Corn yield and shifts among corn quality constituents following application of different nitrogen fertilizer sources at several times during corn development

Corn plants grown under higher nitrogen (N) fertility have a higher grain protein concentration. However, it is not known whether the increased protein concentration is due to decreases in the concentration of nonstructural carbohydrate (energy content approximately equal to protein), lipid (energy content approximately 2.5 times that of protein), or other components (largely structural carbohydrate). An increase in protein concentration that results in a decrease in lipid concentration will decrease the energy content per unit dry weight of grain corn. A 3-year field experiment was conducted at four locations in Eastern Canada to evaluate the effects of N fertilizer source, application rate, and application time on the yield and quality of corn (Zea mays L.). Ammonium nitrate, urea, and calcium ammonium nitrate were applied at rates of 90 and 180 kg N/ha. The N fertilizer was applied as a) a single application: entirely pre-plant incorporated (PPI), b) in two applications: 1/2 PPI and 1/2 when corn plants were 15 cm tall, and c) in three applications: 1/3 PPI, 1/3 when plants were 15 cm tall, and 1/3 when plants were 90 cm tall. Corn grain protein concentration increased with N application in all the location-years; the average increase was 8.40%, with the application of N fertilizers as compared to the control. The protein content (mg) per kernel increased with N application in half the cases. Both corn grain protein concentration and content were not different among the three N application timings in most location-years. The lipid concentration of the grain was not affected by any N treatment indicating that the increase in protein concentration did not decrease in energy concentration. However, the concentration of remaining grain components (largely fibre and cellulose) decreased as the protein concentration increased, so that high N fertility may have increased both protein and energy concentrations of the grain. Grain yield increased with increasing N fertilizer application rate, and it was generally not significantly affected by the number of the N application times. Neither corn yield nor corn quality were affected by the different N sources.