Experts at the University of Wisconsin-Madison are printing soil sensors that could help to save farmers money and limit problematic nitrate pollution.
They created palm-sized sensors through an inkjet printing process. The thin, film-like, electrochemical devices are great at measuring nitrate levels in liquids. Part of the breakthrough in Wisconsin came by adapting the tech for use in soil, thereby keeping an eye on nitrate levels, according to a lab report.
Nitrogen is a key part of common fertilizers. When excess nitrogen is washed off fields, it can pollute and harm organisms in lakes, rivers, streams, and drinking water. The latter can be a hazard to people. The United States Geological Survey reports that 41% of nitrogen "delivered" to the Gulf of Mexico is a result of agricultural fertilizer.
"Our sensors could give farmers a greater understanding of the nutrient profile of their soil and how much nitrate is available for the plants, helping them to make more precise decisions on how much fertilizer they really need," university Assistant Professor Joseph Andrews, who led the research, said in the summary.
Better fertilizer management can also be an economic boon for farmers. Fertilizer costs vary from year to year. In 2023, the most recent data published by the USDA, fertilizer cost $186.73 an acre, down from a high since 2022 of $225.78.
"If they can buy less fertilizer, the cost savings could be quite significant at large-acreage farms," Andrews added.
To adapt the sensors for use in soil, the engineers placed a polyvinylidene fluoride layer over them. The film has ultra-small holes — on the nano level — that let nitrates enter, but not dirt. The material also attracts and absorbs water like a sponge, per the lab report.
The layered sensors are able to allow just enough nitrate-laden water to pass to get an accurate reading. The experts intend to measure multiple soil metrics by placing the sensors in rods and putting them into fields at varied deepness.
"The main challenge we were trying to solve is figuring out a way to enable these electrochemical sensors to work well in the harsh environment of soil and accurately sense nitrate ions," Andrews said in the summary.
There are about 876 million acres of farmland in the U.S., a decrease from 945 million acres in 2000, data collector Statista notes. Fertilizer helps to grow reliable yields to feed the continually growing global population. Finding safer, effective ways to manage fertilizer use is the topic of research in other labs, as well. Researchers at the University of Texas-Austin are developing a hydrogel that can capture excess nitrogen before it leaves the field.
The research is part of the way we can work to make our food system more planet-friendly. You may not have acres of land on which to farm, but even a backyard garden can produce a fridge full of fresh, DIY food. A $70 investment could lead to $600 of fruit and vegetables with the right approach.
As for the big picture, the Wisconsin team planned to test their devices with 30 rods on a university field this summer.
"By measuring the nitrate, moisture, and temperature at different depths, we can now quantify the process of nitrate leaching and capture how nitrate is moving through the soil, which hasn't been possible before," Andrews said.
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