Modeling the impact of conservation tillage practices on pesticide concentrations in ground and surface waters

Abstract

To analyze the environmental fate and migration of pesticides applied to croplands as they are affected by conservation tillage practices, pesticide models for leaching, surface water and ground water were selected and an application method was developed. Fourteen different pesticides applied to corn and soybeans were analyzed to determine probable concentrations in ground water and surface water under conventional tillage, reduced tillage and no tillage practices; the Lake Erie Basin was the study site. Surface runoff loadings and concentrations decreased under the conservation tillage scenarios, but ground water loadings and concentrations increased as a result of the decreased runoff and increased ground water recharge. Reduced tillage decreased surface runoff loads and concentrations by about 50% as compared with conventional tillage, and no tillage resulted in another 20% reduction. The pesticides with the highest surface runoff loads and concentrations were those with Koc values generally less than 200 ml g−1 and root zone half-lives greater than 40 d. For ground water, only four pesticides demonstrated mean annual loadings high enough to require estimation of resulting ground water concentrations. These four compounds also had the highest surface water loadings and are characterized by Koc values of 100 ml g−1 or less and root zone half-lives of 35 d or longer. Ground water concentrations for all four compounds were low, with carbofuran showing the highest concentrations (approaching 1.0 ppb). Next was dicamba, but its concentrations were four to five orders of magnitude less. Sensitivity analyses for carbofuran indicated that the concentrations could be at least one order of magnitude higher, depending on assumptions related to decay rate, hydraulic conductivity and other hydrogeologic parameters.