupy the largest volume within soil. The particles are formed from the weathering and erosion of the parent rock. *Weathering the movement of the fragments. *Erosion the movement of soil components. *The weathering of rock can take a number of forms, physical is often caused by frost, heat, water and ice or wind. Chemical can be caused by carbon dioxide combining with water to form weak acid. Biological is caused by processes such as growth of plant roots.  Particle size *The size of the soil particles has a major effect on the proportion of the soil : how well it holds or drains water, its capacity to hold mineral nutrients. *Soil mineral particles can be classified according to their size into 3 groups: -Sand -Silt -Clay Particles size The classification of soil type and their characteristics  3.2 Soil for plant growth *Soil is the cheapest and most abundant medium in which water, mineral nutrients, anchorage to hold roots and oxygen can be supplied to a plant. *Plants require: 1. a supply of mineral ions to grow well, nitrogen, phosphorous, potassium and a range of other elements to construct proteins and carry out life processes. 2.Soil pH The uptake of nutrients by roots is affected by pH of the soil, a measure of the acidity or alkalinity. In absolute terms the pH scale runs from 1 acid to 14 alkali. The pH of a soil may be dependent on a number of factors: *type of parent rock *pH of water that flows inti the area. Soil pH affects the uptakes of nutrients and the availability of nutrients. Farmers can try changing the pH of the soil either to acidify it using fertilizers that have an acid effect or make it alkaline adding ground limestone. 3.Soil organic content The organic content of the soil is a combination of living organisms and their dead remains. AS with other plants and animals, the organisms that live within soil (decomposers which make soil rich in humus) such as earthworms, fungi and bacteria. *Earthworms breakdown vegetation, mix the soil, aerate the soil, spread organic matter through the soil. * Bacteria work on organic matter, covert waste products to simple chemicals, some convert nitrogen to nitrate, important in nitrogen cycle. *Fungi feed directly on dead matter, digest hard wood items, aid plants to take up nutrients through their roots. High levels of organic matter: *increase water-holding capacity (like sponge) *increase air spaces in the soil *increase number of decomposers, tunnels and burrows in the soil, providing additional drainage and less compaction *prevent loss of mineral nutrients (humus holds on to mineral nutrients)  Sandy soil and clay soil Characteristics of sandy soils include: -free drainage (because of the large air spaces between particles). -low water-holding capacity. -quick to warm up because the spaces between particles hold less water. -easier to cultivate because particles do not stick together easily. -poor retention of nutrients because there is less opportunity for particles to bind mineral ions and more opportunity for leaching. -a greater risk of erosion because the particles do not stick together tightly. Characteristics of clay soil include: -high water-holding capacity. -slow to warm up because of the large amount of water held in spaces between the particles. -small air spaces, which are harder for roots or organisms to penetrate and contain less oxygen. -water does not drain away easily. -harder to cultivate because it sticky and wet after heavy rain, dries hard and cracks after prolonged exposure to sunlight, and is heavy because of its high water-holding capacity. -retains nutrients well(clay particles have an electric charge that binds to mineral ions.  3.3 Agriculture * There is no one definition for agriculture, agriculture is typically defined as the cultivation of animals, plants and fungi for food and other products used to sustain human life. *The type of agriculture used in different parts of the world depends on a number of factors, including: -climate -culture -technology -economics *Agriculture type: arable, pastoral and mixed subsistence and commercial  Extensive versus intensive -Farm production can also be described by evaluating the relative yield compared with the size of space used. - Extensive production occurs when there is a relatively small amount of production (either crops or animals) from a large area of land. - Intensive production occurs where large amounts are produced from small areas of land. This style of production tends to have high 'inputs', such as a lot of labour, fertilisers or machinery. -Extensive production: farming that is spread over a wide area and uses less resources per metre of land - Intensive production: farming that aims to maximise the yield from an area using a large amount of resources  3.4 Increasing agricultural yields *The demand for food keep on increasing as the global population increases. Therefore, there is pressure on food production in a number of ways, including: -an increasing world population needing more resources -climate change affecting the availability of fertile land -increasing settlement sizes reducing available farmland -increasing in the standard of living creating a demand for more food variety -larger populations impacting on the availability of water for irrigation  Techniques for improving crop yield *1-Crop rotation: the principle of growing different types of plants in different plots each year. -legumes :have different nitrogen-fixing bacteria in their root nodules. -leafy crops: vegetables that are required for their leaves (require a lot nitrogen left by legumes). -root crops: have deep root systems. -fallow : the land is ploughed but left barren for a period to restore soil fertility and to avoid surplus production. *Advantages of crop rotation: -diseases in the soil affecting the plant are left behind -pests need to find a new site, their population is reduced -the soil in the new plot is likely to have the essential nutrients Crops ready to harvest at different times, less potential waste, less labour and machinery