Etudes des correlations entre biomasse microbienne et differentes fractions d'azote organique presentes dans deux sols lorrains

Soil microbial biomass C was measured by a fumigation-incubation method during a 2 yr period in a leached brown soil and a pelosol, two soil types developed under a semi-continental climate. To assess the influence of soil management, the soils were sampled in cultivated (maize monoculture) and uncultivated close areas (oak forest). At the same time, chemical fractionation of soil organic nitrogen, as acid-hydrolyzable distillable-N, acid-hydrolyzable non-distillable N (NSAnD) and non-hydrolyzable N was performed. Both microbial biomass C and NSAnD (mainly amino-acid N) exhibited spring and autumn maxima. Soil microbial biomass C. expressed as percent of total organic C, or biomass N (biomass-N = biomass-C: 8) as a percentage of total N. and NSAnD were found to be correlated, with a higher coefficient in leached brown soil than in pelosol. NSAnD content of soils was increasing under cultivation. Biomass N percent of NSAnD almost constantly remained at a higher level under forest than under cultivation (13 and 10% for leached brown soil, 20 and 15% in the clay-rich pelosol, respectively) corresponding to biomass-C/N ratio > 8 in forest soils. Then, an easy chemical method for assessing microbial biomass C (not biomass N) in a given soil could be NSAnD measurement after calibration through the benchmark fumigation-incubation method.