Hybrid and Plant Density Effects On Nitrogen Response in Corn.

The development of corn hybrids that may be improved for nitrogen use efficiency along with the emphasis on higher plant density for maximum yields of modern hybrids have raised questions about interactions between N rate and plant density.  We planted four hybrids (Pioneer 33D49, 33K44, 33W84, and 34F07) to represent a range of responses to N rate and plant density at four sites in Illinois at combinations of densities of 44,460, 83,980, and 123,500 plants/ha and N rates of 0, 90, 179, and 269 kg N/ha.  At two productive locations (DeKalb and Monmouth), the lowest density (44,460/ha) responded little to N rates above 90 kg/ha, and yields at the two higher N rates, and at the two higher densities, were nearly identical.  The Urbana site experienced very dry conditions and the Brownstown site was wet early and dry late.  At both of these sites, the two lower densities (44,460 and 83,980 plants/ha) produced higher yields than the highest density across all N rates.   At Urbana, there was little yield response to N rates above 90 kg N/ha at any plant density, while at Brownstown, yields responded linearly to N rate.  Hybrid responses to N rate-density combinations were inconsistent.  We found no support for the idea that increasing corn yields requires increases in both plant density and N rate.  These results advance our understanding of N rate-plant density response within varying environmental conditions, but understanding the complexities of hybrid interactions with N rate and plant density will require much more work.