Calibration of the root zone water quality model for simulating tile drainage and leached nitrate in the Georgia Piedmont

Calibration procedures and data used to parameterize a model, including model components that may or may not have been addressed, are generally not well documented in modeling studies. A comprehensive description of the process and parameters used for calibrating the Root Zone Water Quality Model, v. 1.3.2004.213, is presented in this article. The model was calibrated to simulate tile drainage and leached nitrate under conventional tillage management practices for maize (Zea mays L.) production followed by a rye (Secale cereale L.) cover crop in Cecil soils (kaolinitic, thermic, Typic Kanhapludults), and for cotton (Gossypium hirsutum L.) development in the Georgia Piedmont. Tile drainage and nitrate leaching were simulated within 15% of the observed values in the calibrated maize scenarios with and without the soil macroporosity option. Simulated and observed tile drainage and leached nitrate were not significantly different, and the simulated values were not significantly different with and without the macroporosity option. Simulated cotton biomass and leaf area index were well correlated with observed biomass and leaf area index until the last 21 d of the reproductive stage. Simulated and observed cotton water use were different by < 1 mm d(-1) based on A soil water in a 60-cm, profile during the critical peak bloom period. A detailed analysis of the calibration procedure and parameters used in this study will aid subsequent users of the model as well as aid in a subsequent evaluation of the model's performance for simulations of tile drainage and nitrate leaching in Georgia Piedmont cotton production systems.