Agricultural conservation practices are commonly implemented in watersheds to reduce sediment and nutrient losses from agricultural lands and improve surface water quality. While the effectiveness of practices in reducing sediment and nutrient losses has been quantified by numerous multi-agency programs and peer-reviewed studies, similar standardized effectiveness measures and tools are yet to be fully implemented in evaluating benefits of such practices in reducing pesticide losses. The adoption of a stewardship evaluation approach similar to established approaches for nutrients will lead to a scientifically rigorous yet simple to apply methodology that documents how farmer actions can directly translate to quantifiable reductions in off-target pesticide transport and subsequent water quality improvements. We aim to develop a web-based tool capable of evaluating the impacts of field and farm-level practices on off-field pesticide transport to derive metrics for quantifying environmental stewardship. The tool will utilize the US Department of Agriculture (USDA) Agricultural Policy / Environmental eXtender Model (APEX), a well-established, physically-based model that predicts the short and long-term impacts of agronomic management decisions on environmental quality. This phase of tool development focused on designing the APEX pesticide transport modeling approach including determination of the necessary pesticide application inputs, cropping cycle input options, conservation/stewardship practice options, and how the off-target pesticide transport and reductions will be quantified. Model test scenarios were developed to evaluate model behavior and compare the predictions of off-site pesticide transport reductions with expected values from the peer-reviewed literature. A subset of simulations were set up to mirror standard regulatory PRZM scenarios and results compared across models. The long-term vision is that outputs from the web-based tool, relative pesticide load reductions estimated from conservation practice implementation, could be incorporated into the regulatory modeling framework to quantify the water quality improvements realized in the context of FIFRA registration decisions and endangered species effects determinations.

APEX simulations to evaluate effectiveness of field-Level conservation practices in reducing off-field pesticide transport for a stewardship assessment tool

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