ARS | Publication request: SIMULATING NITRATE LOSSES FROM WALNUT CREEK WATERSHED

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: September 20, 2001
Publication Date: N/A

Technical Abstract: Calibration and evaluation of the Root Zone water Quality Model (RZWQM98) using field measured data from different geographical locations, is an important component of model improvement strategy. This study was designed to evaluate the latest version of RZWQM98 using six years (1992- 97) of field measured data from a sub-basin in Walnut Creek Watershed located in central Iowa. The measured data included subsurface drain or "tile" flows, nitrate-nitrogen (NO3-N) concentrations and loads with tile water and corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) yields. The dominant soil within this sub-basin 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 tile flow (mm) closely matched observed data with a model efficiency of 99% (EF=0.99), and the difference of 0.6% (D=0.6), between measured and predicted values. The model simulated NO3-N losses (kg ha**-1) with tile water reasonably well with EF=0.77 and D=11. Nitrogen-scenario simulations demonstrated that corn yield response function reached a plateau when N-application exceeded 90 kg ha**-1. Fraction of the applied nitrogen lost with subsurface drain water varied from 7 to 16% when N-application rate varied from 0 to 180 kg ha**-1 after accounting for the nitrate loss with no-fertilizer application. RZWQM has the potential to simulate the impact of nitrogen application rates on corn yields and NO3-N losses with subsurface drain flows for different agricultural fields.