SOIL MICROBIAL BIOMASS ESTIMATED BY FUMIGATION EXTRACTION AND SUBSTRATE-INDUCED RESPIRATION IN 2 PESTICIDE-TREATED SOILS

An incubation experiment was performed with two soils and five pestici de treatments (benomyl, isoproturon, simazine, dinoterb and chloroform ). Microbial biomass C and N was estimated by fumigation-extraction (F E). Two modifications of the substrate-induced respiration (SIR) metho d were used: (1) a continuous flushing system and (2) a static system with soil slurry. In addition, CO2 production was measured. Estimates of biomass C by the two SIR methods were generally higher than those o btained by the FE method. The two SIR measurements and the two biomass estimates were closely correlated, indicating a similar response to p esticide treatments. Pesticide application almost always reduced the s ize of the microbial biomass. Of the different ways of measuring bioma ss, the FE method revealed the largest number of significant differenc es from the nil treatment. The biomass C-to-N ratio was only slightly influenced by soil or pesticide treatments. Apart from the benomyl tre atment, pesticide application always increased soil respiration during the 0-10 day incubation.