Bacteria and fungus make up the majority of the microbial biomass, which breakdown crop wastes and organic matter in the soil. This process releases nutrients into the soil that are available for plant uptake, such as nitrogen (N). The top 10 cm of a soil profile contains around half of the microbial biomass, as well as the majority of the nutrient release. One of the biological features of soil that changes quickly in response to fertilizer-like input is microbial biomass. Microbial biomass metabolic activities regulate breakdown and practically every response in the soil N cycle. Examining microbial biomass has long been a popular method in soil microbiology, especially before DNA sequencing became available. Microbial biomass is quantified to determine how the soil microbiota responds to management, environmental change, site disturbance, and pollution.