It is critical to regulate soil temperature, reduce water loss and decrease weeds for the proper growth of crops. Farmers can fulfil all these requirements of growing good crops with the help of agricultural mulch.
However, plastic may also be present in the mulch. It can reduce water quality and degrade the soil. Moreover, microplastics can also enter the food chain and have harmful impacts.
Recent research, published in the Vadose Zone Journal, evaluates different approaches for lowering evaporation from soils. They used sand particles coated with soybean oil instead of plastic. The research was led by Micheal Nicholl, an associate professor at the University of Nevada.
Researchers observed 96% less evaporative water loss in soil coated with a thin layer of soybean oil. Thus, oil-coated sand is a potential candidate to replace the plastic film mulch.
Why do we need to avoid plastics?
Plastic is a derivative of a hydrocarbon-based product called polyethene. According to Nicholl, it causes long-term health issues. The impacts of plastics may occur in any stage of their life cycle: production, installation and disposal.
Alternative to plastics:
A low-impact alternative to polyethene plastic is Biobased soil coatings. These Biobased soil coatings, such as soybean oil, have similar performance to plastics.
- In the first step, researchers mixed equal quantities of oil and sand to make coated sand.
- In the second step, they heated the sand mixture for an hour.
- In the next step, the mixture is allowed to cool.
- Finally, they wash and dry the mix to get the coated sand.
This process polymerizes the oil and induces modifications in it. The modified oil forms a layer around the individual sand particles.
Initial examination indicated the effectiveness of the oil-coated sand in minimizing water loss.
There are two ways of water evaporation. But the oil-coated soil act on the most robust path to stop evaporative water loss.
To explain the first process, Nicholl considered soil a damp sponge. The sponge soaks all the water when placed in water. Eventually, the water will rise to the sponge top and evaporate.
Wicking action also works in the same way and causes direct evaporation of water. In this process, water can’t reach the soil surface and get evaporates into the soil air. This humid air then moves through the soil and escape.
According to Nicholl, wicking action is less efficient and causes low evaporative water loss.
The Nicholl research aims at finding out if it is possible to both ways of evaporative loss with a surface layer of oil-coated sand.
To conduct the research, the research team filled the test soils in the PVC columns. In the next step, they covered the column with oil-coated sand. In the last step, they made the columns water saturated.
Once the experimental set-up was arranged, the team evaluated the evaporative water loss for each column.
The study concluded that the soil-coated sand decreases the amount of wicking water. So, there will be less water loss through evaporation.
However, researchers weren’t sure whether they could coat a single soil particle or not. Moreover, there are also chances for oil and sand to get cemented.
“We found instead that individual sand grains can be coated with partially-polymerized oil,” says Nicholl.
That’s important because any soil treatment to reduce water loss also has to allow water – via rainfall or irrigation – to enter the soil. A sheet of oil-coated sand fused together could stop water from entering the soil.
This is significant because any soil treatment intended to reduce water loss may disturb the water for irrigation to enter the soil. So, the oil-coated sand film may disrupt the water irrigation system.
But the laboratory tests concluded that oil-coated sand allows water for irrigation to enter the soil. It doesn’t hinder the irrigation efforts.
“Though initial results are encouraging, there are many questions still to answer,” says Nicholl.
According to Nicholl, they can’t determine the response of material weather in an agricultural setting. It’s because of the non-exposure of biobased mulch to the outdoor environments.
Now researchers are looking forward to exploring the procedures to measure the durability of coated material in different environments. These environmental settings may include biologically active soils, temperate climates, and arid environments.
“We hope this work inspires further inquiry into the practical applications of oil-coated materials,” says Nicholl.