Sensitivity analysis of the root zone water quality model

The long-term goal of this research is to improve tools for predicting wate r quality in agricultural watersheds with significant sub-surface drainage. Specifically, USDA-ARS' Root Zone Water Quality Model (RZWQM) was investig ated as a tool for predicting the effects of agricultural management practi ces on nitrate loads in tile drainage in east central (Illinois. Sensitivit y of the model was explored to identify, those input parameters with the gr eatest influence on tile flow, nitrate in tile drainage, and crop yield. St udies were made within the contexts of two hydraulic descriptions of a silt y clay loam soil and two crops, corn and soybeans. Simulated tile flow prov ed to be most sensitive to drain spacing and soil hydraulic properties. In addition to the parameters affecting tile flow tile nitrate-N was also grea tly influenced by soil macroporosity. Biomass required to achieve a leaf ar ea index of 1.0 had the greatest impact on crop yield. More information is needed regarding the statistical distributions of the input parameters. If the model is to be used to predict nitrate loads in tile drainage, particul ar care should be taken in selecting saturated lateral hydraulic conductivi ty and Brooks-Corey soil properties.