ALACHLOR BIOTRANSFORMATION AND SORPTION IN SOIL FROM 2 SOYBEAN TILLAGE SYSTEMS

Few studies have investigated tillage effects on alachlor [2-chloro-N- (2, 6-diethylphenyl)-N-(methoxymethyl)acetamide] degradation. Objectiv es here were to evaluate kinetics and mechanisms of alachlor degradati on in surface (0-5 cm) Dundee silt loam (fine-silty, mixed, thermic, A eric Ochraqualf) from plots managed for 7 years as conventional tillag e (CT) or no-tillage (NT) soybeans (Glycine max L.). In experiment I, incubations ranged from 0 to 54 days after C-14-ring-labeled alachlor (4.44 mu mol kg(-1)) application. In experiment II, soil was incubated (10 g:3 mL of CaCl2) with C-14-labeled alachlor (14.8 or 111.2 mu mol L(-1)) from 1 to 25 days. Soils in experiment I were extracted with m ethanol and in experiment II were sequentially desorbed with 0.01 M Ca Cl2 and methanol and then oxidized to measure unextractable C-14. Mine ralization of alachlor was more rapid in NT. Methanol-extractable and CaCl2-desorbable alachlor declined during incubation for both tillage treatments, with a corresponding increase in methanol-unextractable C- 14. Tillage did not influence the initial disappearance of alachlor (h alf-life approximate to 6.5 days) but did affect metabolite transforma tions. Alachlor sorption was more rapid in NT, accompanied by less CaC l2-desorbable and more methanol-extractable alachlor and metabolites. Unextractable C-14 was also greater in the NT soil. Acidic metabolites accumulated in both tillage soils.