Biodegradable Sensors Deliver Important Soil Health Data — and Turn Into Plant Food Afterwards

Researchers from the University of Glasgow, the Central South University of Forestry and Technology, and the Institute of Microelectronics and Photonics have come up with a way to improve sustainability in data-led modern agriculture: compostable smart sensors.

"Reliable food production is one of the world’s most pressing problems, with more than 800 million people around the world suffering from malnutrition today," explains co-author Joseph Cameron of the issue the team is hoping to address. "Digital agriculture could be the key to maximizing our ability to produce enough food for a growing population."

Data-driven "digital agriculture," though, can spell trouble for the environment: deploying vast quantities of devices for monitoring soil health can, ironically, damage that same soil, and contribute to the growing e-waste problem around the world. But what if those sensors could both monitor the soil and help its health, while still providing valuable data for growers?

"The system we've developed could go a long way towards cutting down the carbon footprint of digital agriculture. The sensors themselves can be plowed back into the fields to help nurture crops, and the electronic modules with less environmentally friendly printed circuit materials can be reused for several years," explains co-author Andrew Rollo. "Our analysis suggested that replacing the sensors once every three months could reduce the environmental impact of the system by 66%, and 79% over five years compared to disposing of the entire device each time."

The sensor developed by the team combines a biodegradable patch with a reusable electronic module roughly the size of a matchbook and powered by a Microchip ATmega328P microcontroller communicating over a Zigbee wireless network. Manufactured using a screen printing process, the patch is the only part of the system that needs to be replaced regularly — and when it does, its polymer substrate, graphene-carbon ink, and molybdenum disulfide sensing layer all naturally degrade into nutrients for next growing season's plants.

In lab testing, the sensors proved able to monitor the pH level of soil in samples ranging from pH 3 to pH 8 over a two-week period — and also capable of detecting ethephon, a plant growth regulator that is toxic to humans and wildlife and must be accurately tracked in its use in order to prevent groundwater contamination.

"We urgently need to find a way to make digital agriculture more sustainable in the years to come. Currently, around 80% of the world’s electronics head straight to landfill once they’ve reached the end of their useful life, which creates massive environmental and public health challenges from the toxic materials which many of them contain," says project lead Jeff Kettle.

"We're keen to continue expanding our biodegradable sensor's ability to detect other key indicators of plant growth and soil health. That could include adding sensitivity to 'forever chemicals' like PFAs, which have significant environmental impact."

The team's work has been published in the journal ACS Applied Electronic Materials under open-access terms.