Adsorption, decomposition and movement of oxamyl in soil

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Abstract
A study was conducted of the behaviour of oxamyl in Israeli soils of varying clay and organic matter contents. The adsorption isotherms for oxamyl were linear, and the adsorption coefficient (Kd) could be correlated to the clay content of the soils, as well as to the organic matter content of the soil. Oxamyl adsorption was underestimated by using published correlations between the adsorption and the chemical properties of pesticides, such as their solubility or octan‐1‐ol‐water partition coefficient. The decomposition of oxamyl in soils followed first‐order kinetics. The half‐life ranged from 4 to 33 days in a Bet Dagan soil. The reaction rate increased with increasing moisture content of the soil until field capacity was reached, at which point it levelled off. The Arrhenius relationship was followed, with degradation proceeding more rapidly at higher temperatures. In several soils of varying composition, which were kept at field capacity, no difference in the degradation rates was observed. Oxamyl was applied to a Bet Dagan soil from a point source in a single pulse, as a split application, and on a continuous basis. The distribution patterns of oxamyl under the various treatments differed significantly. After the single‐pulse application, oxamyl was leached out of the emitter zone. While the split application decreased the oxamyl‐free zone, the best results were obtained by continuous application, which gave a nearly uniform distribution of oxamyl in the soil.