Evaluating Agricultural Management Effects on Alachlor Availability: Tillage, Green Manure, and Biochar

Agricultural and soil management practices have been reported to affect alachlor sorption-desorption and degradation rates. Though alachlor has been banned in the E.U. since 2006, it is still used in U.S. corn and soybean production. The objectives of this study were to: (a) assess differences in alachlor sorption due to tillage treatments (chisel plow and ridge tillage) on soils from three midwestern U.S. locations; and (b) determine the effect of various soil amendments on the sorption-desorption and mineralization of alachlor. Soils were amended at a rate of 10% (w/w) with biochars derived from soybean stover, sugarcane bagasse, and wood chips, as well as the uncharred feedstock materials. Sorption-desorption studies were performed using the batch equilibration method, and alachlor mineralization was evaluated in a 30-day incubation. Tillage management did not affect alachlor sorption to soil across the three sites, despite the fact that the tillage operations were imposed for 4 years (p > 0.05). While the sorption coefficient (K-d) values for alachlor were relatively low in the three unamended soils (K-d = 1.76, 1.73, and 1.15 L.kg(-1) for IL, MN, and PA soils, respectively), biochar amendments increased alachlor sorption between 4x and 33x compared to the unamended soil. The amendments also affected alachlor mineralization such that degradation was slower in both biochar- and raw feedstock-amended soils. Based on these results, biochar additions are expected to affect the availability of alachlor for transport and degradation. Furthermore, this study highlights the larger impact of biochar addition than tillage practices on altering immediate alachlor sorption capacities.