Evaluation of Five Methods to Measure Normalized Difference Vegetation Index (NDVI) in Apple and Citrus

Normalized Difference Vegetation Index (NDVI) is a common remote sensing calculation used to assess green biomass in addition to nutrient, pest, and water stress. The approach used in NDVI has potential for a broader use of remote sensing of plant physiological status. The purpose of the study was to evaluate techniques to that utilize combined near-infrared (NIR) and visible detection by low cost web cameras in comparison with a dedicated NDVI sensor and direct measurement of red-green-blue (RGB) and NIR bands to calculate NDVI and identify water stress. Established techniques as well as new techniques for NDVI computation from cameras were evaluated and compared to soil plant analysis development (SPAD) chlorophyll meter values to assess the accuracy of NDVI for predicting plant stress in apple and citrus. NDVI is a useful tool when evaluating long-term crop changes such as pest damage, chronic water shortage, and nutrient deficiencies that affect chlorophyll but NDVI is not useful for acute stresses such as an irrigation pump failure or plugged irrigation lines that have an effect within days.