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Field-Scale Mobility and Persistence of Commercial and Starch-Encapsulated Atrazine and Alachlor

USDA-ARS Hydrology Lab., Natural Resources Inst., Beltsville, MD 20705;
Agricultural Engineering Dep., Univ. Maryland, College Park, MD 20705.

^* Corresponding author.

ABSTRACT

Recent laboratory studies have shown that starch-encapsulation (SE) may reduce leachate losses of certain pesticides. This study compares field-scale mobility and persistence of SE-atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and alachlor [2-chloro-N(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] to that of a commercial formulation (CF) of atrazine and alachlor. The research site consisted of four (0.25 ha) fields. Two fields were under no-tillage management (NT) and two were under conventional tillage (CT). One field in each tillage system received SE-formulated atrazine and alachlor, while the others received CF-atrazine and alachlor. Chemical movement and persistence was determined by analysis of surface samples (3 cm) taken immediately after application and 1.1-m soil cores collected seven times over 2 yr. No significant difference in herbicide residue levels was observed between NT and CT, but there was a herbicide formulation effect. Soil residue analysis suggests that SE-atrazine was more persistent and less mobile than CF-atrazine. Starch-encapsulated-alachlor was slightly more persistent than CF-alachlor, but no differences in mobility between formulations was observed. The differential field behavior between SE-herbicides is attributed to the faster release of alachlor from the starch granules. Increased atrazine persistence was attributed to the reduction of leachate losses. The reduction in atrazine leaching is likely due to the slow release from the starch granules and subsequent diffusion into the soil matrix where it is less subject to preferential flow processes.

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