ABU DHABI // Half a metre under the surface of Yas Island, an experiment is under way that could dramatically cut the UAE's water use.
Irrigation accounts for about 80 per cent of the water used by the UAE, with traditional irrigation - such as drip or spray systems - using 12 to 15 litres of water a day per square metre of land. In contrast, an environmental company says its new system uses less than three litres.
Epic Green Solutions hopes to demonstrate the efficiency of the "closed" or subsurface irrigation technology at trial plots on Yas Island and in Al Ain.
To prepare the land, the area is excavated 60cm deep and a rubber liner placed at the bottom and on the sides. Pipes are then placed on top of the liners. Water flows into the system, through the pipes and out of holes along their base before reaching the plants' roots.
Above the system is a 10cm-thick layer of gravel which allows the water to travel easily across.
"Everything above the gravel is sand so when the water makes contact with [the sand], we get a capillary draw that sucks the water up," said Bart Rehbein, Epic's managing director. "Just like a sponge on a puddle."
Not only does the technology act as a system for storing and managing water, it "harvests" rain and controls pollution with biofiltration. And because all the water is underground, there is little evaporation, Epic says. Sensors constantly monitor the moisture in the soil, aiming to keep it between 70 and 80 per cent saturated. When it falls below that - every four to six hours - the pumps are switched on to add more water.
The system uses treated sewage effluent, municipality water or recycled wastewater, known as greywater. "We can also use saline water for plants that are able to survive on it such as sesuvium," Mr Rehbein said.
Delivering the water underground solves another problem with traditional saline irrigation - the layer of encrusted salt left on plants' leaves as the water evaporates.
"The plant can't absorb any of the water and it has the same effect as a herbicide - it basically kills it," said Mr Rehbein. "We live in a dry environment so it's important to have a closed irrigation system."
The Abu Dhabi Government aims to cut water use in the emirate's 25,000 farms.
"For the past 30 years, the UAE's groundwater has been dropping one metre per year and the wells are drying up," Mr Rehbein said.
Some 880 million cubic metres of water are taken out of the ground every year, and only 220 million are put back in.
"I've seen a marked difference in the attitude of government officials about water consumption, especially in the last year or two."
Nicholas Lodge, the managing partner of the agricultural consultancy Clarity in Abu Dhabi, said subsurface irrigation was "beneficial from an agricultural point of view because you have less evaporation and therefore less waste".
"But conventional farming in this environment doesn't make a huge amount of sense," he said. "The problem with subsurface irrigation in the region is farming in a sandy ground."
He added that such a lot of water would need to be run through the soil that "there's very little ability for the soil to retain any nutrients".
Water would leave the soil's root zone quickly, so the plants received the nutrients but there would be a need to keep adding water, "which means high water consumption", he said.
Another problem was that the treated sewage water meant there was a high risk of contaminating the soil and the crop. "It's not without its drawbacks or potential risks so we have to be careful," he said.
"Low water input systems, where water is recycled and overall water usage is reduced, are the areas where people should look for the future."
If the trial is successful, Epic is hoping its system will be installed in farms across the UAE. "But we're not quite there yet," said the managing director.
In Al Ain, two crops of cucumbers were grown in a greenhouse, half irrigated by a traditional drip system and half by Epic's system. "We used 80 per cent less water on our side, half as much fertiliser and we're producing 50 per cent more cucumbers," Mr Rehbein said.
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