NITRATE LEACHING FROM SOIL CORE LYSIMETERS TREATED WITH URINE OR FECES UNDER ORCHARDGRASS - MEASUREMENT AND SIMULATION

The ability of the N submodel, LEACHN, of the Leaching Estimation And CHemical Model (LEACHM model) to simulate nitrate-nitrogen (NO3-N) lea ching from orchardgrass (Dactylis glomerata L.) pasture was evaluated using field data from a 2-yr experiment, Leaching data were collected from an experiment conducted in central Pennsylvania on Hagerstown sil t loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate losses belo w the 1-m depth from N-fertilized orchardgrass sod were measured with intact soil core lysimeters (0.6-m diam, by 1-m long), Five N fertiliz er treatments consisted of a control, urine application in the spring, urine application in the summer, urine application in the fall, and f eces application in the summer. Calibration N transformation rate cons tants from previous work with inorganic fertilizer and manure treatmen ts under corn were used to evaluate the LEACHN model under pasture con ditions, Statistical analysis indicated that the model accurately pred icted annual NO3-N leaching below the 1-m depth for three to five of t he five treatments in each year. The model failed to produce accurate predictions for the control and feces treatments in 1993 to 1994. The simulation error in these two treatments appeared to be related to soi l N transformation rate constants in the model, Other reasons for disc repancies between measured and simulated NO3-N leaching for some month s may have been due to restricted water dow associated with frozen soi l or a heavy snowpack during winter. Results demonstrate the potential of the LEACHN model to predict NO3-N leaching under pasture condition s using N transformation rate constants determined through the calibra tion process from corn (Zea mays L.) fields on similar soils.