Irrigated Maize Response to Nitrogen and Populations.

Modern maize hybrids are more efficient at nitrogen uptake and better able to withstand stresses such as high population densities. Thus, it is hypothesized that higher maize populations in narrow rows require additional nitrogen to achieve higher yields. To test this, nitrogen rates of 196, 252, 308, 364 Kg N ha^-1 were applied to irrigated maize populations of 74, 99, 124, 148 thousand seeds ha^-1 at three locations in Kentucky in 38-cm rows. Measurements were collected through the season to determine the impact of plant density and nitrogen rate on plant nutrient concentrations, yield components and seed yield. A cost comparison analysis calculated the most economical nitrogen rate and population for each location. The first year of data indicated ear leaf nitrogen concentration was adequate at all sites at R1 stage, but higher populations had visible nitrogen deficiency closer to dominant ear leaves at R3 stage. Kernel number and kernel mass decreased with higher populations and nutrient concentration in maize fodder indicated potassium deficiency at one location. At a second site there was a linear correlation between higher plant populations and higher yield. The highest nitrogen rate did not correspond to the highest yield at any site suggesting that too much nitrogen could decrease nitrogen use efficiency. All three sites varied with the most economical population and nitrogen rate, but ranged from 99-148 thousand seeds ha^-1 and 252-308 Kg N ha^-1. The first year of data indicated that maximizing profit in irrigated maize with appropriate nitrogen rates and plant populations is variable depending on location. A second year of data has been collected in the same region of Kentucky.