The microbial biomass consists mostly of bacteria and fungi, which decompose crop residues and organic matter in soil. This process releases nutrients, such as nitrogen (N), into the soil that are available for plant uptake. About half the microbial biomass is located in the surface 10 cm of a soil profile and most of the nutrient release also occurs here. Generally, up to 5% of the total organic carbon and N in soil is contained in the microbial biomass at any one time. When microorganisms die, these nutrients are released in forms that can be taken up by plants.