DYNAMICS OF SOIL MICROBIAL BIOMASS AND ACTIVITY IN CONVENTIONAL AND ORGANIC FARMING SYSTEMS

Dynamics of microbial communities during two growing seasons were comp ared in soils under tomatoes managed by conventional (2- and 4-y rotat ions), low input, or organic practices. Fumigation extractable carbon (FEC) and nitrogen (FEN), potentially mineralizable N, arginine ammoni fication and substrate induced respiration (SIR) were significantly hi gher in organic and low input than conventional systems on most sample dates. Microbial variables were significantly negatively correlated w ith amounts of soil mineral N in the conventional 4y system, whereas t hey were positively correlated with mineral N in the organic system. T he C-to-N ratios of material released after fumigation extraction were significantly higher in the conventional than organic soils. In all f arming systems, soil moisture was positively correlated with FEC or FE N, but negatively correlated with the C-to-N ratio of the microbial bi omass and SIR. Soil temperature was negatively correlated with FEC and FEN, but positively correlated with the C-to-N ratio of microbial bio mass. (C) 1998 Elsevier Science Ltd. All rights reserved.