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Simulation by NCSWAP of Seasonal Nitrogen Dynamics in Corn: I. Soil Nitrate

USDA-ARS, Soil Microbial Systems Laboratory, Beltsville Agric. Res. Ctr., Beltsville, MD 20705
Dep. of Agronomy, Pennsylvania State Univ., University Park, PA 16802

^* Corresponding author.

Computer simulation models of crop—soil systems offer the potential to increase understanding of soil N cycle processes, thereby improving management of N resources in agricultural systems. NCSWAP (Nitrogen, Carbon, Soil, Water, And Plant) is a comprehensive, deterministic computer model of the plant-soil system that simulates seasonal soil C and N cycles under the control of temperature, moisture, microbial activity, and crop growth. The objective of this study was to validate NCSWAP using data collected during a 3-yr N-rate study in central Pennsylvania that investigated seasonal N dynamics in corn (Zea mays L.) provided with N as liquid dairy manure or as NH₄NO₃. Seasonal soil NO₃ concentration in the upper soil layer, seasonal aboveground N accumulation by corn, and water leached past 1.2 m during the second year of the study were used to calibrate input values controlling soil water flow and NO₃ production from mineralization of soil organic N sources. The validation of NCSWAP identified several limitations in the water flow and C and N cycling submodels as well as in the potential of the model to simulate seasonal N dynamics in corn. Validation simulations were about as accurate as calibration simulations, reflecting the ability of the model to simulate C and N dynamics without recalibration from year to year. Much of the simulation error was related to an overestimation of NO₃ leaching caused by the inability of the model's microporous flow submodel to simulate the macropore-influenced water flow in the well-structured soil used in the validation.

Received for publication May 4, 1992.

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