Mineralization of metsulfuron-methyl in Chinese paddy soils

A laboratory study was conducted to investigate the mineralization of metsulfuron-methyl (MSM) in paddy soils in response to soil moisture, temperature and soil properties. The results indicated that MSM mineralization was relatively limited in the paddy soils when soil temperature was low. Only 2.2–6.0% of the applied 14C mineralized after 84 d of incubation at 15 °C. The mineralization of MSM was enhanced by increasing soil moisture and soil temperature. Soil moisture would have different impact on the response of MSM mineralization to variation in soil temperature. An increase of 10 °C accelerated the average rate of MSM mineralization by 2.3 times at 50% water-holding capacity (WHC) and 1.9 times at 40% WHC. Regression analysis showed that soil pH, organic carbon contents, microbial biomass carbon contents, and silt/clay fractions were the dominant factors affecting MSM mineralization, with pH as the most important factor. The relatively slow mineralization rate of MSM suggested long persistence of this herbicide in soil, thus increasing its potential ecological risk, especially when applied in alkaline soils and in cold areas.