A quantitative study of asulam persistence in soil

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Abstract
The persistence of the herbicide asulam was studied at different controlled temperature and moisture levels in Regina heavy clay. Degradation was rapid, approximating to first‐order kinetics with a half‐life of about 7 days, at temperatures in the range 20–35° and at moistures of above 50% of field capacity. At lower soil temperature and/or moisture regimes, breakdown was slower. The laboratory data were used in conjunction with the appropriate meteorological records in a computer program to simulate the degradation pattern for asulam in six separate microplot field studies carried out during May to November 1976. In three of the six experiments there was close correspondence between observed and predicted residue levels, but in the other three experiments, the model underestimated rates of loss.