Abstract:

Agriculture in the Midwest US faces the formidable challenge of improving crop productivity, while simultaneously mitigating the environmental consequences of intense management. This study examined the simultaneous response of nitrate-nitrogen (NO3-N) leaching losses and maize (Zea mays L.) yield to varied fertilizer-N management using field observations and the IBIS model. The model was validated against 6 yr of field observations in maize plots receiving an optimal (180 kg N ha-1) fertilizer-N application and in N-unfertilized plots on a silt loam soil near Arlington, Wisconsin. Predicted values of grain yield, harvest index, plant N uptake, residue C:N ratio, LAI, grain-N, and drainage were within 20% of observations. However, simulated NO3-N leaching losses, NO3-N concentrations, and net N-mineralization exhibited less interannual variability than observations, and had higher levels of error (20-65%). Potential impacts of 30% higher (234 kg N ha-1) and 30% lower (126 kg N ha-1) fertilizer-N use (from optimal) on NO3-N leaching loss and maize yield were simulated. A 30% increase in fertilizer-N use increased annual NO3-N leaching by 56%, while yield increased by only 1%. The NO3-N concentration in the leachate solution at 1.4 m below the soil surface was 30.7 mg L-1. When fertilizer-N use was reduced by 30% (from optimal), annual NO3-N leaching losses declined by 42% after 7 years, and annual average yield only decreased by 8%. However, NO3-N concentration in the leachate solution remained above 10 mg L-1 (11.3 mg L-1). Clearly, non-linear relationships existed between changes in fertilizer use and NO3-N leaching losses over time. Simulated changes in NO3-N leaching were greater in magnitude than fertilizer-N use changes.