:The dependence of the behaviour of metsulfuron-methyl on soil pH was conÐrmed during incubations under controlled laboratory conditions with two French soils used for wheat cropping. The fate of [14C] residues from [triazine-14C]metsulfuron-methyl was studied by combining di †erent experimental conditions : soil pH (8É1 and 5É2), temperature (28 and 10¡C), soil moisture (90 and 50% of soil water holding capacity) and microbial activity (sterile and nonsterile conditions). Metsulfuron-methyl degradation was mainly inÑuenced by soil pH and temperature. The metsulfuron-methyl half-life varied from Ðve days in the acidic soil to 69 days in the alkaline soil. Under sterile conditions, the half-life increased in alkaline soil to 139 days but was not changed in the acidic soil. Metsulfuron-methyl degradation mainly resulted in the formation of the amino-triazine. In the acidic soil, degradation was characterised by rapid hydrolysis giving two speciÐc unidentiÐed metabolites, not detected during incubations in the alkaline soil. Bound residues formation and metsulfuron-methyl mineralisation were highly correlated. The extent of bound residue formation increased when soil water content decreased and was maximal [48 (^4)% of the applied metsulfuron-methyl after 98 incubation days] in the acidic soil at 50% of the water holding capacity and 28¡C. Otherwise, bound residues represented between 13 and 32% of the initial radioactivity.1998 SCI ( Pestic. Sci., 53, 311È323 (1998)

The dependence of the behaviour of metsulfuron-methyl on soil pH was conÐrmed during incubations under controlled laboratory conditions with two French soils used for wheat cropping. The fate of [14C] residues from [triazine-14C]metsulfuron-methyl was studied by combining di †erent experimental conditions : soil pH (8É1 and 5É2), temperature (28 and 10¡C), soil moisture (90 and 50% of soil water holding capacity) and microbial activity (sterile and nonsterile conditions). Metsulfuron-methyl degradation was mainly inÑuenced by soil pH and temperature. The metsulfuron-methyl half-life varied from Ðve days in the acidic soil to 69 days in the alkaline soil. Under sterile conditions, the half-life increased in alkaline soil to 139 days but was not changed in the acidic soil. Metsulfuron-methyl degradation mainly resulted in the formation of the amino-triazine. In the acidic soil, degradation was characterised by rapid hydrolysis giving two speciÐc unidentiÐed metabolites, not detected during incubations in the alkaline soil. Bound residues formation and metsulfuron-methyl mineralisation were highly correlated. The extent of bound residue formation increased when soil water content decreased and was maximal [48 (^4)% of the applied metsulfuron-methyl after 98 incubation days] in the acidic soil at 50% of the water holding capacity and 28¡C. Otherwise, bound residues represented between 13 and 32% of the initial radioactivity.1998 SCI ( Pestic. Sci., 53, 311È323 (1998)