Organic Colloids – Soil Organic Matter
Soil organic matter (SOM) comprises an accumulation of
i) Partially disintegrated and decomposed plant and animal residues
ii) Other organic compounds synthesized by the soil microbes upon decay.
OM content of a well drained mineral soil is LOW: 1 – 6 % by weight in the top soil and even less in the subsoil.
Sources of Soil Organic Matter
The primary sources of SOM are plant tissues
The tops and roots of trees
Shrubs, grasses, remains of harvested crops and Soil organisms
Animals are secondary sources of Organic Matter.
Waste products of animals
Remains of animals after completion of life cycle.