Self-watering Soil Could Transform World Agriculture

Scientists have come up with a new type of soil that provides its own water, extracting moisture straight from the air.

A new type of soil created by engineers at the University of Texas (UT) draws water from the air and distributes it to plants, essentially removing the need for rain in the germination and growing process of plants.

The discovery promises to revolutionise farming techniques across the globe, potentially expanding the map of farmable land to previously barren, in arable places and reducing water use in agriculture at a time of escalating droughts.

The scientific team from UT in Austin, Texas, published its findings in the journal ACS Materials Letters, which describes the development of an atmospheric water irrigation system that 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.

“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,” said Guihua Yu, associate professor of materials science in the Walker Department of Mechanical Engineering at UT.

Growing food without rain

Each gram of soil can extract approximately 3-4 grams of water. Depending on the crops, approximately 0.1 to 1 kilogram of the soil can provide enough water to irrigate about a square meter of farmland.

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 soil.

The team ran experiments on the roof of UT engineering building to test the soil. They found that the hydrogel 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 per cent 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.

“Most soil is good enough to support the growth of plants,” said Fei Zhao, a postdoctoral researcher and team leader. “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 water-harvesting soil is the first big application of technology that Yu’s group has been working on for more than two years. Last year, the team developed the capability to use gel-polymer hybrid materials that work like “super sponges,” extracting large amounts of water from the ambient air, cleaning it, and quickly releasing it using solar energy.

The researchers envision several other applications of the technology. It could potentially be used for cooling solar panels and data centres. It could expand access to drinking water, either through individual systems for households or larger systems for big groups such as workers or soldiers.