SOIL BIODEGRADATION OF IMAZAMETHABENZ-METHYL AND ITS ACID METABOLITE IN WHEAT CROPS AND IN SUGAR-BEET REPLACEMENT CROPS

The effect of three organic fertilizers, green manure, pig slurry, and cow manure on the rate of soil degradation of imazamethabenz-methyl u nder field conditions was investigated in a wheat (Triticum aestivum) crop sown in November. The herbicide was applied in March, 5 months af ter incorporation into the soil of the fertilizers. The half-life of i mazamethabenz-methyl in the soil was 35 days in control plots, and 55, 66 and 85 days respectively in plots treated with green manure, pig s lurry, and cow manure. In the same plots the half-lives of the sum of imazamethabenz-methyl and its herbicide acid metabolite were 61, 98, 1 27 and 172 days, respectively. The organic fertilizers thus increased the soil persistence of imazamethabenz-methyl and its acid metabolite, i.e. the product generated by hydrolysis of the methyl ester function of imazamethabenz-methyl. Towards the end of the cropping period, res idues of bath compounds became low in both fertilizer-treated and cont rol plots. Soil degradation of imazamethabenz-methyl was also studied in sugar beet (Beta vulgaris) replacement crops sown in April into lan d treated in November of the preceding year (as could occur with a tre ated winter wheat crop which subsequently failed). The rate of degrada tion in the sugar beet replacement crop was about half that of the sam e treatment applied in spring wheat.