Effects of recent organic fertilizer treatment on herbicide diflufenican soil metabolism in winter wheat crops

Abstract

The soil dissipation and metabolism of the herbicide diflufenican was studied in a field trial in Belgium in winter wheat which, before sowing, had been treated with green manure, cow manure, or pig slurry. Wheat was sown and the soil was treated with 250 g diflufenican ha(-1) in October. Diflufenican dissipated with first-order kinetics over the first six months with half-lives of 101, 116, 215 and 176 days in control plots, green manure, pig slurry and cow manure treated plots, respectively. The organic fertilizers soil treatments thus increased the diflufenican soil persistence, and probably also its herbicide efficiency. The organic amendments also decreased the soil concentrations of the sum of the diflufenican herbicide 2 (2-[3-(trifluoromelhyl)phenoxy]-3-pyridinecarboxylic acid) and 3 (N-(2,4-difluorophenyl)-2-hydroxy-3-pyridinecarboxamide) and non herbicide 4 (2-hydroxy-3-carbbxypyridine) metabolites. As the organic fertilizers were applied just before sowing, their effects onto the diflufenican soil metabolism corresponded to the ones of the young soil organic matter. After 6 months, the organic fertilizers effect was less pronounced leading to diflufenican (1) and its metabolites soil concentrations in all treatments becoming similarly low. The diflufenican (1) and its herbicide metabolites soil residues remaining after harvest in all the organic fertilizers treated or untreated plots would be too low to be harmful to a rotational crop.