Evaluation of Poultry Litter Application Best Management Practices (BMPs) to Minimize Phosphorus Loss Using the Apex Model.

Developing best management practices to decrease phosphorus (P) loss from agricultural fields is an important environmental and agricultural priority. However, field-scale studies to evaluate P loss are expensive and time consuming and results are highly dependent on the weather patterns.  Simulation models offer an alternative method to evaluating BMP performance and are not subject to the same time, expense, or weather constraints of field studies.  The objective of this study was to determine the optimal timing, frequency, and rate for poultry litter applications to row-crop production systems using the Agricultural Policy/Environmental Extender (APEX) model.  The APEX model was calibrated and validated for runoff, sediment, and P loss from a clay-pan soil in South-East Kansas based on the Nash Sutcliffe efficiency (NSE), coefficient of determination (r²), and percent bias. The fully calibrated model was used to evaluate the effect of litter application timing (spring vs. fall), frequency (one, two, or four applications in a four-year rotation), and rate on P loss. APEX calibration provided satisfactory event-based calibration for runoff, sediment loss, and phosphorus loss.  The calibrated model was used to simulate P loss for 100 different weather scenarios for each combination of rate, timing, and frequency. The results can be used by producers in the region to help them minimize P loss to receiving waters when applying poultry litter.