Crop reflectance indices for mapping water stress in greenhouse grown bell pepper

Early detection of plant water status is essential to optimize crop water use, and to implement water savings methods such as precision irrigation. This study investigated the potential of using crop reflectance indices to detect water stress, in order to improve irrigation of bell pepper (Capsicum annum L.), grown under greenhouse conditions. Spectral data were acquired from bell pepper plants, with five different irrigation regimes namely 100, 80, 60, 40, and 20% of plant available water, in a completely randomized design. Plant stress parameters including stomata] conductance (G(s)), canopy temperature (Tc), relative water content (RWC), yield, and volumetric soil moisture content (SMC) were concurrently measured with spectral data acquisition from the plants throughout the growing season. Various reflectance indices including Normalized Difference Vegetation Index (NDVI), Renormalized Difference Vegetation Index (RDVI), Optimized Soil Adjusted Vegetation Index (OSAVI), Photochemical Reflectance Index centered at 570 nm (PRI570), Photochemical Reflectance Index centered at 553 nm (PRI553), normalized PRI (PRInorm), Water Index (WI), and WI/NDVI were obtained from the spectral data. The relationships between these crop reflectance indices and the water stress indicators were statistically examined at the five irrigation levels. The results revealed that PRI553, WI, RDVI, PRInorm, and WI/NDVI were the most useful indices for detecting water stress in bell pepper plants. The findings of this study show promise of using a proximal method for assessing water stress and to improve water management of high value vegetable crops grown under greenhouse conditions.