Influence of bovine manure on dissipation of hexazinone in soil

The effects of bovine manure (BM) on the degradation of hexazinone and formation of three of its major metabolites were investigated in sandy loam soil. The degradation half-life of hexazinone was 29.6 days in unamended soil, while it decreased to 21.8 days in BM-amended soil. The major metabolites formed in unamended soil were [3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1, 3H)-dione] (metabolite A) and [3-cyclohexyl-1-methyl-1,3,5-triazine-2,4,6(1, 3, 5H)-trione] (metabolite C), while metabolite B [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1, 3H)-dione] was not detected over the entire experimental period. However, in BM-amended soil, metabolite B was detected at 20 and 40 days after incubation, suggesting that BM contributed to formation of this metabolite. N-demethylation, removal of the dimethylamino group with formation of a carbonyl group at the 6-position of the triazine ring appeared to be the principal mechanisms involved in hexazinone metabolism in unamended soil. However, hydroxylation at the 4-positon of the cyclohexyl group as well as the above two modes were the principal pathways in BM-amended soil.