Atrazine runoff from conservation tillage systems: A simulated rainfall study

Atrazine losses in surface runoff from a silty clay loam under no-till (NT) chisel (CH) and disk (DY) tillage were measured using simulated rainfall. Atrazine (0.56 kg ha(-1); 0.50 lb acre(-1)) and rainfall (64 nm h(-1), 2.5 in h(-1), for 1.25 hr) were applied to small plots and atrazine in sediment and dissolved in water was determined for all runoff samples. Total atrazine losses were CH (58.6 g ha(-1)) > NT (44.1 g ha(-1)) = DK (41.9 g ha(-1)). However, sediment losses were CH (2.84 MT ha(-1)) > DK (2.09 MT ha(-1)) congruent to NT (0.37 MT ha(-1)). Dissolved atrazine in runoff water accounted for more than 99.8% of total atrazine loss, and atrazine lost through sediment transport was insignificant Although atrazine partitioning between solution and solid phases in soil ir often directly related to soil organic matter content atrazine adsorption by soil organic matter did not control the amount of atrazine last in runoff. Poor relationships between apparent Kd values and soil organic matter content across simulated rainfall studies suggest experimental conditions affect runoff losses of atrazine more than atrazine adsorption by soil organic matter No-till systems reduce water and herbicide runoff under natural rainfall conditions, but results under simulated rainfall conditions are mixed. Presaturation of plots with water, high-intensity simulated rainfalls shortly after atrazine application and other experimental renditions may outweigh tillage effects and mask differences in atrazine losses from land under different tillage systems. Future best management practices (BMPs) used to reduce herbicide runoff from agricultural land will be developed from simulated rainfall studies Identification of successful BMPs that minimize herbicide runoff under environmental conditions requires careful selection of experimental conditions used in simulated rainfall studies.