COMPARISON OF MICROBIOLOGICAL METHODS FOR EVALUATING QUALITY AND FERTILITY OF SOIL

Routine soil testing procedures that are rapid and accurate are needed to evaluate C and N mineralization in agricultural soils in order to determine soil quality and fertility. Laboratory methods were compared for their usefulness in determining soil microbial biomass and potent ial activity in a Weswood silty clay loam (fine, mixed, thermic Fluven tic Ustochrept) subjected to longterm tillage, crop sequence, and N-fe rtilizer management practices. The methods included basal soil respira tion, net N mineralization during a 10-day incubation, soil microbial biomass C with the chloroform fumigation - incubation technique with a nd without subtracting a control value, soil microbial biomass N with the chloroform fumigation-incubation technique, substrate-induced resp iration, and arginine ammonification. All methods were highly correlat ed with each other and, therefore, appear to adequately reflect soil m icrobial biomass and potential activity under laboratory conditions. T he longer incubation times used with the basal soil respiration, N min eralization, and microbial biomass C and N assays resulted in higher c orrelations and lower variation among replications compared to the sho rter incubation times used with substrate-induced respiration and argi nine ammonification. The relatively rapid procedural time (3 h) requir ed for the latter two assays could make these methods more attractive for routine soil testing, although multiple assays on the same sample may be necessary because these methods are less precise than the incub ation methods that require 10 days.