This self-watering soil could revolutionise farming

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A new type of soil, created by engineers at the University of Texas at Austin, can extract water from the air and retreat into the soil, potentially expanding the map of agricultural land around the world to previously inhospitable places and reducing agricultural water consumption in times of growing drought. The atmospheric irrigation system, published in ACS Materials Letters, uses a super-moisture-absorbing gel to trap water in the air.

We have alrady covered vertical farming as a revolutionary and more sustainable method of agriculture in the past and self-watering soil could be another sustainable solution to human needs.

When the soil is heated to a certain temperature, the gel releases the water and makes it accessible to the plants. When it distributes water, it goes back into the air to increase moisture and facilitate the continuation of the harvesting cycle.

Each gram of soil can produce about 3 to 4 grams of water, and depending on the area it is grown, this can provide enough water to irrigate up to 1,000 hectares of crops or about 1.5 million hectares.

The water is generated by the solar heat of the day and contains a gel that releases its contents to the ground. At night, during the cooler, moist phase, the yellow soil draws water from the air and converts it into the water, which is then excreted.

The team conducted experiments to test the ability of self-watering soil to irrigate itself on the ground. In a miniature greenhouse, the researchers planted radishes in self-watered soils and compared them with sandy soils in drier regions of the world.

They found that the hydrogel soil not only stored water but also required much less water to grow the plants. After four weeks of experiments, the team found that their soil had retained enough water to start releasing as much water as before. Sandy soils, on the other hand, had only one week of it and only a few days of water retention.

In another experiment, the team planted radishes in both soil types, but the radish in the hydrogel soil survived the first round of irrigation needed to root the plant. In the second round, however, they had to be watered twice as often as on sandy soils.

“Most soils are good enough to support plant growth”, said Xingyi Zhou, a postdoctoral researcher in Yu’s research group, who led the study with Xedyi, Zhou and Panpan Zhang.

“We wanted to develop a soil that could draw water from the ambient air, but water is a big limitation.” 

Yu’s group has been working on it for more than two years, and water extraction and soil extraction are the first major applications of the technology. Last year, the team developed a super sponge made of a gel-polymer hybrid material that works as a kind of super sponge, a kind of water harvester. The super sponges extract large amounts of water from the ambient water, purify it, release it quickly with solar energy and store it in the soil.

The researchers see several other applications for the technology: it could potentially be used to cool solar cells in data centres, expand access to drinking water, and even power plants.

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