Sources of Soil Organic Matter

Soil organic matter comes from a wide range of sources. Soil organic matter can be divided into humus and non-humus. Microorganisms are the earliest source of soil organic matter.

The following components are important sources of soil organic matter:

1) Plant residues: including apoplastic material of various plants, dead plant bodies and root systems. This is the main source of soil organic matter in its natural state. Forest soils are characterized by a large amount of apoplastic matter and a large tree root system compared to agricultural soils. The dry matter mass of apoplastic matter in tropical rain forest can reach 16700kg/(km2-a), while the dry matter mass of apoplastic matter in desert plant communities is only 530kg/(hm2-a).

 2) Animal and microbial residues: including the residues of soil animals and non-soil animals, and the residues of various microorganisms. This part of the source is relatively small. However, for virgin soils, microorganisms are the earliest source of soil organic matter.

 3) Animal excreta and secretions: Although the amount of this source of soil organic matter is small, it plays a very important role in the transformation of soil organic matter.

 4) Waste water and residues: various organic fertilizers (green manure, compost, compost, etc.) applied to the soil, industrial, agricultural and domestic waste water, waste residues, etc., as well as various microbial products, organic pesticides, etc. In traditional agricultural production, farmers collect a large amount of human and animal excrement to meet plant nutrition and maintain organic matter in cultivated land.