Microbial activity can be determined by trapping carbon dioxide (CO2) evolved from soil as the microbial biomass actively decompose soil organic matter and fresh plant residues. Activity is dependent on many factors including soil moisture (in dry soils the microbial biomass is not active), temperature (when soil moisture is present microbial activity increases as temperature increases within the range of values experienced through the agricultural zone), organic carbon (as a food source) and pH (around neutral). Decomposition of soil organic matter is controlled by the active microbial biomass and leads to the release of nitrogen and other nutrients that can become plant available.
Management practices influence microbial activity by altering organic carbon availability, pH and other soil conditions and therefore reflect rapid changes in the biological function of soil. Although microbial activity can be influenced by management factors, these changes will only be expressed where sufficient moisture is present in the soil profile – a dry soil is not active.