FIELD-SCALE MOBILITY AND PERSISTENCE OF COMMERCIAL AND STARCH-ENCAPSULATED ATRAZINE AND ALACHLOR

Recent laboratory studies have shown that starch-encapsulation (SE) ma y reduce leachate losses of certain pesticides. This study compares fi eld-scale mobility and persistence of SE-atrazine [2-chloro-4-ethylami no- 6-isopropylamino-s-triazine] and alachlor o-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 rece ived SE-formulated atrazine and alachlor, while the others received CF -atrazine and alachlor. Chemical movement and persistence was determin ed by analysis of surface samples (approximate to 3 cm) taken immediat ely after application and 1.1-m soil cores collected seven times over 2 yr. No significant difference in herbicide residue levels was observ ed between NT and CT, but there was a herbicide formulation effect. So il residue analysis suggests that SE-atrazine was more persistent and less mobile than CF-atrazine. Starch-encapsulated-alachlor was slightl y more persistent than CF-alachlor, but no differences in mobility bet ween formulations was observed. The differential field behavior betwee n SE-herbicides is attributed to the faster release of alachlor from t he starch granules. Increased atrazine persistence was attributed to t he reduction of leachate losses. The reduction in atrazine leaching is likely due to the slow release from the starch granules and subsequen t diffusion into the soil matrix where it is less subject to preferent ial how processes.