Improving irrigation efficiency of date palms
Integrating electrical resistivity tomography and sap flow measurements within agro-ecosystem models to improve irrigation efficiency of date palm (PALM-IRRI) / Integration von elektrischen Widerstandstomographie und Saftflussmessungen in Agrarökosystemmodelle zur Verbesserung der Bewässerungs- effizienz von Dattelpalmen (PALM-IRRI)
01.06.2019 – 31.05.2022
Forschungszentrum Jülich GmbH,
Ben Gurion University of the Negev
The cultivation of date palms in the hyper-arid Arava and Jordan valleys is widespread and exclusively depends on high-frequency irrigation. Large amounts of water are usually applied for meeting the evapotranspiration demand of date palm, despite local agricultural water quota constraints. In order to better understand water use of date palms (and many other trees), much attention has been paid to using sap flow measurements with heat dissipation sensors to determine transpiration rates. However, the calculation of whole-tree water use from point-scale sap flow measurements is challenging in general due to the empirical sapwood area estimation and the heterogeneous xylem hydraulic conductivity. In addition, date palms are known to have a large internal stem water reservoir that is used for transpiration in daytime when the evaporative demand exceeds the water supplied by roots and recharged at night. This diurnal water allocation in the stem is crucial to the photosynthetic performance of date palms, as it enables optimal vegetative and reproductive growth in hot and dry deserts, but its dynamics are still poorly understood because of a lack of methods to quantify stem water content.
The main hypothesis of the PALM-IRRI project is that electrical resistivity tomography (ERT), a widespread geophysical technique for imaging sub-surface structures, enables improved transpiration estimates from sap flow measurements and the assessment of stem water dynamics. The overall objective of this project is to combine sap flow and ERT measurements to obtain improved estimates of transpiration and stem water content of date palm, and to use this novel sensor combination to calibrate a soil-plant-atmosphere model that will subsequently be used for irrigation scheduling.
Within the project, laboratory experiments on date palm stem segments will first be used to establish relationships between electrical properties and water content of the stem, as well as to establish a procedure to upscale point-scale sap flow measurements to the entire tree using ERT. Field experiments will be conducted in the Central Arava and Jordan rift valleys. First, single date palm tree investigations will be used to investigate stem water content dynamics using ERT and sap flow measurements. Second, measurements will be carried out in date palms trees grown in weighing lysimeters with different irrigation levels to evaluate the accuracy of transpiration estimates obtained by combining ERT and sap flow measurements. Based on these laboratory and field experiments, a soil-plant-atmosphere continuum model will be calibrated for date palms, and used to optimize date palm irrigation scheduling. In a final step, the performance of the optimized irrigation scheduling will be compared to conventional irrigation in terms of water use and agricultural productivity.
The project is funded by the German-Israeli Water Technology Cooperation programme within the FONA framework programme for research on sustainable development of the BMBF. The project is administered by Projektträger Karlsruhe (PTKA), Bereich Wassertechnologie.