Whole-Plant Tissue Nitrogen Content Measurement Using Image Analyses in Floriculture Crops

Research on image analysis techniques for estimating plant N status in floriculture is limited. We subjected poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) cultivars to five nitrogen concentration treatments for 45 days and captured grayscale images of plants briefly exposed to 450, 625, 660, and 870 nm of light using a multispectral image station. Images were processed to calculate normalized reflectance ratios, including R870/450, R870/625, and R870/660. Dried shoots were analyzed in a laboratory for whole-plant tissue N content (mg·g−1). Results indicated that whole-plant N content ranged from 21 to 44 mg·g−1 in different N treatments. Among the reflectance ratios, R870/625 showed higher correlation with whole-plant N content in different cultivars of poinsettia (0.72< r2 <0.78) compared to R870/450 and R870/660. Based on these results, we custom-built a low-cost image sensor that can be remotely controlled to capture red (625 nm) and near infrared (870 nm) images of plants and transfer images to a cloud storage for processing. The normalized reflectance ratio measured by the image sensor was linearly related to the whole-plant N content (r2=0.84) and more accurate than soil plant analysis development (SPAD) measurements at predicting plant N status. These results indicate that image analysis in general and images captured by low-cost image sensors can be used for estimation of plant N status in floriculture. Index words: Chlorophyll, poinsettia, red light reflectance, plant segmentation. Chemicals used in this study: Water soluble 15-5-15 Cal Mg. Species used in this study: Poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch, cultivars ‘Christmas Beauty Marble', ‘Christmas Tradition', ‘Christmas Glory White', and ‘Wintersun White').