Iron, magnesium, nitrogen and potassium deficiency symptom discrimination by reflectance spectroscopy in grapevine leaves

This work aims at the identification and discrimination of mineral deficiency symptoms by reflectance spectroscopy. Vitis vinifera L. plants were subjected to 5 different hydroponic mineral nutrition: control and iron, magnesium, nitrogen and potassium deficiencies. Basal, young and apical leaves were studied. Spectra were collected along veins, in interveinal areas and in leaf margins. Reflectance spectroscopy appeared to be able to discriminate the mineral deficiencies, producing characteristic pigmentations and symptom distribution. These results appeared to be coherent with the physiological role of each nutrient. The most promising target in terms of leaf position and wavelengths of interest were identified for each condition. Mineral deficiencies also produced specific pigment distribution within the same plant, suggesting the possibility of symptom identifications also without the availability of well-fed control plants in field conditions. The reflectance spectral feature of the leaves could support the identification of mineral deficiencies in field conditions. These results could support further researches, including index development for symptom intensity quantifications and definition of threshold values for fertilization management. Due to the rapidity and low cost of the technique, future applications could support both technical requests and scientific researches.