Nitrogen (N) rate, hybrid genetics, and planting density are among the main factors that a corn producer manages to achieve high yield. Because these factors are so paramount to corn grain yield, it is imperative to understand how they interact so that appropriate strategies can be devised to exploit their positive interactions in various crop management scenarios, and to understand how to best improve corn hybrids for responses to N and increased plant density.

Twelve corn hybrids were grown at two plant densities (76,600 and 104,000 plants ha^-1) and three N fertilizer rates (0, 67, and 252 kg N ha^-1) at Champaign-Urbana, IL in 2010 and 2011. The objective of this experiment was to understand interactions between plant density and N fertilizer rate in biotechnology trait enhanced corn hybrids. On average, increasing plant density resulted in a small decrease in grain yield in 2010. The response to increased plant density was most negative under unfertilized conditions, and increasing the rate of N promoted less negative or positive responses to plant density. Considerable genetic variation in plant density response was observed, and hybrids with positive responses to increased plant density appeared to be less sensitive to competition under low N conditions.

Three response patterns to N fertilizer were detected in the hybrids. These patterns are: (i) high check plot yield (yield without application of N) with a small response to fertilizer N, (ii) high check plot yield with a large response to fertilizer N, and (iii) low check plot yield with a large response to fertilizer N. High check plot yield hybrids had increased kernel number and individual kernel weight under low N relative to the low check plot yield hybrids. Increasing the N rate promoted an increase in kernel number and individual kernel weight in all three response patterns; however, a large response to fertilizer N appeared to be related to greater post-flowering N uptake.

In general, the results of this experiment suggest that hybrids with a positive response to increased plant density possess higher check plot yields (i.e., tolerance to N deficiency), and increased fertilizer N responses relative to hybrids that perform poorly with increased plant density.