ALACHLOR DISSIPATION IN SHALLOW CROPLAND SOIL

A soil-column laboratory experiment and a 2-yr field-sampling study ev aluated the overall dissipation of alachlor [2-chloro-N-(2,6-diethylph enyl)-N-(methoxymethyl) acetamide]. Theses studies also measured the e ffect of no-till and chisel-plow tillages on alachlor leaching and dis sipation. In the top 30 cm layer of soil, the overall half-life was 3 d or less, and the time to 90% dissipation ranged from 17 to 30 d, In no-till soil, alachlor dissipated slightly faster, and more was transp orted into the 10 to 30 cm soil lager. Weather conditions promoting th e movement of alachlor into the soil, however, weakened the effect of tillage on the dissipation rate. Most of the alachlor present in the s oil, regardless of tillage, was found in the top 10 cm at all times. O f the alachlor applied to 30-cm tall soil columns, only 0.4% was remov ed by water flowing from chisel-plow columns and 1.6% from no-till col umns. The results show that tillage was not a hey factor in alachlor d issipation and leaching. Alachlor leaching was also a minor component in overall dissipation.