The undecomposed animal and plant residues and organisms in soil are called organic residues, which is called soil organic matter in China. One part of organisms is soil animals and crop roots, and the other part is soil microorganisms, accounting for 2% ~ 12% of total soil organic matter. In most of the current research work, microorganisms formed by humus, animal and plant residues and microorganisms are collectively called soil organic matter.

Soil organic matter in a broad sense refers to all kinds of carbonaceous organic matter in the soil, which contains nutrients needed for plant growth.

The source of forest soil organic matter is mainly litter, which belongs to acidic organic matter; Grassland soil is mainly grass and roots, belonging to neutral organic matter; Farming soil mainly includes crop residues (generally accounting for 35%~40% of seed products) and applied organic fertilizer. It is mainly composed of about 25% water and 75% dry matter.

forest

Organic matter is the source of available nutrients for crops in agricultural ecosystem, and most of nitrogen, phosphorus, sulfur and some trace elements absorbed by crops come from the mineralization of soil organic matter. Organic matter also affects the composition of aggregates, which can improve the arable, air permeability and water permeability of soil. The water absorption capacity of soil organic matter can reach dozens of times its own weight, so it has a positive effect on maintaining soil moisture.

Schematic diagram of influence of biochar on soil root system

Aggregates formed by soil mineral particles and organic matter can enhance the ability of soil to resist wind erosion and water erosion. Some water-soluble organic compounds (WSOM) will affect the application effect and retention time of pesticides in soil. Therefore, soil organic matter occupies the primary position in the composition of soil quality, and it is generally believed that the content of soil organic matter is positively correlated with soil quality.

Schematic diagram of influence of biochar on soil root system

Generally speaking, the content of soil organic matter is closely related to climate, vegetation, topography, soil types and farming measures. At present, the content of soil organic matter in China is generally low. Due to the long-term local application of chemical fertilizer to the planted natural soil, the level of soil organic matter will drop more obviously, which is easy to cause soil hardening and salinization.

Salinization performance of soil in vegetable greenhouse

Part of the contents refer to the paper "Research progress on the concept and grouping technology of soil organic matter *", which should be published in the Journal of Ecology, Volume 15, April 4, 2004.