What is soil organic matter (SOM) primarily composed of?

Soil organic matter (SOM) is primarily composed of a complex mix of materials that includes decomposed plant and animal residues, microbial biomass, and organic compounds such as humus. This complexity is essential because it contributes to various soil properties, such as nutrient supply, moisture retention, and soil structure. The diversity of materials in SOM indicates that it serves multiple functions in the soil ecosystem, enhancing fertility and fostering a healthy environment for soil organisms.

Other options, such as a single nutrient source or only decomposed plant material, fail to recognize the multifaceted nature of SOM. While decomposed plant material is a crucial component, SOM also includes animal residues and microbial products, highlighting the importance of biological activity in soil health. The idea that SOM is purely mineral composition is incorrect, as it ignores the organic components that play a vital role in soil function and sustainability.