Introduction to soil, its components and impact of human activity

1. SOIL
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2. Composition of soil
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3. Soil degradation: Salinization
• Accumulation of water
soluble salts due to overirrigation 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
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4. 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

5. 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

6. 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
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7. 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

8. 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

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

10. 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

11. Common pollutants
Common 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