Drought responses in three apple cultivars using an autonomous sensor-based irrigation system

Authors: Bierer, Andrew; Tang, Lisa

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2024
Publication Date: 2/26/2024
Citation: Bierer, A.M., Tang, L. 2024. Drought responses in three apple cultivars using an autonomous sensor-based irrigation system. HortScience. 59(4):431-441. https://doi.org/10.21273/HORTSCI17520-23.
DOI: https://doi.org/10.21273/HORTSCI17520-23

Interpretive Summary: The management of water resources in the commercial production of temperate tree fruit is shifting towards data-driven decision support platforms, commonly relying on measurements of soil moisture. In contrast, classical standard interpretations of water stress in plants are physiological in nature and currently reliant on costly specialized equipment and labor-restrictive techniques prohibitive for commercial adoption. Therefore, this study sought to divulge relationships between standard physiological measures of plant water stress and the more accessible measurement of soil moisture status in pursuit of improving irrigation decision support systems. An autonomous sensor-based irrigation system, Open_Irr, was utilized to impose four levels of soil moisture status on three apple varieties: ‘Autumn Gala’, ‘Crimson Crisp’, and ‘Golden Delicious’, while aspects of plant physiological function were assessed. While general correlation between soil moisture status and physiological measurements were low, several useful data shapes were identified through nonlinear regression which, when refined, could be incorporated into decision support systems. Additional efforts to describe the relationship between physiological function with more scalable monitoring systems is advised.

Technical Abstract: Irrigation decision support systems evolving in the domestic temperate tree fruit production industry are reliant on measures of soil moisture status, diverging from classical physiological indicators of edaphic stress. This study utilized an autonomous sensor-based irrigation system to impose water deficit (soil matric potential targets of -20, -40, -60, -80 kPa) on ‘Autumn Gala’, ‘Crimson Crisp’, and ‘Golden Delicious’ apple (Malus domestica) varieties grafted to Budagovsky 9 rootstock in the greenhouse (n=60). It was hypothesized that relationships between physiological plant function, assessed via infra-red gas exchange and chlorophyll fluorescence, and soil moisture status may be utilized to advance emerging irrigation decision support systems. Complications arising from defoliation by day 11 at -60 and -80 kPa advise generation of substrate-specific soil water relationships in research applications of autonomous sensor-based irrigation systems. ‘Autumn Gala’ C assimilation rates at -80 kPa declined from day 0 to day 8 (9.93 and 5.86 umol CO2 m-2 s-1), while transpiration rate was maintained, potentially reducing observed defoliation as other varieties increased transpiration to maintain C assimilation. Correlation matrices revealed Pearson’s “r” = |0.43| for all physiological metrics considered with soil matric potential, nevertheless, exploratory regression analysis on leaf water potential at dawn, C assimilation (A), transpiration (E), stomatal conductance (gs) and non-photochemical quenching (NPQt) exposed speculatively useful data-shapes warrant of study. Nonlinear piecewise regression suggested soil matric potential may be used as a predictor of at dawn leaf water potential; the critical point bridging the linear spans, -30.6 kPa, could utilized in irrigation decision support systems.