Engineers at the University of Texas at Austin, USA, have created a self-watering soil that can pull water from the air and distribute it to plants, potentially expanding the map of farmable land around the globe.
As published in ACS Materials Letters, the team’s self-watering soil uses super-moisture-absorbent gels to capture water from the air. When the soil is heated to a certain temperature, the gels release the water, making it available to plants. When the soil distributes water, some of it goes back into the air, increasing humidity and making it easier to continue the harvesting cycle.
Guihua Yu, associate professor of materials science in the Walker Department of Mechanical Engineering, said: “Enabling free-standing agriculture in areas where it’s hard to build up irrigation and power systems is crucial to liberating crop farming from the complex water supply chain as resources become increasingly scarce.”
The gels in the soil pull water out of the air during cooler, more humid periods at night. Solar heat during the day activates the water-containing gels to release their contents into the soil. Each gram of soil can extract approximately 3-4 millilitre of water. Depending on the crops, approximately 0.1 to 1 kilogram of the soil can provide enough water to irrigate about a square metre of farmland.
Fei Zhao, a postdoctoral researcher in Yu’s research group, said: “Most soil is good enough to support the growth of plants. It’s the water that is the main limitation, so that is why we wanted to develop a soil that can harvest water from the ambient air.”
The team tested the soil on the roof of the Cockrell School’s Engineering Teaching Center at the University of Texas at Austin. They found that the self-watering soil was able to retain water better than sandy soils found in dry areas, and it needed far less water to grow plants.
During a four-week experiment, the team found that its soil retained approximately 40% of the water quantity it started with. In contrast, the sandy soil had only 20% of its water left after just one week.
In another experiment, the team planted radishes in both types of soil. The radishes in the hydrogel soil all survived a 14-day period without any irrigation beyond an initial round to make sure the plants took hold. Radishes in the sandy soil were irrigated several times during the first four days of the experiment. None of the radishes in the sandy soil survived more than two days after the initial irrigation period.
The researchers have outlined several other applications of the technology. It could potentially be used for cooling solar panels and data centres. It could also expand access to drinking water, either through individual systems for households or larger systems for big groups such as workers or soldiers.
