Trunk Water Potential Measured with Microtensiometers for Managing Water Stress in “Gala” Apple Trees

Abstract

The weather variations around the world are already having a profound impact on agricultural production. This impacts apple production and the quality of the product. Through agricultural precision, growers attempt to optimize both yield and fruit size and quality. Two experiments were conducted using field-grown “Gala” apple trees in Geneva, NY, USA, in 2021 and 2022. Mature apple trees (Malus × domestica Borkh. cv. Ultima “Gala”) grafted onto G.11 rootstock planted in 2015 were used for the experiment. Our goal was to establish a relationship between stem water potential (Ψtrunk), which was continuously measured using microtensiometers, and the growth rate of apple fruits, measured continuously using dendrometers throughout the growing season. The second objective was to develop thresholds for Ψtrunk to determine when to irrigate apple trees. The economic impacts of different irrigation regimes were evaluated. Three different water regimes were compared (full irrigation, rainfed and rain exclusion to induce water stress). Trees subjected the rain-exclusion treatment were not irrigated during the whole season, except in the spring (April and May; 126 mm in 2021 and 100 mm in 2022); that is, these trees did not receive water during June, July, August and half of September. Trees subjected to the rainfed treatment received only rainwater (515 mm in 2021 and 382 mm in 2022). The fully irrigated trees received rain but were also irrigated by drip irrigation (515 mm in 2021 and 565 mm in 2022). Moreover, all trees received the same amount of water out of season in autumn and winter (245 mm in 2021 and 283 mm in 2022). The microtensiometer sensors detected differences in Ψtrunk among our treatments over the entire growing season. In both years, experimental trees with the same trunk cross-section area (TCSA) were selected (23–25 cm−2 TCSA), and crop load was adjusted to 7 fruits·cm−2 TCSA in 2021 and 8.5 fruits·cm−2 TCSA in 2022. However, the irrigated trees showed the highest fruit growth rates and final fruit weight (157 g and 70 mm), followed by the rainfed only treatment (132 g and 66 mm), while the rain-exclusion treatment had the lowest fruit growth rate and final fruit size (107 g and 61 mm). The hourly fruit shrinking and swelling rate (mm·h−1) measured with dendrometers and the hourly Ψtrunk (bar) measured with microtensiometers were correlated. We developed a logistic model to correlate Ψtrunk and fruit growth rate (g·h−1), which suggested a critical value of −9.7 bars for Ψtrunk, above which there were no negative effects on fruit growth rate due to water stress in the relatively humid conditions of New York State. A support vector machine model and a multiple regression model were developed to predict daytime hourly Ψtrunk with radiation and VPD as input variables. Yield and fruit size were converted to crop value, which showed that managing water stress with irrigation during dry periods improved crop value in the humid climate of New York State.

Relating microtensiometer-based trunk water potential with sap flow, canopy temperature, and trunk and fruit diameter variations for irrigated ‘Honeycrisp’ apple

“…The decrease in the daily FRGR and the FDV could be an early water status indicator to detect water deficit conditions for the trees (Figure 2E). Similar sensitivity of apple fruit diameter to water deficit has been reported in several cultivar and rootstock combinations as well as a range of environmental conditions (Morandi et al, 2017;Gonzalez Nieto et al, 2023a). Fruit growth occurred between evening and early morning for days before and after irrigation.…”

“…Two days later on July 13 th , 2022, the pattern was similar with maximum values at dawn and minimum values during the afternoon but with fewer negative values (Figure 3B). This rapid recovery of the trunk and stem water potential has been also observed in 'Golden Delicious'/MM106 and 'Gala'/G.11, with rapid changes of midday and minimum stem and trunk water potentials of more than 0.5 MPa (Doltra et al, 2007;Gonzalez Nieto et al, 2023a).…”

“…Microtensiometers consist of microelectromechanical pressure sensors that are embedded into the trunk (Pagay et al, 2014) and measure trunk water potential. Their measurements have been recently validated in different fruit trees and vines and under different environmental conditions and irrigation regimes with promising results (Blanco and Kalcsits, 2021;Lakso et al, 2022;Pagay, 2022;Conesa et al, 2023;Gonzalez Nieto et al, 2023a). Its continuous data acquisition may provide reliable and robust water status indicators that correspond well to commonly measured plant response traits such as the sap flow rates, the temperature of the canopy or the daily variations of the trunk and fruit diameter.…”

Evaluation of Computer Vision Systems and Applications to Estimate Trunk Cross-Sectional Area, Flower Cluster Number, Thinning Efficacy and Yield of Apple

“…Precision agriculture uses information obtained from temporal data to address variability within an orchard, with the objective of reducing the variability through variable management and increase the crop value [23]. As growers adopt digital technologies, it is critical to validate the precision of the new technologies [1,24].…”

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

“…Although new plant-based approaches that continuously assess tree water status have been recently developed ( Lakso et al., 2022 ; Blanco and Kalcsits, 2023 ; Gonzalez Nieto et al., 2023 ), they are not as widely implemented in commercial fruit tree orchards as soil sensors, which are a major tool for precision irrigation of fruit trees ( Vera et al., 2019 ). Thus, the combination of soil moisture sensors that continuously measure soil water status and plant-based punctual measurements can be an effective solution to assess tree water status and manage irrigation for commercial production.…”