Relationship between soil microbial biomass and gross N mineralisation

The gross rate of N mineralisation was measured under held conditions over 12 mo using the N-15 pool dilution technique. Significant differences in the mineralisation rate were found during the year, with an average rate of 610 ng N g(-1) soil d(-1). Changes in the gross mineralisation rate were not reflected in the size of the soil microbial N pool, which remained essentially stable over 12 mo. Attempts to determine the contribution of microbial N to gross mineralisation using N-15 isotope methods proved unsuccessful as we could not uniformly label the microbial N pool with N-15 in the field. The data suggested that only a fraction of the microbial biomass was involved in N mineralisation; Soil moisture and temperature were the most important factors influencing the gross rate of mineralisation. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.