A two-year (2010-2011) field experiment was undertaken to examine the effect of nitrogen (N) rate (0, 100, 150, and 200 kg N ha-1) and N source (urea, calcium ammonium nitrate; ammonium sulphate) on canopy reflectance, chlorophyll pigments, photosynthesis, yield, grain quality, and N-use efficiency in corn. However, the physiological observations were made only in 2011. We found that stover biomass was unaffected by higher N rate beyond 150 kg N ha-1 in both years. Higher N rates did not provide a yield advantage as compared to 150 kg N ha-1 in 2010, but the highest grain yield was produced with 200 kg N ha-1 in 2011. The higher grain yield by N application was attributed to a greater kernel size in both years. Corn stover [N] was found to increase with increasing N rates in both years. Kernel [N] only responded to the high N rate in 2010. There was no change in the kernel density as affected by N rate in both years. An increased N addition resulted in a decrease in both N-uptake efficiency and agronomic-N use efficiency in both years. There was an inconsistent effect of N source on yield and N use efficiency indices in the corn over two years.
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Vol. 96 • No. 3