SOIL METABOLISM OF THE HERBICIDE ISOXABEN IN WINTER-WHEAT CROPS

Winter wheat fields were treated wi th the herbicide isoxaben after so wing. Trials were made in 1990-1991 and 1991-1992. The main isoxaben s oil metabolite was demethoxyisoxaben opyl)isoxazol-5-yl]-2-hydroxy-6-m ethoxybenzamide), i.e., the monodemethoxylation product of isoxaben. z olone(3-(1-ethyl-1-methylpropyl)isoxazolin-5-one) was the second main isoxaben metabolite. When azole(5-amino-3-(1-ethyl-1-methylpropyl)isox azole) was detected in soil, it always was at very low concentrations. It never accumulated in soil; 4 months before winter wheat harvest, i t could not be detected in soil. Benzamides 2,6-dimethoxybenzamide and 2-hydroxy-6-methoxybenzamide and 2,6-dimethoxybenzoic acid also were detected in soil. Organic fertilizer treatments increased isoxaben soi l persistence. At the crop's end, their effects, however, progressivel y disappeared, the soil residues of isoxaben and of its metabolites be coming very low and similar in the organic fertilizer treated and untr eated plots. 5-Aminoisoxazole was not detected. This work thus indicat ed that isoxaben was soil-metabolized into nontoxic products, unable t o generate toxic ones, during the wheat crops whose soil had been trea ted or not treated with organic fertilizers.