|Jabro, Jalal "jay"|
Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2006
Publication Date: 6/6/2006
Citation: Jabro, J.D., Jabro, A.D., Fox, R.H. 2006. Accuracy and performance of three water quality models for simulating NO3-N losses under corn. Journal of Environmental Quality. 35:1227–1236.
Interpretive Summary: The capabilities of three water quality computer models LEACHM, NCSWAP, and SOILN to simulated NO3-N leaching past 1.2 m from N-fertilized and manured corn were evaluated and compared. The models simulations of NO3-N leaching losses were compared with the mean of the zero –tension pan lysimeter field-measured values for each year. Statistical analyses suggest that LEACHM, NCSWAP, and SOILN models were able to provide accurate simulations of total annual NO3-N leached below the rootzone of corn for 8, 9, and 7 of 10 cases, respectively, in the validation years. The overall performance and accuracy of SOILN model was less than the LEACHM and NCSWAP models, as reflected by statistical results used in this study. The reason for the accuracy differences among these models may be related, in part, to N and C cycling and transformation incorporated in the code of the models. In general, statistical analyses suggest that the three water quality models performed well and were capable of successfully simulate annual NO3-N leaching losses below 1.2 m depth without the need for recalibration from year to year.
Technical Abstract: Computer simulation models can be used to predict N dynamics in soil-water-plant systems and may also be used to avoid excessive fertilizer input and hence to minimize leaching of nitrate-nitrogen (NO3-N) beyond the crop roozone. The simulation accuracy and performance of three water quality models (LEACHM, NCSWAP, and SOILN) to predict NO3-N leaching were evaluated and compared to field-measured data from a 5-year field experiment conducted on a Hagerstown silt loam (fine, mixed, mesic, Typic Hapludalf). Nitrate-N losses past 1.2 m from N-fertilized and manured corn (Zea mays L.) were measured with zero tension pan lysimeters (0.456 m2) for five years. The models were calibrated using field data for 1989-90 and validated using 1988-89, 1990-91, 1991-92, and 1992-93 NO3-N leaching data. Statistical analyses indicated that LEACHM, NCSWAP, and SOILN models were able to provide accurate simulations of total annual NO3-N leaching losses below the 1.2 m depth for 8, 9, and 7 of 10 cases, respectively, in the validation years. The inaccuracy in the models’ annual simulations for the control and manure treatments seems to be related to inadequate description of N and C transformations, processes and pools incorporated in the code of the models. The overall performance and accuracy of SOILN model was less than the LEACHM and NCSWAP models, as reflected by statistical results used in this study. The RMSE and EF were 10.7, 0.9; 9.5, 0.93; and 20.7, and 0.63 for LEACHM, NCSWAP, and SOILN, respectively. Based on this statistical analysis, the three water quality models have the potential to predict the fate of fertilizer or manure nitrogen added to corn in relation to NO3-N leaching losses below 1.2 m depth without recalibration of models from year to year.