Water use and irrigation requirements for date palms on commercial farms in the hyper-arid United Arab Emirates

The production of dates in the hyper-arid deserts of the United Arab Emirates (UAE) is economically and culturally important. All of the commercial date palms need to be irrigated, and the prime source of this water is groundwater. However the quantity and quality of the groundwater resources in the UAE are being compromised by groundwater extraction at 25 times the rate of recharge, and a rise in salinity as the reserves dwindle. Rates of groundwater use on commercial farms need to be the minimum required for date production and the leaching of salts from the rootzone. We have shown that tree water use, ETc, can be predicted from 0.95 LI x ETo where LI is the fraction of incoming visible light intercepted by the canopy, and ETo is the reference evapotranspiration. We now surveyed 10 commercial date farms in Abu Dhabi and determined the LI of date canopies by proximal sensing with a light-stick across a range of tree densities, tree ages, and groundwater salinities. We were able to link LI to the fractional ground cover, FGC, obtained by analysis of satellite images. Thus it was possible to determine ETc of date palms across all of these commercial farms, and potentially all the UAE. The median ETc of the 10 farms was 70 kL y(-1), which was about twice that observed in our experiments at a research station near Dubai. Some 10% of the trees on these commercial farms were predicted to use over 100 kL y(-1). It is suggested that irrigation should be at 1.5 x ETc to account for a 25% factor-of-safety, and a 25% salt-leaching fraction. Reductions in irrigation would be achieved by more aggressive pruning of the fronds to reduce LI, and hence ETc, without compromising date yield.