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

Abstract

Abstract 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 NH 4 NO 3 . Seasonal soil NO 3 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 NO 3 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 NO 3 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.