Jabro et al., 1993; Jemison et al., 1994; Lengnick and Fox, 1994). Most of the evaluation studies have cali-Nitrate leached from soils can contaminate drinking water and brated a model with an individual data set and then pose a health risk at concentrations Ͼ 10 mg N L Ϫ1 . Computer models conducted a validation with additional independent data may be useful management tools for estimating NO 3 leaching, but they need to be calibrated and validated before use. The objective sets. Calibration of the model has been typically accomof this work was to calibrate and validate LEACHN to simulate soil plished by adjusting input parameters and rate constants NO 3 , soil NH 4 , water drainage, and NO 3 leaching in a Cecil sandy so that output values are as close as possible to measured loam (fine, kaolinitic, thermic Typic Kanhapludults). The calibration values in the calibration data set. This approach to testwas done by determining rate constants and parameters under laboraing a model has the disadvantage of requiring a calibratory conditions. The validation data was obtained from a two-year tion data set. In addition, the approach can be very timestudy with conventionally tilled corn (Zea mays L.) during summer consuming, especially if the range of values explored for and either a rye (Secale cereale L.) cover crop or fallow conditions each input parameter and rate constant is relatively during winter. Water drainage collected by tiles was automatically large. Furthermore, since this process adjusts several measured, subsampled, and analyzed for inorganic N concentrations.input parameters and rate constants at the same time, During the cold season, LEACHN underestimated soil NH 4 and NO 3 in at least half of the cases. During the warm season, the model
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