Carl R. Crozier1, Ronald J. Gehl2, Ronnie W. Heiniger1 and David H. Hardy3, (1)207 Research Station Road, North Carolina State University, Plymouth, NC (2)North Carolina State University, Mills River, NC (3)North Carolina Department of Agriculture, Raleigh, NC
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.