ABSTRACT
This chapter discusses microbial biomass, its measurement and activity in relationship to nitrogen (N) cycling. It also presents examples that suggest a significant portion of plant available N comes from the turnover of the soil microbial biomass (SMB). SMB plays a major role as a catalyst in the decomposition of soil organic matter (SOM) and the release of inorganic nutrients in to the bulk soil where they become available for plant uptake. The microbial biomass is the driving force behind SOM transformations and nutrient cycling in soil systems. Through the metabolism of complex SOM substrates the biomass contributes significantly to plant nutrition and ecosystem functioning. There are several future research needs and questions concerning SMB and the N cycle that warrant listing. Develop a chemical measurement of active soil N. Is it possible to increase the active soil N fraction? Elucidate the relationship between SMB and the active N pool. How does global change affect SMB N cycling?.
