A nature-inspired wax-coated sand could help enhance food production in the desert as freshwater resources dwindle.
Many arid countries are facing serious water security problems. In desert regions such as Saudi Arabia, high temperatures and dry winds accelerate evaporation from the soil and increase transpiration from plants, which consequently need extra water to maintain their ideal temperature and absorb nutrients.
Farmers frequently rely upon unsustainable levels of irrigation to meet their crops’ increased evapotranspiration needs. In some arid countries, plastic sheets are used to curtail evaporation, but the plastic eventually ends up in landfill.
Kennedy Odokonyero, a researcher at King Abdullah University of Science & Technology (KAUST) in Saudi Arabia said, “With over 70% of the country’s freshwater resources used for agriculture, groundwater aquifers that supply 90% of irrigation water are being irreversibly depleted.”
“Our technology will contribute to food production and greening projects in arid regions across the Middle East and beyond.”
In 2016, Himanshu Mishra, associate professor of environmental science & engineering at KAUST, led a team that developed a superhydrophobic material called SandX, comprising grains of sand or sandy soils coated in a nanoscale layer of paraffin wax. The roughness of the sand combined with the naturally impermeable wax to created an extremely water-repellent surface.
“A 5-10mm thick layer of SandX applied like mulch over wet soil greatly reduces evaporation,” said Professor Mishra.
A four-year field study of SandX mulching of tomato, wheat and barley in western Saudi Arabia showed that “SandX significantly improved plant health, size and yield under normal irrigation,” he explained, “but the specific physiological factors underlying these results were unclear.”
Further investigation by Mishra's team looked at the effects of SandX on tomato plants (Solanum lycopersicum) grown in controlled, desert-like conditions alongside a group of unmulched tomatoes for comparison. They tracked water use, plant size and the physiological health of the roots, shoots and fruits of the plants under normal and reduced irrigation.
“SandX could offer a sustainable solution for excessive water consumption.”
Remarkably, the combined balance of evaporation and transpiration remained the same in mulched and unmulched plants. However, SandX mulching reduced evaporation losses by nearly 80%, which enhanced transpiration and benefitted the plants under both irrigation scenarios.
“Mulched plants had a significantly wider root xylem, the vessel that transports moisture and minerals from the root through the stem, which improved water and nutrient uptake from the soil,” says Odokonyero. And just as the team observed in their field tests, the fruit yields of the mulched tomatoes were around 30% higher than the unmulched counterparts.
“SandX could offer a sustainable solution for excessive water consumption,” says Odokonyero.
Field trials are already underway on different crops and native trees in Saudi Arabia, and the team has begun scaling up SandX production after receiving KAUST’s Innovation and Economic Development grant.
“Our technology will contribute to food production and greening projects in arid regions across the Middle East and beyond,” concludes Mishra.