Thermal- and RGB Imaging as Potential Tools for Assessing Chlorophyll and Nutritional Performance of Pepper (Capsicum annum)

Abstract

Nutrient management requires traditional soil and plant analysis, which is time-consuming, costly, and requires effort. Therefore, a lot of efforts have been directed toward developing novel approaches for estimating plants’ status. Our objective was to evaluate the potential of thermal and RGB imaging to estimate Chlorophyll levels and some essential nutrients in the pepper plant (Capsicum annum). Forty plants were randomly selected and marked for subsequent imaging. Thermal and RGB sensor cameras have been used for remotely sensed image acquisition of the studied plants. Chlorophyll was measured by SPAD then Plants were analyzed for determination chlorophyll, Nitrogen, Phosphorus, Potassium, and sulfur contents. The correlation between the measured/observed values and data of thermal and RGB images was calculated, as well as seven vegetation indices. The results showed that Chlorophyll b, and Chlorophyll measured by SPAD significantly correlated with the blue band of RGB images (r=0.625 and 0.709), respectively. To assess the Chlorophyll performance, excess blue, excess green, excess green-red, and excess red indices, and the Color Index of Vegetation (CIVE) were the best. In thermal imaging: band3 in capture 1 was the best to assess Chlorophyll. The more fitting band to assess Nitrogen, potassium and sulfur was band2 in capture2. The more detective indices to assess pepper nutrient content were excess blue, excess green, excess green red, and CIVE indices. The regression analysis revealed that a simple linear equation can be used to estimate the percentage of Nitrogen, sulfur, and potassium in plants using the excess green index (r = 0.9159, 0.8942, 0.8715, and 0,9117, respectively) and the red-blue ratio index (RBRI) could be used to estimate the percentage of P (r = 0.9098). Thermal and RGB imaging can be used as a tool for assessing some nutrients and Chlorophyll content in pepper plants.