Agricultural mulch can help farmers regulate soil temperature, reduce weeds, and minimize water loss. However, the plastic in commonly-used agricultural mulch can degrade soil and water quality. The microplastics can even enter the food chain. 

In a new study in the Vadose Zone Journal, a publication of the Soil Science Society of America, researchers tested a more sustainable approach to lowering water evaporation from soils. Instead of plastic, they used sand particles coated with soybean oil. In laboratory experiments, soil treated with a thin layer of soybean oil-coated sand had up to 96% lower evaporative water loss compared to bare soil. “These findings show that oil-coated sand has the potential to be developed into a sustainable alternative to plastic film mulch,” says Michael Nicholl, an associate professor at the University of Nevada.

Plastic mulch is made of polyethylene, a hydrocarbon-based product. “It carries long-term environmental consequences,” says Nicholl. “These effects span all stages of its lifecycle: production, installation, and disposal.” Biobased soil coatings – such as soybean oil – could be low-impact alternatives to polyethylene mulch while performing at similar levels.

Initial tests indicated that this oil-coated sand is effective at reducing water loss through evaporation, while allowing liquid water to pass through the layer of oil-coated sand. That suggests this material will not hinder irrigation efforts.

“We hope this work inspires further inquiry into the practical applications of oil-coated materials,” says Nicholl.