Planning the Water requirement supply of Pasture shrubs under different Irrigation systems using plant Water Stress Index

The crop water stress index based on canopy–air temperature differences (CWSIdT) is an appropriate index for monitoring the water status of croplands but is rarely used to evaluate the water status of forest ecosystems. However, CWSIdT is rarely used in forest ecosystems. Investigating the possibility of using the crop water stress index (CWSI) for planning the irrigation of four species of pasture trees, Prosopis cineraria (T1), Conocarpus (T2), Albezia lebbek (T3) and Ziziphus (T4), under four methods of surface irrigation, bubbler, pitcher, and waterboxx system, was selected. This research was conducted in the year 2021 in the experimental farm of the Faculty of Water and Environmental Engineering of Shahid Chamran University of Ahvaz and lasted for 9 months. The experiment was conducted as a factorial in the form of a randomized complete block design with 3 replications. The crown temperature, actual evaporation and transpiration and meteorological factors of the field were continuously and simultaneously measured during the period from the beginning of April to the end of December. Infrared thermometers was used to measure crown temperature and vapor pressure deficiency values for different irrigation treatments. The results showed that under well-watered conditions, canopy-air temperature difference and canopy surface transpiration rate are both controlled by the net radiation received by the canopy surface The highest and lowest calculated CWSI values were related to waterboxx and Pitcher irrigation with values of 1.01 and 0.81, respectively, which were related to Ziziphus and Konocarpus trees. Statistical analysis showed that the effect of irrigation method on plant water stress index values in spring and autumn seasons was significant at the level of 5% and the average values of plant water stress index increased with water consumption reductions of 87 and 59% in waterbox and pitcher irrigation systems, respectively. However, there was no significant difference observed in the summer season. Also, the effect of tree type on the CWSIdT index during the period was important at a 1% level. In addition, the difference in vegetation and air temperature were used as a determining factor to determine irrigation time, which can be used to estimate pasture tree water stress.