SPECTRAL IMAGING IN THE EVALUATION OF THE CHLOROPHYLL CONTENT IN WHEAT

Abstract

The objective of our research was to evaluate the nutritional status expressed through the chlorophyll content in wheat crops, by using the analysis of the digital images taken in the visible spectrum. The study is based on observations of different colors expressed by plants in the visible spectrum, following a different nutritional status. These data about colors were associated and correlated with the chlorophyll content. The biologic material was represented by Alex variety of wheat (Triticum aestivum ssp. Vulgare). The nutritional stress which generated the variation in the chlorophyll content was induced by controlled nitrogen fertilization, in doses between 0 - 200 kg active substance ha -1 with four levels of PK 0 - 150 kg active substance ha -1 . Chlorophyll content of wheat plants was determined with a portable chlorophyll meter (Konica Minolta SPAD 502 Plus) to measure absorbance leaves red and near infrared region. Determination of chlorophyll was done in the same time to capture digital images. Capturing digital images made with a Nikon D80 at uniform parameters for all variants. The digital images, captured in the visible spectrum, were analyzed from the point of view of their color spectrum by nonlinear perceptual representation systems RGB, HSB and HSL. Chlorophyll content ranged from 40.26 ± 1.36 (SPAD units) from control variant (P0K0N0) and 55.57 ± 0.55 (SPAD units) at P150K150N200 variant. After the correlative analysis of the numerical values resulted on color channels (H,S,B and H,S,L) and chlorophyll, we obtained correlations with high significance level (very significantly negative correlation between the chlorophyll content and color channel BHSB, r = -0.930). Multi-parameter analysis of the variables, accomplished through cluster analysis and data grouping based on Euclidean distances, places the experimental variants according to the fertilization level. Their disposition is also correlated with the chlorophyll content and HSB and HSL values resulted from tests carried out and from the data stored in digital images.

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