Normalized Difference Vegetation Index (NDVI)
Plant stress, whether it be water, nutrient, heat, etc., detection can be difficult, especially during early stages. One indicator of plant stress is light absorption and reflectance. Since chlorophyll absorbs the red band of incoming radiation, the reflectance is relatively low due to the strong absorption of the light by
the plant pigments. The high reflectance in the near infrared band is caused by the cellular structure of the plant leaves, particularly the spongy mesophyll leaf structure. When plants are under stress, red band reflectance increases due to reduced chlorophyll absorption. Near infrared band reflectance
decreases due to cell structure breakdown. The normalized difference vegetation index (NDVI) is a unit of measure designed to factor both red and near infrared reflectance. NDVI measurements can range from -1 to 1, with
higher values indicating greater plant health. Use NDVI measurements to schedule nitrogen applications by keeping a high nitrogen reference strip.
