To prevent water from evaporating in the soil, farmers usually cover the ground around the crop plant with a layer of polyethylene plastic. But soon there will be a more environmentally friendly alternative, the form of soybean oil clad in sand. When most people hear the word “covering”, they think of organic materials such as bark or dead leaves. However, the often-used agricultural plastic sheeting is also a form of mulch that, in addition to helping to keep the soil moist, can also reduce weed growth, prevent soil erosion, and increase soil temperature by creating a ground-based greenhouse effect.
However, like other plastic products, the production process of sheet metal is not a very environmentally friendly process. In addition, once the plastic covering is cracked and broken, it is usually only removed and dumped in the dump. What’s more, its tiny particles may remain in the soil and may even enter the harvested crop.
Led by Associate Professor Michael Nicholl, scientists at the University of Nevada, Las Vegas, have begun developing a more environmentally friendly alternative that provides similar water preservation.
They first combined the same amount of sand with soybean oil, heated the mixture for about an hour, and then let it cool down. This process aggregates the oil parts, forming a coating around each grain of sand. Finally, wash the coated sand in water and let it dry to remove excess oil.
In laboratory tests, a layer of oil sands is placed on the various types of soil contained in the vertical part of the PVC tube and then soaked with water. It has been observed that water flows easily through the sand into the soil. The challenge, however, is how to keep the liquid there.
“When water is applied to the surface of the soil (rainwater, irrigation), some water penetrates downwards under capillary and gravity,” Nicholl explains. “After the water is cast, the soil starts to dry from the top down. As the top surface becomes drier, capillary action causes water in deeper and weer soil to rise upward, where it evaporates on the surface and enters the atmosphere directly. “
Due to its hydrophobic (water-resistant) properties, the oil coating helps prevent this from happening – even though the water is still flowing upstream through the soil, it is essentially “in turn” by the sand, making it impossible to evaporate. Overall, the study found that the evaporative moisture loss of sand-covered soil was as high as 96% compared to the control samples of bare soil.
“These results suggest that oil-packed sands have the potential to be developed as sustainable alternatives to plastic film mulch,” Nicholl said.
The paper on the study was recently published in vadose Zone Journal.