Evaluation of the Crop Water Stress Index as an Indicator for the Diagnosis of Grapevine Water Deficiency in Greenhouses

Precise irrigation management of grapevines in greenhouses requires a reliable method to easily quantify and monitor the grapevine water status to enable effective manipulation of the water stress of the plants. This study evaluated the applicability of crop water stress index (CWSI) based on the leaf temperature for diagnosing the grapevine water status. The experiment was conducted at Yuhe Farm (northwest China), with drip-irrigated grapevines under three irrigation treatments. Meteorological factors, soil moisture contents, leaf temperature, growth indicators including canopy coverage and fruit diameter, and physiological indicators including SPAD (relative chlorophyll content), stem water potential (phi s), stomatal conductance (g(s)), and transpiration rate (E) were studied during the growing season. The results show that the relationship between the leaf-air temperature difference (T-c-T-a) and the plant water status indicators (phi s, g(s), E) were significant (P < 0.05), and the relationship between g(s), E and T-c-T-a was the closest, with R-2 values ranging from 0.530-0.604 and from 0.545-0.623, respectively. CWSI values are more easily observed on sunny days, and it was determined that 14:00 BJS is the best observation time for the CWSI value under different non-water-stressed baselines. There is a reliable linear correlation between the CWSI value and the soil moisture at 0-40 cm (P < 0.05), which could provide a reference when using the CWSI to diagnose the water status of plants. Compared with the T-c-T-a value, the CWSI could more accurately monitor the plant water status, and above the considered indictors, g(s) has the greatest correlation with the CWSI.