RELATIONSHIP BETWEEN SOIL MICROBIAL BIOMASS AND GROSS N MINERALIZATION

The gross rate of N mineralisation was measured under held conditions over 12 mo using the N-15 pool dilution technique. Significant differe nces in the mineralisation rate were found during the year, with an av erage rate of 610 ng N g(-1) soil d(-1). Changes in the gross minerali sation rate were not reflected in the size of the soil microbial N poo l, which remained essentially stable over 12 mo. Attempts to determine the contribution of microbial N to gross mineralisation using N-15 is otope 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 influenc ing the gross rate of mineralisation. (C) 1997 Published by Elsevier S cience Ltd. All rights reserved.