Part 1, Section 4: Corn
Corn
ESTABLISHMENT
Plant populations
The optimum plant population range for corn varies depending on the yield potential of the soil, the hybrid, and the intended use of the crop. For many Pennsylvania soils, a harvest population of 26,000 to 28,000 is necessary to achieve maximum economic grain yields. On the best soils, where yields of 175 bushels/acre and higher are common, plant populations of 30,000 plants per acre are needed to maximize grain yields. On droughty or poorly drained soils, with grain yield potentials in the 100 bu/A category (see Table 1.1-1, Selected properties of Pennsylvania soils), optimum plant populations are lower, in the 24,000 to 26,000 range.
Hybrids vary in their tolerance of high populations, and some may experience some lodging at the upper end of these ranges. Consequently, you should review the seed company plant population recommendations for each hybrid and adjust accordingly. Also consider populations at the lower end of these ranges in fields where gray leaf spot is common and there is an increased risk of lodging.
For silage production, higher plant populations are warranted. Generally, optimum populations appear to be about 2,000 to 4,000 plants per acre higher for silage than grain. Thus, on most soils, 28,000 to 32,000 plants per acre appears to optimize both yield and forage quality. Higher plant populations can increase yields, but the energy content of the forage appears to decrease slightly. In a recent two-year test conducted at Rock Springs, increasing plant populations from 30,000 to 36,000 plants per acre increased yield by 0.7 tons/acre (35 percent DM) and decreased whole plant digestibility by 0.7 percentage units. The forage quality response to increased plant populations may also vary with hybrids, particularly with leafy hybrids, so be sure to review the seed company planting recommendation for hybrids grown for silage as well.