Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/12/1997
Publication Date: N/A
Citation: Interpretive Summary: To reduce production costs and maintain farm profitability, many dairy farmers in the northeast U.S. are increasing their reliance on pasture as a means to provide forage to their milking cows. But if the number of cows on pasture on each farm is too high, nitrate contained in cow urine can leak through soil and into the ground water in amounts that can significantly harm water quality. Research is being conducted on a limite number of representative northeastern U.S. soil types to measure the amount of nitrate that can leak through soils and into the ground water. However, there are many soil types in the northeastern U.S. Computer models, such as NCSWAP, provide a means to extrapolate the experimental data collected on one soil to other soils in the northeastern U.S. In this experiment we tested NCSWAP using data collected on one soil type and found that it was able to predict the amount of nitrate from cow urine that would leak through the soil and into the ground water. As data becomes available fro other soils, NCSWAP and other models will be tested to determine their suitability for developing techniques to determine the number of animals that can be kept on a pasture without doing undue harm to water quality.
Technical Abstract: The accuracy of the NCSWAP model to simulate nitrate leaching from orchardgrass pasture was evaluated using field data collected from a 3-year leaching experiment conducted in central Pennsylvania on Hagerstown silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate leaching losses below the 1-m depth from N-fertilized orchardgrass sod were measured with intact soil core lysimeters (0.6-m dia. by 1-m long). Five N fertilizer treatments consisted of a control, urine application in the spring, urine application in the summer, urine application in the fall, and feces application in the summer were used to test the model. The model was calibrated using the data from 1993-94 and then was validated using 1994-95 and 1995-96 water flow and nitrate leaching data. Statistical analysis indicated a good fit between field measured and predicted nitrate leaching for most treatments in each year. The model simulations of water flow and nitrate leaching losses below the 1-m depth were compared with the mean of measured field data for these three years. The results of this study showed that the NCSWAP model performed well and accurately simulated water flow and total annual NO3-N loss through leaching below the 1-m depth under orchardgrass pasture. However, the model failed to produce accurate simulations for the feces treatment in 1994-95. The simulation error in the feces treatment seemed to be related to N mineralization process in the model. Generally, the results of this study suggest that the NCSWAP model can be used for predicting NO3-N leached annually from pastured orchardgrass.