UW-Madison scientists testing new soil nutrient sensor this summer

Scientists at UW-Madison this summer are testing a device that senses soil nutrients, which could help farmers make better decisions when fertilizing. 

The sensor technology created by engineers at the university can be used for real-time monitoring of nitrates in soil, which are essential for growing crops. But excess nitrate can move from soil into groundwater, where it can pose a threat to human health and the environment. 

Joseph Andrews, an assistant professor of mechanical engineering who led the research, says these sensors can help farmers “make more precise decisions” on how much fertilizer they need by showing them the nutrient makeup of their own soil. They can help monitor nitrate leaching and guide efforts for reducing that process. 

“If they can buy less fertilizer, the cost savings could be quite significant at large-acreage farms,” Andrews said in a statement. 

Because existing methods for nitrate monitoring are “laborious, expensive” and can’t offer real-time data, Andrew’s team aimed to create a less expensive option drawing on his expertise in printed electronics. 

They used an inkjet printing process to create “potentiometric” sensors, which are thin electrochemical sensors usually used to measure nitrate in liquid. That limitation made it a challenge to adapt them to use in soil, Andrews said. To overcome that hurdle, researchers added a layer of polyvinylidene fluoride, a porous membrane that can allow the passage of nitrate while blocking soil particles. 

It also attracts and absorbs water, the release shows. Andrews says that means any water with nitrate in it gets “preferentially soaked into” the sensor. 

“This is really important because soil also acts like a sponge, and you’re going to have a losing battle for getting moisture to come to your sensor unless you can match the water absorption potential of soil,” Andrews says. 

By mounting the thin sensors onto a kind of sticker that also contains moisture and temperature sensors, the researchers can attach those stickers to a rod that’s then buried in the soil, enabling measurements at multiple depths. 

The sensors have been shown to provide accurate results in two different soil types common to Wisconsin: sandy soil; and silt loam soil. Researchers this summer are deploying 30 sensing rods at UW-Madison’s Hancock Agricultural Research Station and Arlington Agricultural Research Station for further testing. 

“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. 

The research team published a study in March detailing the sensor technology in the journal Advanced Material Technologies. It’s being patented through the Wisconsin Alumni Research Foundation. 

See the release