There is considerable interest in increasing corn yields with modern hybrids at higher than normal planting densities and adequate nitrogen (N) rates. In 2013, two hybrids, DKC48-12 and DKC49-94, both having insect and herbicide-stacked technology and improved drought tolerance capabilities, were tested at two row spacings of 20 inches and 30 inches with three population densities of 30,000, 36,000 and 42,000 plants per acre.
Two N rates of 120 pounds per acre and 240 pounds per acre were applied. The yield response of the two hybrids to row spacings and population rates was discussed in "Corn yield enhancement through planting densities and nitrogen management – Part 1. In this article, the yield response to the third variable, the N rate, is discussed. Most of the N was applied as a sidedress injected using 28 percent liquid UAN on June 19, 2013.
Yield data from the two hybrids are summarized in Tables 1 and 2. Both hybrids produced highly significant yield increases at the high N compared to low N rate at all three populations. DKC48-12 had an average increase of 16 bushels per acre and DKCV49-94 had an average increase of 10 bushels per acre.
The 2013 growing season was dominated by excessive rainfall in April and June (Table 3) compared to an average year, delaying planting until May 20 and drowning out portions of the field in June. About one-third of June rainfall occurred after the June 19 N sidedress application. The wet and soggy conditions may have contributed to N losses due to denitrification and leaching.
The end of season cornstalk nitrate-N test was conducted on the two N rates (Table 4). The stalk nitrate-N level in the low N treatment was below the critical range of 700-2,000 ppm, indicating a potential N deficiency during the season. This N shortage may have reduced corn yield. The stalk nitrate-N level in the high N treatment was slightly above 2,000 ppm. It is possible, therefore, that the optimum N rate was between 120 and 240 pounds per acre.
This project was funded by Project GREEEN. I wish to thank the Dekalb/Asgrow staff at the Mason Technology Center for their collaboration with Michigan State University Extension and providing seed, equipment, and labor for this study.