EFFECTS OF RECENT ORGANIC FERTILIZER TREATMENT ON HERBICIDE DIFLUFENICAN SOIL METABOLISM IN WINTER-WHEAT CROPS

The soil dissipation and metabolism of the herbicide diflufenican was studied in a field trial in Belgium in winter wheat which, before sowi ng, had been treated with green manure, cow manure, or pig slurry. Whe at was sown and the soil was treated with 250 g diflufenican ha(-1) in October. Diflufenican dissipated with first-order kinetics over the f irst six months with half-lives of 101, 116, 215 and 176 days in contr ol plots, green manure, pig slurry and cow manure treated plots, respe ctively. The organic fertilizers soil treatments thus increased the di flufenican soil persistence, and probably also its herbicide efficienc y. The organic amendments also decreased the soil concentrations of th e sum of the diflufenican herbicide 2 -[3-(trifluoromelhyl)phenoxy]-3- pyridinecarboxylic acid) and 3 4-difluorophenyl)-2-hydroxy-3-pyridinec arboxamide) and non herbicide 4 (2-hydroxy-3-carbbxypyridine) metaboli tes. As the organic fertilizers were applied just before sowing, their effects onto the diflufenican soil metabolism corresponded to the one s of the young soil organic matter. After 6 months, the organic fertil izers effect was less pronounced leading to diflufenican (1) and its m etabolites soil concentrations in all treatments becoming similarly lo w. The diflufenican (1) and its herbicide metabolites soil residues re maining after harvest in all the organic fertilizers treated or untrea ted plots would be too low to be harmful to a rotational crop.