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Effect of Formulation and Tillage Practice on Volatilization of Atrazine and Alachlor

USDA-ARS, Hydrology Lab., Natural Resources Institute, Beltsville, MD 20705.

^* Corresponding author.

ABSTRACT

Conservation tillage practices are being implemented by many farmers to conserve water and soil resources. These practices may modify the soil surface in ways that differentially effect dissipation of pesticide when compared to conventionally tilled fields. We measured volatilization of atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and alachlor [2-chloro-2'-6'-diethyl-n-(methoxymethyl) acetanilide] applied as either an experimental starch-encapsulated formulation or as a commercial formulation, containing atrazine as a wettable powder and microencapsulated alachlor, to adjacent no-till and conventionally tilled corn fields in Maryland. Both formulations were applied at the same rate; 1.7 kg ha^–1 for atrazine and 2.8 kg ha^–1 for alachlor. After 35 d, cumulative volatilization of alachlor from conventionally tilled fields was 14% of that applied for both formulations. Cumulative volatilization of alachlor was less from no-till fields with 9% of the commercial formulation and 4% of the starch-encapsulated formulation being lost. After 35 d, cumulative volatilization of the commercial formulation of atrazine from the conventionally tilled field was 9% of that applied compared with 4% of that applied to the no-till field. Starch encapsulation reduced volatilization losses of atrazine to <2% of that applied for both tillage practices. Starch encapsulation appears to be a viable formulation modification for reducing volatilization losses of herbicides, especially from no-till fields.