EFFECT OF STARCH ENCAPSULATION AND TEMPERATURE ON VOLATILIZATION OF ATRAZINE AND ALACHLOR

Volatilization of agricultural chemicals is one process whereby chemicals may enter into parts of the environment where they were not intended. Starch encapsulation of pesticides has been proposed as a way of modifying pesticide behavior in the soil environment. This study was conducted to assess how starch encapsulation and temperature affect volatilization of atrazine 16-chloro-N-ethyl-N'-(1-methyl-ethyl)-1,3,5-triazine-2,4-diamine] and alachlor 12-chloro-N-(2,6-diethylphenyl)N-(methoxymethyl)acetamide]. Volatilization was measured using agroecosystem chambers as model systems. Herbicides were applied at rates of 1.7 kg ha-1 for atrazine and 2.8 kg ha-1 for alachlor, as either a commercial formulation or a starch encapsulated formulation, to the surface of moist soils maintained at temperatures of 15, 25 and 35-degrees-C. Air was drawn through the chambers (2.5 m3 min-1) and herbicide in the vapor phase was trapped in polyurethane foam plugs. Volatilization of both herbicides increased as temperature increased. Volatilization of atrazine was less when applied as starch-encapsulated formulation than the commercial formulation. After 35 d cumulative volatilization of atrazine ranged from < 1% of that applied as starch-encapsulated formulation at 15-degrees-C, to 14% of that applied as the commercial formulation at 35-degrees-C. Cumulative volatilization of alachlor was greater when applied as starch-encapsulated formulation than as the commercial formulation. After 35 d, cumulative volatilization of alachlor ranged from >2% of that applied as either formulation at 15-degrees-C to 32% of that applied as starch encapsulated formulation at 35-degrees-C. Differences in volatilization behavior between these herbicides are likely to be due to differences in chemical properties of these herbicides.