Study of Irrigation and Nitrogen Rate Impact on Corn Yield and Spectral Reflectance in Alabama.

High food demand is forcing farmers to increase yield. High rates of inputs, water and nitrogen (N), are then used as yield increase strategies. The objective of this study was to investigate the effects of irrigation and N application on yield and corn spectral reflectance at middle and late growth stages to determine in-season N rates and losses. This experiment is been conducted in Alabama using a split-plot design. Five nitrogen (N) treatments of ammonium nitrate (UAN, 28-0-0) were used as the subplots and 3 levels of irrigation (100, 75, and 50% of the field capacity) were used as the main plot. Two treatments received 2 applications (planting and V6) of 160 kg N ha^-1 and 214 kg N ha^-1 during the growing season and two treatments received 3 applications (planting, V6, and V12) of the same rates. When the application of N was split three times over the growing season and sufficient irrigation water was available, significant increase of grain yield was observed. In contrast, when 2/3 of the total N was applied at V6 and irrigation was limited, no yield differences was observed among N treatments. Strong correlation between grain yield and vegetation indexes such as normalized difference vegetation index (NDVI) and normalized difference vegetation red edge index (NDRE), and chlorophyll index red-edge (CI) was observed. Therefore, remote sensing seems a promising tool for assessing in season N deficiencies and in-season estimation of N application rates.