Assessing the Reliability of Thermal and Optical Imaging Techniques for Detecting Crop Water Status under Different Nitrogen Levels

Abstract

Efficient management of irrigation water is fundamental in agriculture to reduce the environmental impacts and to increase the sustainability of crop production. The availability of adequate tools and methodologies to easily identify the crop water status in operating conditions is therefore crucial. This work aimed to assess the reliability of indices derived from imaging techniques-thermal indices (I g (stomatal conductance index) and CWSI (Crop Water Stress Index)) and optical indices (NDVI (Normalized Difference Vegetation Index) and PRI (Photochemical Reflectance Index))-as operational tools to detect the crop water status, regardless the eventual presence of nitrogen stress. In particular, two separate experiments were carried out in a greenhouse, on two spinach varieties (Verdi F1 and SV2157VB), with different microclimatic conditions and under different levels of water and nitrogen application. Statistical analysis based on ANOVA test was carried out to assess the independence of thermal and optical indices from the crop nitrogen status. These imaging indices were successively compared through correlation analysis with reference destructive and non-destructive measurements of crop water status (stomatal conductance, chlorophyll a fluorescence, and leaf and soil water content), and linear regression models of thermal and optical indices versus reference measurements were calibrated. All models were significant (Fisher p-value lower than 0.05), and the highest R 2 values (greater than 0.6) were found for the regression models between CWSI and the soil water content, NDVI and the leaf water content, and PRI and the stomatal conductance. Further analysis showed that imaging indices acquired by thermal cameras (especially CWSI) can be used as operational tools to detect the crop water status, since no dependence on plant nitrogen conditions was observed, even when the soil water depletion was very limited. Our results confirmed that imaging indices such as CWSI, NDVI and PRI can be used as operational tools to predict soil water status and to detect drought stress under different soil nitrogen conditions.

Plant Nutrient Dynamics in Stressful Environments: Needs Interfere with Burdens

“…Instabilities (e.g., caused by climatic factors or pests) should be detected as early as possible to initiate corrections in the nutrient supply or in other growth conditions. Sensitive detection systems for nutrient disorders in the field can facilitate this task, and are therefore, highly desirable [36].…”

Agronomic Basis and Strategies for Precision Water Management: A Review

“…This can be helpful in site-specific management of irrigation water, as well as weedicide, pesticide and other chemicals [106][107][108]. Various indices derived from thermal and multispectral images, such as crop water stress index (CWSI), perpendicular vegetation index (PVI), normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI), can predict soil or plant water status and drought stress as a basis for site-specific water management [109,110]. Use of digital infrared thermography to measure canopy temperature can help producers to detect early crop water stress and avoid yield declines as well as saving water with site-specific irrigation management and irrigation scheduling [111,112].…”

Latest Developments in Sustainable Water Management

“…Water stress can reduce and remove specific spectral properties of the crop through e.g. lowering of the red light absorbance [27]. Masseroni et al investigated the reliability of thermal and optical indices derived from imaging techniques for detecting the crop water status.…”