needed. *2.Fertilisers: contain minerals such as nitrogen, potassium and phosphorus. Add on to the nutrients available in the soil. *3.Irrigation: supplying water to the crops. Importance of water: -large percentage of a plant is made up of water -essential for cell activity -used in photosynthesis -mineral nutrients uptake requires water in the soil -the water must be free from pollution and low in salt Different methods of irrigation Advantages and disadvantages of overhead irrigation Advantages and disadvantages of clay pot irrigation system Advantages and disadvantages of drip irrigation systems Advantages and disadvantages of flood irrigation *4. Insect control (insecticide and biological control), weed control (herbicide), fungi control (fungicide). -Pests: an animal that attacks or feeds upon a crop plant. -Pesticide: used to control pests. -Weed control: weed-killing chemicals are known as herbicides. -Insecticide: chemicals to kill insects. -Fungicide: a chemical used to control fungal diseases. *Weeds need to be controlled because they: -compete with crops for water, light and nutrients -reduce quality of a seed or grain crop , the weed seed affect the purity of the crop for sale -might be poisonous , either to livestock or to humans and so might result in a tainted crop -make cultivation difficult, tangling up tools and clogging up machines -can block drainage systems with excessive growth -can be a source of pests and diseases that also attacks the crop -can look untidy, which might have an impact in tourism areas *Farmers may prefer to use herbicides rather than a non-chemical control because: -herbicides are easier to manage and the weed control can be applied over a longer season -alternatives may be less effective and more variable -the use of herbicides can be cheaper -the results are more predictable, with less risk of failure -less labour is needed compared with cultural controls -the effective of herbicides can be more rapid *Alternative to herbicides are culture controls: -hand weeding and hoeing : removing individual weeds but require a lot of labour. -weeds barriers: using black plastic sheeting over the ground or a deep layer of composted organic matter helps smoother weed -flam gun : paraffin or kerosene can be used in a flam gun to scorch off the tops of weed seeds at the soil surface, suitable for use in areas before crop planted *A crop diseases is caused by fungi, bacteria or viruses(pathogens). -The most common are fungal diseases and are controlled by fungicides. -Insect control: insect-controlling chemicals are called insecticides. Alternative to insecticides biological control. *Advantages of biological control methods are: -no chemical residues are left in the crop. -there is no impact of sprays on the surrounding ecosystem. -once controlled, the population of the control agent should increase and breed, so there is no need for reapplication. -when the pest has been controlled, the lack of food will mean the predator will naturally reduce in numbers. - There is no need to water protective clothing when applying the predator. *Disadvantages of using biological control are: -the control is not as instant as chemical control -climatic conditions might mean the pest breeds faster than the predator, so the problem is not controlled -the predator might not stay on the crop and move elsewhere, instead of feeding on the intended pest -the predator might escape into the local countryside and impact the natural ecosystem and food web *6.Selective breeding The process of selective breeding is as follows: -identify which characteristics of the species are important -choose parents that exhibit these characteristics -raise the offspring from these parents -repeat the process *Examples: -dairy cattle, an increase in milk production -beef cattle, an increase in muscle size -wheat, increased disease-resistance and higher yields -rice, an increase in yield *Disadvantages of selective breeding: -it is a relatively slow process and has low success rate. -testing and evaluation can take 20 years. *5.Efficiency grains through mechanization -Using machines such as tractors means that larger areas can be cultivated easily by one person. This reduce the labour costs for the farmer and also means they are cropping from a larger areas. -Ploughed can be done even when soil is heavy. -Additional attachments can be done to apply fertilizers and pesticides. -Large machines work best in large fields because time is lost when they need to change direction. *7.Genetically modified organisms (GMO) GMO: an organism whose genetic material has been altered by genetic engineering. -A piece of DNA from one organism into the genetic code of another. *There are many different reasons for GM plant species(advantages): -disease and pest resistance: genes can be cut from a resistant plant and added to a crop plant. -nutritional value: plants can be developed that are more nourishing. -growth of plants in inhospitable areas. -higher yields. -herbicides resistance, which would allow farmers to spray the whole crop and its weeds and only affect the weeds. -less use of pesticides, if the GMO plant is pest resistant. -crops with longer storage lives, leading to less food wastage. *Disadvantages of GMOs include: -the unknown impact of the new characteristics on human health. -the products are not natural. -the genes might get into wild plants if they interbreed with GMOs. -issues for other insects caused by insect-resistant varieties. -reduction in the gene pool. *8.Controlling the crop environments( greenhouse, hydroponics): Greenhouse: use to manage the environment for plant growth, a building made of glass or similar transparent material that is used manage the environment for plant growth. *Some techniques to control the environment: -providing shade for cattle so that they do not get too hot -using windbreaks at the edges of crops to reduce wind speed and prevent damage to the crops -removing trees that shade a crop in order to maximize the light the plant receive