The definition of the soil microbial biomass is the living portion of the soil organic matter,
excluding plant roots and soil animals larger than 5 x 10-3 um3
. The microbial biomass generally
comprises approximately 2% of the total organic matter in soil and it may be easily dismissed as
of minor importance in the soil. However, this chapter will introduce the biomass as an important
agent in controlling the overall biological activity of the soil.