Evaluation of root zone water quality model for simulation of nonpoint source pollution from agricultural lands

摘要

Calibration and evaluation of the Root Zone Water Quality Model (RZWQM98), using measured data from different geographical locations, is an important component of model improvement strategy. This study was designed to evaluate the latest version ofRZWQM98 using 6 yr (1992-97) of field-measured data from a field at Walnut Creek Watershed located in central Iowa. Measured data included subsurface drainage or 'tile 'flows, nitrate-nitrogen (NO_3-N) concentrations and loads with subsurface drainage water, and corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) yields. The dominant soil within this field was Webster Soil (fine-loamy) in the Clarion-Nicollet-Webster Soil Association. The cropping system was a corn-soybean rotation with chisel plowing after corn harvest. Simulations of subsurface drainage flow (mm) closely matched observed data showing model -efficiency of 99 percent (EF = 0.99), and difference of 0.6 percent (D = 0.6), between measured and predicted values. The model simulated NO_3-N losses (kg ha~(-1)) with subsurface drainage water reasonably well with EF = 0.77 and D = 11. The simulated corn and soybean yields (kg ha~(-1)) were in close agreement with measured data with D = 5. Nitrogen-scenario simulations demonstrated that corn yield response function reached a plateau when N-application rate exceeded 90 kg ha~(-1). Fraction of applied nitrogen lost with subsurface drainage water varied from 7 to 16 percent when N-application rate varied from 0 to 180 kg ha~(-1) after accounting for the nitrate loss with no-fertilizer application. The RZWQM98 has the potential to simulate the impact of nitrogen application rates on corn yields and NO_3-N losses with subsurface drainage flows for different agricultural fields.