Site-specific study of corn protein, oil, and extractable starch variability using nit spectroscopy

To determine variability in corn protein, oil, starch, and extractable starch, near-infrared transmission (NIT) was used on samples from 640 sub plots that were planted with two varieties at four population levels, five nitrogen levels, and two nitrogen application methods. A GLM analyses of variance indicated NIT protein content increased significantly with increases in nitrogen rate and changes in method of nitrogen application. Protein ranged from 5.7% to 11.0% over all plots and treatments. The highest protein content occurred on plots receiving 202 kg N/ha; while the lowest occurred on plots receiving no nitrogen. Oil percentages did not vary significantly with nitrogen rate and they ranged from 2.2% to 4.3%. Starch content and extractable starch decreased significantly as nitrogen rate increased. Extractable starch ranged from 63.4% to 72.1%. The highest extractable starch level of 72.1% occurred on the plots with no nitrogen application; while the lowest extractable starch occurred on plots receiving 202 kg N/ha. Starch content ranged from 72.0% to 76.1%. Soil Plant Analysis Development (SPAD) readings increased significantly with nitrogen rate, application method, and population increases. They ranged from a mean of 44.5 at the lowest nitrogen level to 52.2 at the highest nitrogen level. Yield increased from a mean of l0.5 tonnes/ha at the 0 nitrogen level to 11.5 tonnes/ha at the 202 kg N/ha level. Extractable starch had a negative correlation (R² = -0.76)with protein and a positive correlation (R² = 0.65) with starch content.