title: Field evaluation of a model for predicting nitrogen losses from drained lands.
abstract: The N simulation model, DRAINMOD-N II, was field-tested using a 6-yr data set from an artificially drained agricultural site located in eastern North Carolina. The test site is on a nearly flat sandy loam soil which is very poorly drained under natural conditions. Four experimental plots, planted to a corn (Zea mays)-wheat (Triticum aestivum L.)-soybean (Glycine max.) rotation and managed using conventional and controlled drainage, were used in model testing. Water table depth, subsurface drainage, and N concentration in drain flow were measured and meteorological data were recorded continuously. DRAINMOD-N II was calibrated using the data from one plot; data sets from the other three plots were used for model validation. Simulation results showed an excellent agreement between observed and predicted nitrate-nitrogen (NO(3)-N) losses in drainage water over the 6-yr period and a reasonable agreement on an annual basis. The agreement on a monthly basis was not as good. The Nash-Sutcliffe modeling efficiency (EF) for monthly predictions was 0.48 for the calibration plot and 0.19, 0.01, and -0.02 for the validation plots. The value of the EF for yearly predictions was 0.92 for the calibration plot and 0.73, 0.62, and -0.10 for the validation plots. Errors in predicting cumulative NO(3)-N losses over the 6-yr period were remarkably small; -1.3% for the calibration plot, -8.1%, -2.8%, and 4.0% for the validation plots. Results of this study showed the potential of DRAINMOD-N II for predicting N losses from drained agricultural lands. Further research is needed to test the model for different management practices and soil and climatological conditions.
authors.affiliation: Department of Biological and Agricultural Engineering., North Carolina State University, Raleigh, NC 27695, USA. mohamed_youssef@ncsu.edu
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Youssef
authors.forename: R Wayne
authors.initials: RW
authors.lastname: Skaggs
authors.forename: George M
authors.initials: GM
authors.lastname: Chescheir
authors.forename: J Wendell
authors.initials: JW
authors.lastname: Gilliam
mesh_terms: D000383:Agriculture; D002138:Calibration; D004784:Environmental Monitoring; D005308:Fertilizers; D005544:Forecasting; D008954:Models, Biological; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000032:analysis*; D009657:North Carolina; D012989:Soil Pollutants / Q000032:analysis*; D013025:Glycine max; D013997:Time Factors; D014908:Triticum; D014873:Water Pollutants / Q000032:analysis*; D014881:Water Supply; D003313:Zea mays
chemical_list: D005308:Fertilizers; D009566:Nitrates; D012989:Soil Pollutants; D014873:Water Pollutants; D009584:Nitrogen