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Title: Evaluation of the RZWQM for simulating tile drainage and leached nitrate in the Georgia Piedmont

item Abrahamson Beese, Deborah
item Steiner, Jean
item Endale, Dinku

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2005
Publication Date: 5/3/2006
Citation: Abrahamson Beese, D.A., Radcliffe, D.E., Steiner, J.L., Cabrera, M.L., Endale, D.M., Hoogenboom, G. 2006. Evaluation of the RZWQM for simulating tile drainage and leached nitrate in the Georgia Piedmont. Agronomy Journal. 98:644-654.

Interpretive Summary: Scientists at the USDA-ARS-J.Phil Campbell, Sr. Natural Resource Conservation Center in Watkinsville, Georgia and the University of Georgia in Athens recently evaluated the impacts of tillage and no tillage agricultural management practices on movement of water through the soil. Understanding how agriculture influences water movement on and in the soil is important because this directly influences the quantity and quality of water available for other uses like drinking water and recreation. A computer model was used to predict how much fertilizer nitrogen was used by a cotton crop and how much would be carried by the drainage water into ground water. Too much nitrate can affect our health, and the model can help us understand how much fertilizer should be applied and how much could be lost into the ground water. We compared measured values of water drainage and nitrate loss in the drainage water to values predicted by the Root Zone Water Quality model. The model predicted more drainage and nitrate loss than we measured for all of the management treatments This model can be improved based on the results from this analysis. Further improvements to the model to better predict drainage and nitrate leaching can help farmers and producers manage crops and soils to keep our water clean. Improving the model will also help scientists better understand how to improve different agricultural management practices to protect water quality.

Technical Abstract: Models have become an important tool for evaluating the impact of agricultural management practices on water quality. We evaluated the utility of the Root Zone Water Quality Model (v. 1.3.2004.213) for simulating tile drainage and nitrate leaching under conventional and no tillage management practices in cotton production (Gossipium hirsutum L.) and rye (Secale cereale L.) cover cropping practices in a Cecil (kaolinitic, thermic, Typic Kanhapludult) soil in Georgia, USA. We calibrated the model for tile drainage and nitrate leaching, and for cotton development and water use based on experimental data collected at the J. Phil Campbell, Sr. Natural Resource Conservation Center at Watkinsville, Georgia from 1991 through 1993. Evaluation of the model with an independent data set from 1997 through 1998 resulted in measured and simulated tile drainage differences of 1074 mm for conventional tillage and 843 mm for no tillage treatments. Measured and simulated values of leached nitrate in tile drains were different by 30 kg ha-1 and by 37.5 kg ha-1 for the tillage treatments. The calibrated value for the ground water leakage rate worked well for the model calibration period. However, differences in simulated evapotranspiration and the effects of winter cover cropping during the four-year period at the study site since the model was calibrated affected the amount of soil water and soil nitrate available for tile drainage and nitrate leaching for the current study.