A soil-column laboratory experiment and a 2-yr field-sampling study evaluated the overall dissipation of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide]. Theses studies also measured the effect of no-till and chisel-plow tillages on alachlor leaching and dissipation. 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-fill soil, alachlor dissipated slightly faster, and more was transported into the 10 to 30 cm soil layer. Weather conditions promoting the movement of alachlor into the soil, however, weakened the effect of tillage on the dissipation rate. Most of the alachlor present in the soil, regardless of tillage, was found in the top 10 cm at all times. Of the alachlor applied to 30-cm tall soil columns, only 0.4% was removed by water flowing from chisel-plow columns and 1.6% from no-till columns. The results show that tillage was not a key factor in alachlor dissipation and leaching. Alachlor leaching was also a minor component in overall dissipation.
Journal paper no. J-16594 of the Iowa Agric. and Home Economics Experiment Stn., Ames, IA 50011. Project no. 3003. This research was funded by the Leopold Center for Sustainable Agriculture, Ames, IA, and the CSRS-USDA Project on Management Systems Evaluation Areas (MSEA). Work was done at Iowa State Univ., Ames, IA 50011.