Dissipation and mobility of flumetsulam in the soil of corn crops.

The triazolopyrimidine sulfonanilide herbicide flumetsulam has been applied pre- or post-emergence at the rate of 20 g a.i. ha-1 on corn crops grown on sandy-loam or loamy-sand soils. A procedure has been developed for the analysis of flumetsulam in soil using gas-chromatography and gas-chromatography combined with mass spectrometry, after methylation of flumetsulam and purification of the soil extracts by repeated thin-layer chromatographies. The dissipation of flumetsulam in the 0-8 cm surface soil layer followed a first order kinetics. The flumetsulam soil half-life was about 41 days for the crops grown on sandy-loam soil, and 30 days for the crop grown on loamy-sand soil. At the corn harvest in September, only 9 to 13% of the applied dose of flumetsulam remained in soil, what is a common value for the herbicides at the crop harvest. The heavy rains and the soft temperatures of the autumn should dissipate these low residues within the one or two months period after the harvest. When applied at the rate of 20 g a.i. ha-1, the persistence of flumetsulam in field soil thus was moderate. During the crops and until the harvest, in the 8-15 cm surface soil layer, low concentrations of flumetsulam at the limit of the analytical sensitivity (0.3 microgram flumetsulam kg-1 dry soil) were observed temporarily; in the 15-20 cm surface soil layer, flumetsulam was never detected, showing that flumetsulam was strongly adsorbed onto the soil and its organic matter.