Phenotypic Response of Corn Hybrids and Maturity Groups to Plant Populations.

Grain yield potential of corn hybrids has increased dramatically over the last 50 years due to improvements in breeding techniques and hybrid development.  Many growers have begun increasing plant populations in efforts to maximize corn grain yield per hectare.  However, increasing plant populations may affect plant characteristics such as ear orientation and stalk strength.  A field study was designed to investigate how plant population may affect plant characteristics of different corn hybrids and maturity groups.  In 2010, the study was conducted at South Charleston and Hoytville, OH.  The study was repeated in 2011 with an additional site at Wooster, OH.  Each year, five corn hybrids ranging in relative maturity from 102 to 107 day were selected as early-maturing hybrids, and ten hybrids ranging in maturity from 108 to 114 day were selected as late-maturing hybrids.  Hybrids were planted at 44,000, 59,000, 74,000, 89,000 and 104,000 plants ha^-1 in 2010 and 44,000, 64,000, 84,000, 104,000, and 124,000 plants ha^-1 in 2011.  Plots were 8 m in length and consisted of four rows of corn at 0.76 m spacing.  The study was conducted with three replications per site as a split-plot randomized complete block, with whole-plot factor of population and sub-plot factor of hybrid.  Plant height, ear height, ear orientation at maturity, and lodging at maturity were measured prior to harvest.  Plots were harvested for grain yield and moisture content.  Means were separated using contrast statements and significance was determined at α=0.05.  Plant height was not affected by planting population for early-maturing hybrids in both years and late-maturing hybrids in 2010.  Late-maturing hybrid height decreased by 8 cm with population increases in 2011.  Additionally, late-maturing hybrids were 8 to 13 cm taller than early-maturing hybrids in both years regardless of population.  Ear height was similar for maturity groups in 2010, but ears were 8 cm higher in the late-maturing hybrids at 44,000 and 84,000 plants ha^-1 in 2011.  In both years, plants at the highest populations had the lowest percentage of erect ears regardless of maturity.  Plants at the lowest population had the greatest percentage of erect ears in the early-maturing hybrids in both years and the late-maturing hybrids in 2011.  Strong winds associated with thunderstorms in mid-July of 2011 caused root lodging, which increased with plant population.  In 2010, yields were similar between maturity groups at each population, and the maximum yield was obtained from 44,000 to 104,000 plants ha^-1.  In 2011, maximum yield was observed between 84,000 and 104,000 plants ha^-1.  Late-maturing hybrids had a 625 to 1000 kg ha^-1 yield advantage at 44,000 and 64,000 plants ha^-1 populations, but at 124,000 plants ha^-1 the early-maturing hybrids exhibited a 930 kg ha^-1 yield advantage over the late-maturing hybrids.  Grain moisture was consistently 1.5 to 2.0% greater in late-maturing hybrids compared to early-maturing hybrids, but was not affected by population in either group.  This research suggests that ear orientation at maturity was affected by population, which may be due to deterioration of shank strength at higher populations.  Root and stalk lodging were increased with greater population across hybrid maturities.  Low yields in 2011 at 124,000 plants ha^-1 may have been a result of greater root and stalk lodging, and ear orientation.