Hydroponics *Hydroponics: growing plants without soil, with the nutrients the plant needs dissolved in water, this technique is often used in conjunction with a growing blueprint. *Advantages of hydroponics: -no need for soil -can be used anywhere (there are experiments being carried out in space) -an intensive system that can provide high yields -easy to harvest -plants are given exactly the nutrients they need in the irrigation water -water is cycled, so used efficiently -no weeds or pests and diseases in the soil -pollutants are not released into the environment *Disadvantages of hydroponics: -it is expensive to set up -only suitable for small production areas -requires a lot of technical knowledge -disease. If present, is rapidly spread through the water supply to all plants -plants can die quickly if conditions are not maintained at optimum levels  3.5 Impacts of agriculture *Impacts of agriculture: 1-Overuse of herbicides and insecticides -Regular use of one insecticide can cause resistance within pest population. Solution: use a range of different pesticides -Unintended environmental damage: beneficial insects like bees are also affected and food web is disturbed. -Spray drift: herbicides stay longer in the soil and may affect the next crop. -heavy rainfall can cause leaching of the chemicals into lakes 2-Overuse of fertilizers: -addition of extra mineral nutrients is waste of money and resources if the soil has reached its maximum level -heavy rain can dissolved the nutrients and cause leaching -excess water containing dissolved fertilizers drain into nearby lakes and rivers, leading to eutrophication -nitrates from fertilizers if consumed can cause diseases such as blue-baby syndrome -large quantities can affect the pH of the soil and in turn, the availability of minerals -too much of trace elements can be toxic to the plant -too much fertilizer dehydrate the plant (scorching) -imbalance of nutrient makes the plant produce lots of foliage, but no flower *Solution: strict limits on where, when and how the fertilizers must be applied, can replace with organic fertilizers 3-Mismanagement of irrigation causing salinization and water logging *damage to soil structure, soil is compacted *death of plant roots as waterlogged soils prevent plant roots from getting enough oxygen *loss of nutrients as they are dissolved and washed away with water *high levels of run-off, soil erosion *soil capping: surface of the soil becomes hard *salinization: salt content of the soil can increase -irrigation water soaks into the soil to a great depth -salts dissolved in the water at great depth -water evaporates from field -water and salts are drawn up to the surface -salt remains at the surface and kills plant roots *prevents soil cultivation as it’s difficult to cultivate soil with a high- water content 4.Over-production and waste -waste from over-production: too much of a crop might mean that some will not be sold -waste of storage space: it may take longer to sell a crop, so building are needed to store the spare harvest. Some crops need special conditions so they do not spoil -waste of transportation: to sell all the crop, a farmer may need to travel larger distances, using more fuel -waste of quality produce: if a crop starts to decrease in quality because it has not been sold quickly enough, it will be worth less money -waste of labour : the farmer may have to staff to help grow and care for the crop , which is not an efficient use of time and labour if too much crop is produced 5.Exhaustion of mineral ion content -the farmers use the soil over and over again with little to no rest which leaves the soil depleted of nutrients and minerals *Solution crop rotation, mixed cropping and leaving the land fallow 6.Soil erosion -over- cultivation: soils that are cultivated regularly lose soil structure and are more vulnerable to erosion as they break down to smaller particles. 7.Cash crops replacing food crops: most commercial farmers prefer to grow crops that generate more cash. This causes a decline in the staple food available.  3.6 Causes and impacts of soil erosion Causes of soil erosion: 1-removal of natural vegetation: no more roots to bind the soil together or slow down the torrents of water, so flash flooding and rainwater run-off pick the soil and carry it away. 2-over-cultivation:ploughing breaks the soil into smaller and lighter particles. These are more easily carried away by wind. 3-over-grazing: livestock reduces the vegetation to nearly ground level, sometimes leaving no roots to hold the soil. Animals trample down the plants and their hoofs compact the ground. 4-wind erosion :deforestation(due to need for space, excessive grazing, increase in development of arable crops) increases the chance of soil getting erode by wind. 5-water erosion: heavy rainfall carries particles away. -excess run-off water that can’t be absorbed by soil transports the soil from that area -soil compaction reduces infiltration -gully erosion ( volume of water erodes local soil further) forms and deeper and deeper cervices  Impacts of soil erosion *Topsoil is removed the most productive layer is absent (subsoil is lacks in nutrients and air spaces. As result of the loss of topsoil , there is loss of habitat for many organisms in the area, impact on the entire ecosystem. *Silting up water courses: flooding occurs as water bodies can’t hold excess water (space taken up by silt). *Silt deposits can form lagoons: providing breeding ground for mosquitoes. Silt affects the quality and availability of water for drinking. *Aquatic organisms are buried under the silt layer, preventing light from reaching the underwater plants (low oxygen levels in ecosystem, no photosynthesis). *Desertification: the process by which fertile land becomes desert. Severe drought lead to migration of the whole community. Risk of famine and malnutrition, leading to less food source. * Displacement of people ,relocating to neighboring country Methods to reduce soil erosion 3.7 Managing soil erosion 3.8 Sustainable agriculture