Evaluation of the Root Zone Water Quality Model (RZWQM) for Southern Ontario: Part II. Simulating Long-Term Effects of Nitrogen Management Practices on Crop Yield and Subsurface Drainage Water Quality

Abstract

Abstract Loss of nitrogen from the agricultural production system is of concern in Ontario. The challenge for researchers and farmers is to fulfill crop water requirements while limiting chemical movement with surface and subsurface runoff. The main objective of this study was to evaluate the long-term effects of current N management practices for corn production for two different soil types using the Root Zone Water Quality Model (RZWQM) for southern Ontario conditions. The model simulated the amount of subsurface tile drainage, residual soil nitrate-nitrogen (NO3-N), NO3-N in subsurface drainage water, and crop yield. The validated RZWQM for silt loam and sandy loam soils showed that the relative long-term effectiveness of the most economic rate of nitrogen (MERN) for corn production fluctuates significantly from year-to-year in response to weather patterns. In addition, soil type had a small but significant effect on the MERN. Side-dress application of N on sandy loam resulted in significant reduction in corn yield and NO3-N loss to shallow groundwater. Also, crop rotation from corn-soybean to corn-soybean-soybean resulted in a greater reduction of NO3-N loads in the tile outflow on silt loam soil than on sandy loam soil. Overall, the RZWQM simulated tile drain flow, NO3-N loss, and crop yield with reasonable accuracy. However, more field work is needed to assist with identifying suitable values for a number of coefficients used in the RZWQM's nutrient component for Ontario conditions.