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

Victor Blanco; Noah Willsea; Thiago Campbell; Orlando Howe; Lee Kalcsits

doi:10.3389/fpls.2023.1197437

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

Front Plant Sci. 2023 Jun 6:14:1197437. doi: 10.3389/fpls.2023.1197437. eCollection 2023.

Authors

Victor Blanco^{1

2}, Noah Willsea^{1

2}, Thiago Campbell^{1

2}, Orlando Howe^{1

2}, Lee Kalcsits^{1

2}

Affiliations

¹ Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA, United States.
² Department of Horticulture, Washington State University, Pullman, WA, United States.

Abstract

Volumetric soil water content is commonly used for irrigation management in fruit trees. By integrating direct information on tree water status into measurements of soil water content, we can improve detection of water stress and irrigation scheduling. Thermal-based indicators can be an alternative to traditional measurements of midday stem water potential and stomatal conductance for irrigation management of pear trees (Pyrus communis L.). These indicators are easy, quick, and cost-effective. The soil and tree water status of two cultivars of pear trees 'D'Anjou' and 'Bartlett' submitted to regulated deficit irrigation was measured regularly in a pear orchard in Rock Island, WA (USA) for two seasons, 2021 and 2022. These assessments were compared to the canopy temperature (Tc), the difference between the canopy and air temperature (Tc-Ta) and the crop water stress index (CWSI). Trees under deficit irrigation had lower midday stem water potential and stomatal conductance but higher Tc, Tc-Ta, and CWSI. Tc was not a robust method to assess tree water status since it was strongly related to air temperature (R = 0.99). However, Tc-Ta and CWSI were greater than 0°C or 0.5, respectively, and were less dependent on the environmental conditions when trees were under water deficits (midday stem water potential values< -1.2 MPa). Moreover, values of Tc-Ta = 2°C and CWSI = 0.8 occurred when midday stem water potential was close to -1.5 MPa and stomatal conductance was lower than 200 mmol m^-2s^-1. Soil water content (SWC) was the first indicator in detecting the deficit irrigation applied, however, it was not as strongly related to the tree water status as the thermal-based indicators. Thus, the relation between the indicators studied with the stem water potential followed the order: CWSI > Tc-Ta > SWC = Tc. A multiple regression analysis is proposed that combines both soil water content and thermal-based indices to overcome limitations of individual use of each indicator.

Keywords: CWSI; soil moisture; stem water potential; stomatal conductance; thermal-based indices; ‘Bartlett’; ‘Williams’; ‘d’Anjou’.

Grants and funding

This research was funded by the Washington State Tree Fruit Research Commission Technology Committee. LK was partially supported by the USDA National Institute of Food and Agriculture, Hatch project 1014919.