Variability in Corn Yield Response to Nitrogen Fertilizer in Eastern Canada

Corn (Zea mays L.) yield response to N has been found to vary spatially within a field. The objective of this study was to examine how grain corn yield response to N varies with planting date, soil texture, and spring weather across sites and years in the Monteregie region. Trials were conducted from 2002 to 2004 and 2006 to 2010, at 11 sites with 23 hybrids and four N application rates, for a total of 45 site-years. Each site-year involved five or six N rates ranging from 80-90 to 240 kg N ha(-1). Grain yield response to N rates varied among site-years. Trials were separated into two groups based on optimal and late planting dates. Significant differences in grain yield among the applied N rates were observed in all of the site-years planted at optimal dates (from 8.8-14.7 Mg ha(-1)), and in most of those planted late (8.5-12.8 Mg ha(-1)). Economic optimum nitrogen rates (EONR) ranged less widely for site-years planted on optimal dates (180-237 kg N ha(-1)) than for those planted late (132-237 kg N ha(-1)). The EONR was affected by soil textural classes and rainfall. On coarse-textured soils, more N was needed to optimize grain yield in years with wet growing seasons. These results suggest that the current N recommendations for corn in Quebec should consider the variability in response associated with site-specific effects of planting date, soil texture, and weather.