N Management for High Population Corn Production in Wide and Narrow Rows.

Optimum N timing and rate were determined for high population density corn (Zea mays L.) based on early-season plant development, yield components, and grain yields at 13 sites over a three-year period in North Carolina, USA. Corn yield response was used to assess optimum fertilization strategy, and early season N uptake and yield component responses were used to assess the likely timing of any N stresses. The 19% grain yield increase in response to application of N fertilizer could be attributed to changes in ear yield components: kernels per row increased by 17%, mean kernel weight increased by 8%, and rows per ear increased by 3%. Highest grain yields were found with narrow rows and sidedress N applications. For these high population corn production systems, it appears critical to maintain sufficient N supply later in the season to contribute to the formation of the later-determined ear yield components. All of our management treatments included a banded starter fertilizer that supplied 7 kg N ha^-1 near the crop row, which appeared sufficient to support most of the early season plant N uptake. A minor increase in aboveground N accumulation, from 9 kg ha^-1 to 10 kg ha^-1 (by V5-7),  was possible if an additional 224 kg ha^-1 was applied at planting. In order to insure adequate late-season N for field corn, later N application timing and/or the application of more persistent N sources may be needed. Response to N fertilization varied substantially across experimental sites and application timings, with significant yield responses to N at all site years except N applied at planting at one site. Efficiency of N use was quantified as an N application factor with a mean of 15 kg N Mg^-1 grain, with observed values ranging from 3 to 35 kg N Mg^-1 grain.