Effect of tillage on atrazine bioavailability

Abstract

Studies were conducted to determine atrazine sorption (partitioning), bioavailability (soil solution concentrations), and dissipation in the top 0 to 1.5, 1.5 to 3, and 3 to 5 cm of soil as a function of tillage. Paired microplots (plow-till vs no-till) were established in replicated long-term tillage field plots, such that treatments included 4-year plow-till, 4-year no-till, 1-year plow-till, and 1-year no-till. Organic carbon content in the top 0 to 1.5 cm was about 75% greater in 4-year no-till soil than in 4-year plow-till soil; at lower depths, organic carbon contents were consistently lower in 4-year no-till soil. Soil solution concentrations of atrazine in the top 0 to 1.5 cm of soil were approximately twofold lower in 4-year no-till soil than in 4-year plow-till soil (5.4 μg mL-1 vs 10.1 μg mL-1) 8 days after application. This was caused by increased sorption and higher gravimetric moisture contents. Soil solution concentrations of atrazine in the 1.5 to 3- and 3 to 5-cm soil depths were also lower in 4-year no-till soil compared with plow-till soil, apparently as a result of increased leaching in plow-till. Soil solution concentrations for 1-year plow-till and 1-year no-till soils were intermediate. Relative percentages of atrazine recovered in the top 5 cm of soil were comparable with tillage treatments (> 80%) through Day 21, indicating that the bulk of atrazine remained within the zone of weed germination. Rates of dissipation and leaching (0-5 cm) were comparable for plow-till versus no-till soil. These data indicate that atrazine bioavailability is diminished significantly in no-till soils, which may contribute to losses of atrazine efficacy.