RUNOFF AND LEACHING OF ALACHLOR UNDER CONVENTIONAL AND SOIL-SPECIFIC MANAGEMENT

The influence of conventional and soil-specific management on leaching and runoff losses of soil-applied alachlor (2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide) was studied across a soil catena (landscape) with varied slope and drainage characteristics. The catena consisted of: a well-drained Ves (fine-loamy, mixed, mesic Udic Haplustoll) soil on the backslope (1-4%), a Ves soil on the sideslope (6-12%), and a poorly drained Webster (fine-loamy, mixed, mesic Typic Haplaquoll) soil on the toeslope (0-3%). In general, the concentration of alachlor in runoff water was greater in the Ves soil than in the Webster. In 1992 alachlor concentrations in runoff (water, sediment + water) were less for soil-specific rates (2.20 or 2.80 kg/ha) than for a uniform rate (3.36 kg/ha) in both Ves soils. There was no significant difference in alachlor concentration related to application rates (soil-specific rate 3.66 kg/ha) in the runoff from the Webster soil. Averaged across soils and events, the concentrations of alachlor in runoff (water, sediments + water) were less for soil-specific rates than for the uniform rate. Alachlor was not detected in soil samples obtained from depths greater than 15 cm in any soil or treatment after the first sampling. At the first sampling in 1992 (7 days after application) alachlor was detected down to 45 and 90 cm in the Ves and Webster soils, respectively. Detectable amounts (greater-than-or-equal-to 0.1 mug/1) of alachlor were observed in soil water samples extracted from all three soils during some sampling dates. No particular trends were observed with soils or application rates.