E7+Soil

=__E7 Soil__=

__E7.1 What is soil?__ Soil is a combination of rock particles, air, water, living organisms and the decaying remains of dead plants and animals.

__E7.2 Soil degradation__ Acid soils, contamination, erosion, dry soil, sea water, logging, nearby industry can affect the soil quality. When soil quality has been reduced, crop production is therefore reduced, this is known as soil degradation

__E7.3 Salinization__ Salinization occurs when there is excess irrigation. Evaporation takes place in soil, leaving the salt behind.
 * The build up of salt will not allow the plant roots to take up water
 * Levels of salt build up of is toxic to plants

__E7.4 Nutrient depletion__ As plants grow, the nutrients of the soil is slowly taken out and in the end the soil is left fallow. If the nutrients are not replenished, crops will not grow as healthily. Manure added or planted with cloveer or legumes can replenish nutrients in soil.

__E7.5 Soil Pollution__ Industrial waste from tankers and used engine oil, pesticides and fertilizers can disrupt food chain and eventually affect the soil! The elements K,N,S and P is needed for soil nutrients, and also organic material

__E7.6 Soil Organic Matter (SOM)__ Decomposition of plants material produces high molecular mass molecules such as polysaccharides and proteins and smaller molecular mass molecules such as sugars and amino acid ( this is humus!)

__E7.7 Common Organic Soil Pollutants__
 * Biological || * Provides energy and nutrients ||
 * Chemical || * Cation exchange capacity - Cation are absorbed on to active sites in the humus, to prevent cations being washed away. (if toxic ions are present, it prevents these ions escaping into the ecosystem)
 * Humus helps maintain constant pH acting as a buffer ||
 * Physical || * Helps retain moisture
 * Encourages good soil formation
 * Keeps soil warm in spring as the humus turns into a dark colour to absorb heat ||
 * Hydrocarbons and VOCS, SVOCS from transport and solvents
 * Agrichemicals from pesticides, fungicides and herbicides
 * Polyaromatic hydrocarbons from incomplete combustion of fossil fuels
 * PCB's Polychlorinated biphenyls from fridges and capacitors/transformers
 * Organotin compounds found in bactericides and fungicides