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SOIL

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Composition of soil

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Soil degradation: Salinization•Accumulation of water soluble salts due to over-irrigation or rise in water table due to removal of native plants• Irrigation water contains – CaCl2, MgSO4, NaCl

•Water evaporates, salts not washed away due to poor drainage

•Salts accumulate in the topsoil and prevents plants from taking up water

Nutrient depletion•Removal of essential nutrients and minerals from the soil food web by overuse of soil•Decrease in soil quality•Decrease in crop yield•Effects food supply•Can be remedied with fertilizer•Overuse of nitrate and phosphate can pollute ground and surface water – leads to eutrophication

Soil pollution or contamination•Agricultural•Arises from presence of man-made chemicals e.g. pesticides and herbicides•Pesticides – target insects•Herbicides – target plants (weeds) and fungi• Inorganic fertilisers – build up of nitrates and phosphates•Domestic• Land-fills• Industrial

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Soil organic matter (SOM)• mixture of non-living organic matter in the soils at various stages of decomposition•Amount of C present is a measure of amount of organic matter present

Relevance of SOM• Improves soil quality•Contains a pool of minerals for plants•Good water holding capacity• Improves soil structure•Reduces soil erosion•Functions of SOM is physiological, biological and chemical

Biological action of SOM•Binds to nutrients and is a reservoir for N, P and S•Nitrogen• Synthesis of proteins and chlorophyll

•Phosphorus• Synthesis of enzymes and storage of energy

•Sulfur• Synthesis of amino acids

•Bacteria and fungi decompose SOM and make nutrients available to plants

Minerilization•Slow process by which N and P is released to plant roots

Physical functions of SOM•Soil clusters together•Reduces soils erosion and increases diffusion of water and air through soil•Acts as a sponge and retains water better• Improves soil structure – easier for plant roots to travel through•Affect thermal properties – higher water quantity means smaller temperature changes in soil

Common pollutantsCommon pollutant Source

Petroleum hydrocarbons Petroleum industry

Agrichemicals Pesticides, herbicide, fertilizers

VOCs Household products, gasoline, glues, paints, chemicals for copiers and printers

Solvents Dry cleaning, electronics industry, manufacture of paints

Polyaromatics carbons Tar, coal, crude oil spills, wood fires, industrial waste, incinerator waste

Organotin compounds PVCs, ship paints

Polychlorinated biphenyls (PCBs) Incinerator stacks, leaks from enclosed electrical equipment, hydraulic fluid leaks

SVOCs Pesticides, herbicides, preservation chemicals