Rimsulfuron in a silty clay loam soil: effects upon microbiological and biochemical properties under varying microcosm conditions

The effects of rimsulfuron, a sulfonylurea herbicide, on the growth and act ivity of soil microbial biomass have been investigated, under laboratory co nditions, at varying conditions of temperature and humidity in a silty clay loam soil. Rimsulfuron was incorporated at the recommended field dose for maize weed control (25 g a.i. ha(-1)) and at 10-fold and 100-fold higher co ncentrations. No adverse effects on microbiological processes were observed at the field dose. Decreases in the microbial biomass-C content, ATP conte nts and dehydrogenase activity, and increases in the global hydrolytic capa city, catalase and nitrogenase activity, in comparison with the untreated s oil control, were found at the higher dosages. The onset and magnitude of t hese effects were dependent on temperature and humidity conditions, however , they were generally slight and transitory, These findings are discussed i n terms of rimsulfuron toxicity to the soil microbial biomass and any conse quent release of endocellular enzymes from the dead micro-organisms, (C) 19 98 Elsevier Science Ltd. All rights reserved.