Plant Population Effects on the Morphology of Corn Hybrids in Different Relative Maturity Groups.

Advances in genetic selection and agronomic production are two major contributors to corn grain yield, but studying their interaction may provide further increases in grain yield. High plant populations may alter ear height, dominant ear shoot, and ear orientation at harvest differently for different hybrid maturities, which could affect harvestability. A field study was conducted from 2010-2014 in South Charleston and Hoytville, OH to investigate how plant population affects corn hybrids in different maturity groups. Depending on the year, five to nine corn hybrids ranging in relative maturity from 101 to 107 day were selected as short-season hybrids, and nine to 15 hybrids ranging in maturity from 108 to 116 day were selected as full-season hybrids. Hybrids were planted at five populations ranging from 44,000 to 124,000 plants ha^-1 each year. Plant height, ear height, and number of leaves above the ear were measured at R2. Ear orientation, stalk lodging, grain yield, moisture content, and test weight were measured at harvest. Both short- and full-season hybrids exhibited similar morphological responses to increasing plant population. Plant height and leaves above the ear was not affected by planting population, but ear height at 44,000 plants ha^-1 was 2.5 cm lower than at higher populations. At harvest, 46 and 53% of ears were upright for short- and full-season hybrids, respectively, at 44,000 plants ha^-1, and decreased by 20% as population increased. However, short-season hybrids compared to full-season hybrids were 12 cm shorter, exhibited ear heights 4 cm lower, and had fewer upright ears at harvest when compared to full-season hybrids across populations. Stalk lodging at harvest increased for both maturity groups with population, but full-season hybrids exhibited greater lodging across populations compared to short-season hybrids. Plant population did not alter grain moisture and test weight for either maturity group, but short-season hybrids exhibited 25 g kg^-1 lower grain moisture and 12.9 kg m^-3 greater test weight as compared to full-season hybrids. The only parameter with a significant population by maturity group interaction was grain yield. The agronomic optimum plant population for short-season hybrids was 96,000 plants ha^-1 to maximize yield (12.3 Mg ha^-1), but full-season hybrids produced maximum yield (12.6 Mg ha^-1) at 86,500 plants ha^-1. This research suggests that increasing population has a similar morphological effect on hybrids with different relative maturity. However, inherent differences in plant and ear height, and ear orientation at harvest may contribute to the differences observed in grain yield.