Monitoring water status in apple trees using a sensitive morning crop water stress index*

Abstract

The crop water stress index (CWSI) has shown to be a good indicator of water status in fruit trees. Conventional CWSI measured over solar noon is widely used to monitor plant water status. This study compared the theoretical CWSI averaged over morning hours, CWSImo, and over solar noon hours, CWSImd, of apple trees. This study also assessed their sensitivity to the changes in soil water status (soil water deficit [SWD, %] and soil water potential [SWP, kPa]) at different root zone depths. Four different types of commercial and experimental apple orchards with different characteristics growing under semi‐arid conditions in Washington State, United States, were chosen to assess CWSImo against CWSImd sensitivity to soil water status. In some of these locations, soil water status ranged from fully watered to severely stressed (low water deficit to high water deficit). Ground‐based thermal and microclimate measurements were recorded continuously at 10‐s intervals and acquired for the 15‐min average on a daily basis throughout the study period. The linear relationship between SWD and CWSImo at the effective root zone depth (average of 0–150 mm and 0–460 mm) resulted in a slightly higher correlation (R2 = 0.42–0.64, p < .001) compared to the traditional CWSImd (R2 = 0.32–0.60, p < 0.001). The correlation between CWSImo and SWP (R2 = 0.38–0.69, p < 0.001) was found to be larger than the correlation between CWSImo and SWD, while SWP was less correlated with CWSImd (R2 = 0.33–0.55, p < 0.001). Interestingly, a better relationship between soil water status and both CWSImo and CWSImd was observed using a nadir view orientation thermal measurement. The CWSImo showed higher sensitivity to SWP than SWD.

Combining thermal imaging and soil water content sensors to assess tree water status in pear trees

“…The values of CWSI calculated in this study were similar to those reported by Egea et al. (2017) in olive trees under severe water stress but lower than those reported in apple trees under no water stress by Mohamed et al. (2021) .…”

“…(2021) . The difference in the values reported by Mohamed et al. (2021) under similar environmental conditions might be attributed to the calculation of the NWSB, as that study used an approach based on environmental conditions which might overestimate their calculation of the CWSI compared to when non-stressed leaves are directly measured.…”

Continuous Plant-Based and Remote Sensing for Determination of Fruit Tree Water Status

“…In practice, CWSI from remote sensing has proved useful for estimating PWS in terms of both water potential (Ψ stem and Ψ leaf ) and gas exchange (g s ) in woody fruit crops. Strong correlations have been shown in multiple crops, such as grapevine [105,238,247], olive [231,[248][249][250], almond [251], plum [243], peach [237,245,252], apple [253], cherry [223], pear [227], and citrus [228,254,255], among others. In 2023, Mortazavi et al developed a predictive model for determining the Ψ stem in almond and pistachio using vegetation indices obtained from aerial images through a machine learning approach [256].…”