Coated sand reduces water wastage

Saudi Arabia’s abundant sand is a symbol of the country’s arid climate. But what if it could help manage a scarce water supply? In the latest instalment of our series on water management, we speak to researchers looking for a way of doing just that.

Agriculture in Saudi Arabia was mostly of a traditional and subsistence nature until the 1970s. As the country’s wealth grew thanks to oil revenue, it developed a modern agricultural sector reliant on freshwater irrigation and became an exporter of produce such as wheat and dates.

But Saudi Arabia has one of the lowest levels of rainfall in the world – less than 100 millimeters (4 inches) per year in most regions. 80% of its food comes from abroad, making it the Middle East’s principal food importer. It has now ended its domestic wheat production program because of the pressure on the water supply. Managing water availability is a priority.

One of the challenges of growing food in a hot, dry climate is that water tends to evaporate. At the King Abdullah University of Science and Technology (KAUST) in the city of Thuwal, researchers are looking at ways of using sand to reduce the amount of water lost in this way.

“Production doubled using the same amount of water”

- Adair Gallo, KAUST

Harnessing nature

Their starting point is that some materials are hydrophobic – in other words, they are repulsed by water. Think of water added to oil in a frying pan and you’ll get the general idea. KAUST Assistant Professor of Environmental Science and Engineering Himanshu Mishra explains the natural principle at play: “Look at any leaf, any flower, any little insect; they have all evolved strategies to not get wet. And typically, it’s very simple; they have a rough, waxy coating. That combination makes them ‘superhydrophobic’: if a drop of water lands on them, it just bounces off.”

Growing produce in the desert (all images courtesy KAUST).

A low-cost approach

Mishra’s team has developed a type of superhydrophobic sand that repulses water. Used on the surface of the soil, it prevents water in the ground from evaporating, thus enabling better nutrient intake and heat management for plants in arid regions. The special sand is simply applied as a layer of mulch, about 5 millimeters (0.2 inches) thick.

The principle couldn’t be much simpler. In fact, this approach has been attempted before, but Mishra points out that crucially, the KAUST lab has found a way to produce the sand at a low cost which means it could potentially be made widely available.

“We started with sand and some high-purity chemicals and it worked really well,” says Mishra. “Then we thought we could make the process much cheaper by using paraffin wax. So one day we stopped at the supermarket and bought some candles! The results were good.”

“We’ve made the process much cheaper by using paraffin wax”

- Himanshu Mishra, KAUST

Promising initial results

Mishra has collaborated with agricultural experts at the university to conduct field trials over the past two years. The initial results are promising according to Mishra’s team mate Adair Gallo. “We started with tomato and barley and the results were very impressive,” he says. “ Basically, production doubled for the same amount of water.”

In addition to being relatively cheap to produce, the product can be applied manually, which means it could be a viable option for small-scale farmers in the global South. A patent application has been submitted and further trials are due to start this fall with date palm growers.