Quantification of water stress by infrared thermometry is routinely done on complete plant canopies to minimize the influence of viewed soil surface. When plants are small or widely spaced, canopies may not be complete. This study was conducted to determine if Crop Water Stress Index (CWSI) values computed from infrared thermometer measurements of single‐leaf temperatures of sunflower [ Helianthus annuus (L.) ‘Triumph 566DW’] were correlated with other measures of plant water stress. Plants were grown under an automated rainout shelter and subjected to four water treatments ranging from 0.0 to 100% replacement of evapotranspirational losses. The soil type is a Rago silt loam (fine, montmorillonitic, mesic Pachic Argiustoll). Statistically significant correlations were found between CWSI calculated from single‐leaf temperatures and stomatal conductance, CO 2 exchange rate, leaf water potential, transpiration rate, and percent available water in the active root zone. Calculating CWSI from single‐leaf temperatures measured with an infrared thermometer can provide a rapid means of assessing plant water status in incomplete canopies.
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Nielsen et al. (1989) studied this question.