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Nitrate Leaching from Soil Core Lysimeters Treated with Urine or Feces under Orchardgrass: Measurement and Simulation

Dep. of Agronomy, 116 A.S.I. Bldg., Penn State Univ., University Park, PA 16802

W. L. Stout

USDA-ARS Pasture Systems and Watershed Management Res. Lab., University Park, PA 16802

^* Corresponding author (jau{at}psu.edu).

ABSTRACT

The ability of the N submodel, LEACHN, of the Leaching Estimation And CHemical Model (LEACHM model) to simulate nitrate-nitrogen (NO₃-N) leaching 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 silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate losses below 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 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. Calibration N transformation rate constants from previous work with inorganic fertilizer and manure treatments under corn were used to evaluate the LEACHN model under pasture conditions. Statistical analysis indicated that the model accurately predicted annual NO₃-N leaching below the 1-m depth for three to five of the 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 soil N transformation rate constants in the model. Other reasons for discrepancies between measured and simulated NO₃-N leaching for some months may have been due to restricted water flow associated with frozen soil or a heavy snowpack during winter. Results demonstrate the potential of the LEACHN model to predict NO₃-N leaching under pasture conditions using N transformation rate constants determined through the calibration process from corn (Zea mays L.) fields on similar soils.