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The impact of replacing groundwater by treated sewage effluent on the irrigation requirements of Al Ghaf (Prosopis cineraria) and Al Sidr (Ziziphus spina-christi) forests in the hyper-arid deserts of Abu Dhabi

The arid forests of Abu Dhabi are valuable but they require irrigating.‎ Currently groundwater (GW) is the source of this water, but these subterranean reserves are being over-exploited.‎ Law No 5 of 2016 on the regulation of GW has been passed by the Government of Abu Dhabi to reduce GW abstraction.‎ Abu Dhabi has a supply of tertiary-treated sewage effluent (TSE) that could be used as an alternative for irrigation.‎ We set up experiments near Madinat Zayed in the Al Dhafra region of Abu Dhabi on two arid-forest species: Al Ghaf (Prosopis cineraria) and Al Sidr (Ziziphus spina-christi).‎ The trees were planted at 8mx 8m spacing.‎ The TSE is significantly ‘sweeter’ than GW, as its electrical conductivity is<1 dSm−۱, whereas GW is 8–10 dSm−۱. The GW in this region is very high in nitrates (38.‎4 ± 9.‎2 mg-NO3 L−۱), and this was not significantly different from the TSE (53.‎7 ± 11.‎8 mg-NO3 L−۱). We monitored the actual tree water-use (ETc, L h−۱) via heat-pulse devices in both the GW and TSE-irrigated trees.‎ We quantified the differences in the ETc patterns for both the GW and TSEirrigated trees of both species over 3 years.‎ Both species showed positive growth-responses to TSE, relative to the GW, and we consider this to be due to the lower electrical conductivity of the TSE water.‎ Because of this growth response the ETc of the TSE by the Ghaf trees was, on annual average 17% higher than GW, and for the Sidr it was 39%.‎ Our results were corroborated by leaf conductance and leaf-area inferences.‎ But for TSE there is no need for a salt-leaching fraction.‎ Furthermore, to achieve the same tree-health outcome as with the GW, even less TSE need be applied.‎ Irrigation requirements for TSE were at least 25% less than for GW.‎

Authors: 
Wafa Al-Yamani, Steve Green, Rommel Pangilinan, Steve Dixon, Shabbir A.‎ Shahid, Peter Kemp, Brent Clothier
Year: 
۲۰۱۹
Publication type: 
Scientific Paper
Publication Source: 
Agricultural Water Management
Volume/Chapter/Issue: 
۲۱٤
Page Number: 
۲۸ - ۳۷