Corn response to population is continuously changing with seeding rates increasing about 280 plants/acre/year according to the National Agricultural Statistics Service (2010). Plant populations in Ohio have increased 16% in the past 10 years (56% since the early 1970s). According to NASS, plant population for corn in Ohio averaged 28,200 plants/acre in 2010, which is lower than most Corn Belt states (e.g., Minnesota, 29,900; Iowa, 29,950; Illinois, 29,650; Indiana, 28,350 plants/acre).

Research has demonstrated that the superiority of modern hybrids is fully expressed only at higher plant populations (Duvick, 2005). When hybrids of different eras (from the 1930s through 2001) were planted at a very low population (4,000 plants/acre – a “low-stress” environment), there was little to no difference in the yields of hybrids from different eras. However, when established at a higher plant population (32,000 plants/acre) more typical of that required to maximize yields in recent years, hybrids exhibited progressively higher yields with each era of genetic improvement. The genetic improvements that have facilitated the positive interaction between hybrids and increasing seeding rates include increased yield stability across a range of environmental conditions, greater tolerance to drought (and higher plant populations), enhanced stalk and root strength, and resistance to diseases and insects.

The distribution of corn acreage with varying plant populations at harvest indicates major differences in seeding rates used for corn production in Ohio and greater adoption of higher seeding rates by some corn growers in recent years. Final stands on nearly 40% of the state’s corn acreage was 30,000 plants/acre or higher in 2010. Four years ago, final stands were 30,000 plants/acre or higher on only 14% of the corn acreage.

Most corn agronomists recommend adjusting seeding rates by using the yield potential of a site as a major criterion for determining the appropriate plant population. Seed companies recommend final stands as high as 35,000-36,000 plants/acre for some hybrids in high-yield environments. Average seeding rates of hybrids entered in the Ohio Corn Performance Test have increased from about 25,000 seeds/acre in the early 1970s to over 35,000 seeds/acre in 2010 (with final stands ranging from about 23,000 to 33,000).  Ohio Corn Performance Test sites generally represent production environments with high yield potential.