PREVENTING PESTICIDE CONTAMINATION OF GROUNDWATER WHILE MAXIMIZING IRRIGATED CROP YIELD

A simulation/optimization model is developed for maximizing irrigated crop yield while avoiding unacceptable pesticide leaching. The optimiz ation model is designed to help managers prevent non-point source cont amination of shallow groundwater aquifers. It computes optimal irrigat ion amounts for given soil, crop, chemical, and weather data and irrig ation frequencies. It directly computes the minimum irrigated crop yie ld reduction needed to prevent groundwater contamination. Constraint e quations used in the model maintain a layered soil moisture volume bal ance; describe percolation, downward unsaturated zone solute transport and pesticide degradation; and limit the amount of pesticide reaching groundwater. Constraints are linear, piecewise linear, nonlinear, and exponential. The problem is solved using nonlinear programming optimi zation. The model is tested for different scenarios of irrigating corn . The modeling approach is promising as a tool to aid in the developme nt of environmentally sound agricultural production practices. It allo ws direct estimation of trade-offs between crop production and groundw ater protection for different management approaches. More frequent irr igation tends to give better crop yield and reduce solute movement. Tr ade-offs decrease with increasing irrigation frequency. More frequent irrigation reduces yield loss due to moisture stress and requires less water to fill the root zone to field capacity. This prevents the solu te from moving to deeper soil layers. Yield-environmental quality trad e-offs are smaller for deeper groundwater tables because deeper ground water allows more time for chemical degradation.