Studies on the fate of chlorpyrifos in three soil types under Sudan Gezira conditions [Sudan]
1997
Osman, N.S. (University of Khartoum. Faculty of Agriculture, Shambat (Sudan))
The objective of this study was to determine the fate of the insecticide chlorpyrifos in soil under the Gezira conditions. It was tested in three types of soil: sand silt loam. and clay soil under laboratory, outdoor conditions and the field for plant residue evaluation. It was found that, under laboratory conditions, rapid disappearance of chlorpyrifos occurred during the first four weeks, followed by a slower rate of loss. The half-lives were 18.6,21 and 16.6 days for sand, silt loam and clay soil respectively. Under outdoor conditions rapid disappearance was observed in non-sterilized and cultivated soils, which is likely due to microbial activity. Loss in sterile soil was relatively slow. It was found that the average half-lives in the treatments were 4.9 days for sand 5.3 days for clay and 5.9 days for the silt loam soil.In comparison with the laboratory experiments, which showed and average half-life ranging from 2.5 to 3 weeks in the three soil types, the effect of outdoor conditions in speeding up the loss of chlorpyrifos is well demonstrated. Under field conditions traces of chlorpyrifos residues were found in onion three months after treatment. The levels were less than the maximum residue limit for onions (MRL) (0.05ppm). No residues could be detected at harvesting time. Thus, on bases of these findings chlorpyrifos is unlikely to present a significant carry over problem from one growing season to the next when used in these soil types at the recommended rates
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