PAST ORGANIC FERTILIZER TREATMENTS - INFLUENCE ON THE HERBICIDE DIFLUFENICAN SOIL METABOLISM IN WHEAT CROPS

The influence of several organic fertilizer treatment regimens, applie d at the beginning of crop rotation cycles, were compared as to their slowing down effect on the herbicide diflufenican soil metabolism in w heat crops. In a first trial made at the site ''Longs Tours'', the org anic fertilizers treatment schemes had been repeatedly applied in the past since 30 years, according to a 3 years rotation cycle. The follow ing organic fertilizers treatment regimens were compared: treatment (1 ) no organic fertilizer at all; treatment (2) cow manure; treatment (3 ) pig slurry + green manure + crop wastes; treatment (4) green manure + crop wastes; treatment (5) straw cereal wastes alone. A spring wheat crop was sown and diflufenican was applied, i.e. 1.6 years after the latest external organic fertilizers application. During the 4 first cr op months, the diflufenican soil half-lives were 59, 91, 117, 81 and 7 0 days in the treatments 1, 2, 3, 4 and 5 treated plots, respectively. During the end period of the crop, the effect of the organic fertiliz ers treatments disappeared, the diflufenican and its metabolites soil concentrations becoming very low and similar in the organic fertilizer s treated and untreated control plots. A second trial was made with wi nter wheat at the site ''Les Pompes''. The organic fertilizers regimen s however had been applied only one time 1.2 years before sowing and d iflufenican application. In this trial, the organic fertilizers treatm ents had no significant influence on diflufenican soil half-life.