EFFECTS OF ORGANIC FERTILIZERS ON ALDICARB SOIL BIODEGRADATION IN SUGAR-BEET CROPS

In the present work, the influences of several organic fertilizer treatment regimens were compared as to their slowing down effect on aldicarb soil metabolism in a sugar beet crop. The organic fertilizers treatment schemes had been repeatedly applied in the past 30 years, according to a 3-year rotation cycle. The following organic fertilizers treatment regimens-which are the main ones used in the agronomy practice-were compared: Treatment 1: no organic fertilizer at all; treatment 2: 40 tons cow manure ha-1; treatment 3: 40 tons pig slurry ha-1 + green manure + crop wastes; treatment 4: green manure + crop wastes; treatment 5: straw cereal wastes alone. A sugar beet crop was sown in April 1991, 1 kg aldicarb ha-1 being applied in granulates in the sowing furrow. During the 2.9 first crop months, the soil half-lives of the sum of the insecticide S-+SO-+SO2-aldicarb in the sowing line in the 0-25 cm surface soil layer were 21.6, 44.4, 39.6, 35.7, and 30.3 days in the treatments 1, 2, 3, 4, and 5 treated plots, respectively. The organic fertilizers soil treatments thus increased the persistence of the total insecticide compounds soil concentrations, and probably also the insecticide protection efficiencies. Comparison of the results obtained here with the ones previously obtained with other crop trials, herbicides and soil insecticides, suggests that the soil organic matter is the most efficient to slow down the insecticides soil biodegradation, compared to the old humus originating from the organic fertilizers treatments made more than one year ago. After the three first sugar beet crop months, the effect of the organic fertilizers treatments on the aldicarb and its insecticide metabolites soil persistences disappeared, their soil concentrations become very low and similar in the organic fertilizers treated and untreated control plots.