Environmental Effects on Metsulfuron and Chlorsulfuron Bioactivity in Soil

Abstract Metsulfuron {2‐[[[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐71)amino] carbonyl]amino]sulfonyl]benzoic acid}, a sulfonylurea herbicide, is persistent in soil and may injure susceptible crops. To elucidate potential carryover situations, the effect of environment and soil factors on metsulfuron bioactivity was examined in a Platner loam (fine, montmorillonitic, mesic, Aricidic Paleustolls) and a Valent sand (mixed, mesic Ustic Torripsamments) soil with a corn (Zea mays L.) root bioassay. Increasing soil temperature from 8 to 24°C in the loam soil reduced the duration of metsulfuron bioactivity by 49%. The temperature effect on metsulfuron bioactivity in the sand was less pronounced, as the 16°C increase resulted in only 20% reduction of duration of bioactivity. The effect of soil water content on metsulfuron bioactivity was soil and temperature related. Increasing soil water increased metsulfuron degradation in the sand at 24°C, but not at 16°C, while in the loam, metsulfuron degradation was not affected by soil water level at either temperature. Incorporating metsulfuron in soil reduced the duration of bioactivity, while the presence of growing wheat (Triticum aestivum L.) plants in metsuifuron‐treated soil did not affect the duration of bioactivity. Metsulfuron retained on surface straw residue was washed off by simulated rainfall, but duration of metsulfuron bioactivity was increased by this straw residue retention. Chlorsulfuron {2‐chloro‐N‐[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl) amino]carbonyl]benzenesulfonamide}, another sulfonylurea herbicide, persisted slightly longer than metsulfuron at the same rate in both soils when incubated at 16°C with identical soil water levels.