Use of low-cost RGB images to estimate nitrogen, chlorophyll, and leaf area status in basil ‘Nufar’

Abstract

Nitrogen is a critical nutrient for basil (Ocimum basilicum L.), significantly influencing chlorophyll synthesis, leaf area development, and plant productivity. Traditional nitrogen assessment methods are destructive, time-consuming, and costly, limiting their practicality. Low-cost red-green-blue (RGB) imaging offers a promising alternative for the rapid, nondestructive estimation of plant nutritional status; however, its applicability in aromatic herbs like basil remains underexplored. This study evaluated using RGB imaging to estimate leaf area, nitrogen, and chlorophyll status in basil ‘Nufar’ as a tool for precision nutrient management. Using the Steiner nutrient solution, the basil plants were grown in a greenhouse under five nitrogen levels (0, 4, 8, 12, and 16 [mEq∙L−1] of NO3−NO3−). Weekly RGB images were acquired and processed through photogrammetric restitution to generate scaled orthomosaics. Seventeen spectral vegetation indices were obtained and correlated with reference measurements of nitrogen, chlorophyll, and leaf area by regression analysis. Results showed that a nitrogen level of 16 mEq∙L−1 NO3− significantly enhanced plant growth, development, and green coloration. Among the indices evaluated, the Normalized Green-Red Difference Index (NGRDI), Red Index (RI), and Color Index of Vegetation Extraction (CIVE) exhibited the strongest correlations with nitrogen concentration (r = 0.92–0.93), chlorophyll concentration (r = 0.94–0.97), and leaf area (r = 0.93–0.97). These findings confirm that low-cost RGB imaging provides an accurate and efficient method for monitoring nitrogen status, chlorophyll content, and leaf area in basil ‘Nufar.’ This approach offers a valuable tool for optimizing nutrient management and yield prediction in this economically important medicinal and aromatic species.

Plant phenotyping relevance

低コストRGB画像とフォトグラメトリによる植物栄養状態・葉面積・クロロフィル推定が研究の中心であり、画像取得・処理と指標の技術評価を実施している。

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