Date of Award
Doctor of Philosophy
Agricultural and Biosystems Engineering
Rameshwar S. Kanwar
LaDon C. Jones
Field and laboratory experiments evaluated the overall dissipation of alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide) and the effect of no-till and chisel-plow tillages on alachlor leaching and dissipation. In the top 30-cm layer of field soil, the time to 50% dissipation (half-life) was 2 to 3 d, and the time to 90% dissipation ranged from 17 to 30 d. In no-till soil, alachlor dissipated slightly faster, and more was transported into the 10-to-30-cm soil layer. The tillage effect depended on weather that favored movement into and dissipation within the soil, rather than dissipation on plant residues and the soil surface. Most of the alachlor, regardless of tillage, was in the top 10 cm at all times. Of the alachlor applied in the laboratory to soil columns, only 0.4% was removed by water flowing from chisel-plow columns and 1.6% from no-till columns. Tillage did not consistently influence alachlor dissipation. In both the field and laboratory studies, dissipation was faster than expected. From the literature, initial volatilization or wind-drift loss and subsequent microbial degradation appear to have been the major dissipation processes. A two-compartment model was developed to simulate this non-first-order dissipation and to incorporate the effects of precipitation, temperatures, crop and residue shading, and other environmental factors. The model requires only easily-collected weather, soil, and pesticide information and calculates the daily amount of alachlor and times for 50% and 90% dissipation. After calibration, the model predictions fit 2 years of field-sample data with reasonable accuracy. The half-life calculated by the model was 1 d for all years. Time to 90% dissipation was 18 d for 1992, 23 d in 1993, and 1.5 d for 1994. Environmental conditions influenced overall alachlor dissipation, while tillage and leaching did not.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Dee Anna Jo Weed
Weed, Dee Anna Jo, "Measuring and modeling alachlor dissipation in soil " (1995). Retrospective Theses and Dissertations. 11100.