Nadler, A., Institute of Soil, Water, and Environmental Sciences, ARO, Bet Dagan, 50250, Israel
Raveh, E.
Yermiyahu, U.
Green, S., Environmental Group, HortResearch, Private bag 11-030, Palmerston North, New Zealand

Close, direct, and accurate monitoring of the plant water status may serve as a practical (irrigation scheduling) and a research (climate-environmental induced physiologic changes) tool. Methods for high-frequency capacitance measurement (e.g., time domain reflectometry [TDR]) possess the potential for high resolution dielectric measurements with minimal dependence on properties of the measured matrix. The objective of this study is to test the accuracy, response time, and sensitivity of the TDR methodology in measuring changes in water status in a mango (Mangifera indica L., Cultivar 'Kent') tree stem exposed to several perturbations concerning water, salinity, fruit load, and radiation. Under several induced stress conditions, stem and root zone water content (θ) and electrical conductivity (σ) were simultaneously measured. Our study is distinct in its detailed and frequent measurements of stem water content (θstem) using short (29-70 mm) TDR probes in trees growing in a detached medium. We have found that θstem response to root zone applied salinity and water stress were negative and positive, respectively. Stem electrical conductivity (σstem) was primarily dependent on θstem and only negligibly on stem cells salinity. The θstem response time to water application was ∼4 h. Two practical outcomes of our study were: (1) Because the salt content of the tree cells only slightly affected σstem, stem resistivity measurements could be used to represent dielectric changes, and (2) quite short probes could be used to include young trees of slim tree branches. © Soil Science Society of America.