While increasing plant density is a promising strategy for higher maize yields, high plant populations must be managed to lessen plant competition. Our objectives were to determine how to properly manage increasing plant populations through row arrangement and plant nutrition.

A commercial hybrid (DKC 61-21 SSTX) was grown in two locations (Fairholme Farms near Lewisville, IN and Champaign-Urbana, IL) in 2010. Row configurations consisted of either single rows (0.76 m) or twin rows (0.57 m inter and 0.19 m intra) with six different plant density levels (86,000, 99,000, 111,000, 124,000, 136,000 and 161,000 plants ha^-1), while the fertility level was altered with four rates of MESZ (0, 56, 112, or 168 kg P₂O₅ ha^-1). Treatments were arranged as complete factorial (2x4x6) in a randomized complete block experimental design with four replications.

In 2010, increased plant density had a clear negative effect on grain yield, which was probably related to unusually warm weather during grain fill. The lowest plant density levels consistently had the highest grain yields, and there was a downward trend in grain yield that coincided with increasing plant density. The lower plant densities had larger individual kernel weight as well as increased kernel number per area when compared to the higher plant densities. There was no effect of row configuration (main effect of single vs. twin rows) on grain yield, but there was a significant row configuration by plant density interaction indicating that the twin row planting pattern was significantly worse than single rows at higher levels of plant density. Conversely, addition of the MESZ fertilizer increased yield at all plant populations and for both row arrangements, and this effect was observed visually as more vigorous early season plant growth.We expect that the effect of optimized fertility at higher plant densities will be magnified in environments that respond to increased plant density.

Although adverse weather during grain fill limited the response to plant population or row configuration in 2010, the increase in grain yield from the added fertility suggests that plant nutrition is an important component in managing a higher plant population for higher yields.