Characterization of Commercial Corn Hybrids in Response to Different Nitrogen Fertilizer Rates and Plant Populations.

Nitrogen (N) fertilizer rate and plant population are two important management factors determining corn yield.  The characterization of a corn hybrid’s response to N fertilizer rate, plant population and their relationship will support a farmer’s decision in selecting hybrids depending on the agronomic management conditions. In 2012 and 2013, sixty-four elite hybrids represented by different seed companies were tested at three different locations in Illinois under three N rates (0, 67, and 252 kg N ha^-1) and two levels of plant population (76,600 and 104,000 plants ha^-1). Yield response to different treatment combination was analyzed to identify the best ‘racehorse’ hybrids (characterized by high N and high plant population response) and ‘workhorse’ hybrids (characterized by high yield response under 0 N and high initial response to N). Yield and plant response to N and population were significantly higher in 2013 compared to 2012. There was a significant correlation between check plot yield (0 kg N ha^-1 at 76,600 plants ha^-1) and yield at high N (252 kg N ha^-1) and this correlation tended to be more significant in lower yield environments. Corn hybrids from different brands exhibited a diverse response to N and plant density in both years. Our research was able to identify ‘workhorse’ and ‘racehorse’ hybrids that are respectively highly responsive to management and N loss conditions. Current crop management practices used by most companies to select hybrids (252 kg N ha^-1 and 76,600 plants ha^-1) may not explain a hybrid’s performance under N loss conditions or under high plant population. The characterization of ‘racehorse’ and ‘workhorse’ hybrids may be an important tool to understand hybrid stability across different environmental conditions. Hybrids exhibiting both characteristics (high ‘racehorse’ and high ‘workhorse’) would be suitable for use under standard production conditions where N loss or N unavailability are prevalent, or under intensive management systems where higher plant populations and higher rates of N are used.