Near‐field fluorescence measurements for nutrient deficiencies detection on potatoes (Solanum tuberosum L.): effects of the angle of view

In this study we evaluated the impact of various measurement angles on the potential of nutrient deficiency detection using UV‐induced fluorescence. Potato plants (Solanum tuberosum L., cv. Superior) were grown in a greenhouse and three nutrient deficiencies were induced (K, Mg, and N). Leaf fluorescence measurements were detected at the four emission bands (440, 520, 690, and 740 nm) under two different excitation wavelengths (360 and 436 nm) by which the most commonly used fluorescence ratios were computed. Fluorescence measurements were taken at three different angles by inclining the plant in front of the fluorometer. RGB pictures of each plant scene were taken and a veins/lamina ratio (V/L) was computed. Results show that nitrogen deficiency was more easily detected when the fluorometer was aimed at older leaves (angle of 45°). Moreover, the veins/lamina ratio has an impact on the detection potential of fluorescence. Following our results, it seems that a high V/L improves the detection of K‐ and Mg‐deficiency whereas a low V/L improves the detection of N‐deficiency.