Residual phytotoxicity and persistence of chlorimuron and metsulfuron in soils of Argentina

Studies were conducted to determine the residual phytotoxicity and persistence of several rates of chlorimuron and metsulfuron in two soils of Buenos Aires Province, Argentina, using a sunflower bioassay procedure. Chlorimuron at 0, 3.6, 7.2, 14.4, and 21.6 ng g(-1) and metsulfuron at 0, 1.15, 2.3, 4.6, and 6.9 ng g(-1) were applied to a Balcarce loam soil (7.5% organic matter content, and pH 5.9), and a San Cayetano loam soil (4.0% organic matter, and pH 6.8). The residual phytotoxicity (time to achieve 90% of relative plant height to the untreated check:R-90) for both herbicides, was greater in San Cayetano soil than in Balcarce soil, likewise R-90 of metsulfuron was longer than chlorimuron in both soils. The residual phytotoxicity and persistence of chlorimuron and metsulfuron increased in the two soils with increasing rate of application. Depending on the rate, half-fives for chlorimuron ranged from 30 to 43 days at Balcarce and from 50 to 69 days at San Cayetano. In the case of metsulfuron, the half-lives were between 38 to 51 days in Balcarce soil and from 54 to 84 days in San Cayetano soil.