CORN YIELD AND SHIFTS AMONG CORN QUALITY CONSTITUENTS FOLLOWING APPLICATION OF DIFFERENT NITROGEN-FERTILIZER SOURCES AT SEVERAL TIMES DURING CORN DEVELOPMENT

Com plants grown under higher nitrogen (N) fertility have a higher gra in protein concentration. However, it is not known whether the increas ed protein concentration is due to decreases in the concentration of n onstructural carbohydrate (energy content approximately equal to prote in), lipid (energy content approximately 2.5 times that of protein), o r other components (largely structural carbohydrate). An increase in p rotein concentration that results in a decrease in lipid concentration will decrease the energy content per unit dry weight of grain com. A 3-year field experiment was conducted at four locations in Eastern Can ada to evaluate the effects of N fertilizer source, application rate, and application time on the yield and quality of corn (Zea mays L.). A mmonium nitrate, urea, and calcium ammonium nitrate were applied at ra tes 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 applica tions: 1/2 PPI and 1/2 when com plants were 15 cm tall, and c) in thre e applications: 1/3 PPI, 1/3 when plants were 15 cm tall, and 1/3 when plants were 90 cm tall. Com grain protein concentration increased wit h 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 h alf the cases. Both corn grain protein concentration and content were not different among the three N application timings in most location-y ears. The lipid concentration of the grain was not affected by any N t reatment indicating that the increase in protein concentration did not decrease in energy concentration. However, the concentration of remai ning grain components (largely fibre and cellulose) decreased as the p rotein concentration increased, so that high N fertility may have incr eased both protein and energy concentrations of the grain. Grain yield increased with increasing N fertilizer application rate, and it was g enerally not significantly affected by the number of the N application times. Neither com yield nor corn quality were affected by the differ ent N sources.