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Soil organic matter (SOM) integrates many soil properties and can serve as an indicator of the soil’s health and level of various soil processes.
Soil organic carbon (SOC) is a fraction of the soil organic matter. SOM provides the carbon and energy for soil organisms and thus also supports the biological functions of soil. It affects the soil’s capacity to retain and release nutrients for plant growth by contributing to cation exchange capacity, and through mineralization of organic nitrogen, phosphorus, and sulfur. SOM also affects soil water storage and release and exchange of gases with the atmosphere by influencing soil pore size distribution and bulk density by aggregation of soil particles.
Soil organic matter can also reduce the toxicity of certain elements and chemicals through chelation. SOM and SOC content is determined by several factors, including the amount of sand, silt, and clay; the climate; and soil management. Clayey soils have higher SOM contents than sandy soils, and wetter areas have higher SOM content than drier areas.
The content is ultimately determined by the balance between the addition of organic inputs to the soil and decomposition; soil management practices can dramatically affect decomposition rates of SOM (SOC) by soil biota.