Wax-coated sand could help arid farm regions

Wax-coated sand could help arid farm regions
Mar 23, 2022

Wax-coated sand keeps soil wet longer, improves crop yields in arid regions according to new study.

By Andrew Joseph, Farms.com; Image: Adapted from ACS Agricultural Science &Technology 2022, DOI: 10.1021/acsagscitech.1c00148

A new study recently published in ACS Agricultural Science & Technology shows that wax-coated sand--a simple, biodegradable ground cove—will keep soil wet ad increase crop yields in arid farming climes.

In North America, which has seen drought like conditions greatly affect its crop yield in 2021, results from a research team led by Associate Professor Himanshu Mishra and researchers from the Saudi Arabia's King Abdullah University of Science and Technology could be good news.

Yes, dry and hot regions are difficult places to grow crops because the soil dries out quickly, which means farmers will counter by irrigating their fields with buried networks of irrigation tubing and/or cover the ground with plastic sheets. Even then, it does not guarantee a crop can get the water it needs before the heat dries up the water supply.

According to the American Chemical Society, Professor Mishra and colleagues wanted to see if they could coat sand with wax to create an environmentally benign ground cover to control soil evaporation.

The result: purified paraffin wax-coated Superhydrophobic Sand (SHS).

Purified paraffin wax was chosen as it is a biodegradable substance and readily available in large quantities.

The team initially dissolved the wax in hexane and poured silica sand into the mixture. As the solvent evaporated, a 20-nm-thick coating of wax was left behind on the sand grain—however, this process has now been refined where no solvents are required.

The team applied this wax-coated sand in a thin layer atop an open field in Saudi Arabia, and measured a decrease in the loss of soil moisture of 50- to 80-percent.

When the SHS was used over multiple growing seasons as a 5- to 10-mm-thick mulch for wheat, barley and tomato plants, those plants produced up to 73 percent more grain and fruit than a group of control plants grown in uncovered soil.

Importantly, the microbial community around the plants’ roots and in the soil was not negatively impacted by the waxy mulch, which could have acted as a food source for some of the microbes. This simple nature-inspired technology could make water use more efficient in arid regions, the researchers hope.

For those wondering if wax paraffin is actually a “green” product, it’s not—at least not in its regular form. Professor Mishra, however, said his research team used a purified "food-grade" wax which is non-toxic and biodegradable, meaning no environmental damage or accumulation in the ground.

"Depending on the wax coating thickness and environmental conditions, SHS degrades over time under microbial action at the soil-SHS interface," said Professor Mishra. "In our experiments … SHS lost its water repellency within about nine months—this means that SHS grains lost their waxy coating. On tilling, they simply got incorporated into the sandy soil like a drop in the ocean.

Therefore, under our environmental conditions, successive crop cycles with SHS do not cause wax accumulation."

Professor Mishra acknowledged that a study out of the University of Nevada, Las Vegas (UNLV) in 2020 had used a soybean oil to coat the ground, but countered that his team’s SHS was more hydrophobic.

This implies that less SHS mulch would be needed to achieve the moisture retention, and since the SHS technique is less complex to replicate, it could more easily be scaled up for wider usage.

Download the report from ACS Publications: https://pubs.acs.org/doi/full/10.1021/acsagscitech.1c00148.

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