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 activity of soil microbial biomass have been investigated, under laboratory conditions, 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 concentrations. No adverse effects on microbiological processes were observed at the field dose. Decreases in the microbial biomass-C content, ATP contents and dehydrogenase activity, and increases in the global hydrolytic capacity, catalase and nitrogenase activity, in comparison with the untreated soil control, were found at the higher dosages. The onset and magnitude of these effects were dependent on temperature and humidity conditions, however, they were generally slight and transitory. These findings are discussed in terms of rimsulfuron toxicity to the soil microbial biomass and any consequent release of endocellular enzymes from the dead micro-organisms.