Sensitivity of Narrow‐Band and Broad‐Band Indices for Assessing Nitrogen Availability and Water Stress in an Annual Crop

We evaluated a suite of vegetation indices to detect treatment differences in nutrient and water availability in corn for areas larger and smaller than the ground sample diameter (GSD) from both a portable spectrometer and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The ANOVA results for a N trial showed that indices based on the chlorophyll red‐edge were more sensitive to differences in N treatment than those based on the visible and near infrared (NIR) regions only. Classifications of pixels for a spatial detection study using unfertilized strips with widths of 6 m, 12 m, 18 m, and 24 m were performed and scored as the percentage of correctly classified pixels. Generally, the indices using the red‐edge produced more accurate detections, although none of the indices could detect nutrient stress in the 6‐m strips based on 15‐m imagery. A water stress study was set up in another location of the same field by withholding irrigation water. While the indices based on the chlorophyll red‐edge outperformed others for N application detection, the visible and NIR indices differentiated water stress the best.