EVALUATION OF NITROGEN VERSION OF LEACHM FOR PREDICTING NITRATE LEACHING

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Abstract
The abilities of the Richards and convectiondispersion equations approach (LEACHNR) and the capacity model approach (LEACHNA) of the nitrogen version (LEACHN) of the LEACHM model to simulate nitrate leaching were evaluated using field data from a 5-year nitrate leaching experiment conducted in central Pennsylvania on Hagerstown silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate leaching losses from N-fertilized and manured corn below the 1.2-m depth were measured with zerotension pan lysimeters. Three N-fertilized and manured treatments for 1988–1989, 1989–1990, and 1990–1991 and two N-fertilized treatments for 1991–1992 and 1992–1993 were used from the leaching experiment to evaluate both approaches of LEACHN. The individual monthly simulations of nitrate leaching were compared with the mean of pan efficiency corrected-measured data for these 5 years. Both approaches of the model were calibrated to the site conditions using the data of 1989–1990 and were then evaluated using 1988–1989, 1990–1991, 1991–1992 and 1992–1993 nitrate leaching data. Simulated results for the calibration year for both models were reasonably accurate (31 of 36 months simulated within the experimental 95% confidence limits). The statistical analysis used in this study indicated that both LEACHNA and LEACHNR adequately (91 to 120 months within the 95% confidence limits) predicted nitrate leaching below the 1.2-m depth for treatments in the refinement years. Much of the simulation error in some treatments in the refinement years seemed to be related to the sub-routine controlling soil nitrogen transformation processes and their rate constants in the model. The large deviations in NO−3-N leached in some winter months may be related, in part, to problems with simulated water flow associated with the frozen soil conditions and snow accumulation. The addition of a dual-pore water flow option (LEACHNA) to the nitrogen version of LEACHM did not improve prediction of nitrate leaching beyond the rooting zone of corn under Pennsylvania conditions. © Williams & Wilkins 1995. All Rights Reserved.
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