Sustainable smart agriculture with a biodegradable soil moisture sensor

Researchers from Osaka University developed wirelessly powered soil moisture sensing technology that will help meet the needs of sustainable precision agriculture. Both the soil moisture content and the position of each sensor are readily detected and transmitted, even at high sensor densities. The sensors are largely biodegradable and can be tilled into the soil at the end of the crop season. This work might help farmers allocate resources to cropland in a timely, targeted manner.

Fig. 1
Proposed sensing system. a) Overview of the proposed sensing system with degradable sensor devices. b) When power is wirelessly supplied to the degradable sensor devices placed on the soil, the device heaters activate. The sensing location is determined from the hotspot location, and the temperature of the heater varies with the soil moisture content; thus, the soil moisture content is measured from the hotspot temperature. c) The degradable sensor devices are tilled into the soil after use. Subsequently, fertilizer components in the substrate of the sensor device are released into the soil, stimulating crop growth

Researchers from Osaka University use biodegradable sensors to measure and wirelessly transmit soil moisture data, which with further development might help feed an increasing global population while minimizing resource use for cropland

Osaka, Japan – Increasingly limited land and water resources has inspired the development of precision agriculture: use of remote sensing technology to monitor air and soil environmental data in real time, to help optimize crop output. Maximizing the sustainability of such technology is critical to proper environmental stewardship and reducing costs.

Now, in a study recently published in Advanced Sustainable Systems, researchers from Osaka University have developed a wirelessly powered soil moisture sensing technology that is largely biodegradable and therefore can be installed in high densities. This work is an important milestone in removing the remaining technical bottlenecks in precision agriculture, such as safe disposal of used sensor devices.

With an increasing global population, it is imperative to optimize agricultural output yet minimize land and water use. Precision agriculture aims to meet these conflicting needs by using sensor networks to gather environmental information for properly allocating resources to cropland when and where these resources are needed. Drones and satellites can capture much information but are not ideal for deducing humidity and soil moisture levels. For optimum data collection, moisture sensing devices must be installed at ground level at high density. If the sensors are not biodegradable, they must be collected at the end of their service life, which can be labor-intensive, rendering them impractical. Achieving both electronic functionality and biodegradability in one technology is the goal of the present work.

Fig. 2
a) Components and configuration of the degradable soil moisture sensor. b) Sn used as a conductive material is unlikely to cause plant damage even if it remains in the soil unlike silver (Ag) and copper (Cu).

Fig. 3
The developed sensor is mostly decomposed by microorganisms in the soil, and the residual components are also environmentally friendly

"Our system comprises several sensors, a wireless power supply, and a thermal camera for acquiring and transmitting sensing and location data," explains Takaaki Kasuga, lead author of the study. "The in-soil components are largely ecofriendly; composed of a nanopaper substrate, a natural wax protective coating, a carbon heater, and tin conductive lines."

The basis of the technology is that the efficiency of wireless power transmission to the sensor corresponds to the temperature of the sensor's heater and the moisture content of the surrounding soil. For example, at optimized sensor positions and angles on smooth soil, increasing the soil moisture content from 5% to 30% decreases the transmission efficiency from ~46% to ~3%. A thermal camera then captures images of the area to simultaneously collect soil moisture-content data and sensor location data. At the end of the crop season, the sensors can be tilled into the soil for biodegradation.

"We have successfully visualized areas of soil moisture deficit by using 12 sensors in a 0.4-meter by 0.6-meter demonstration field," says Kasuga. "Thus, our system works at the high sensor densities needed for precision agriculture."

This work has the potential to optimize precision agriculture for an increasingly resource-limited world. Maximizing the performance of the researchers' technology under nonideal conditions (such as irregular sensor positions and angles on rough soil), and possibly for other soil environmental metrics besides soil moisture levels, might facilitate widespread adoption by the global agricultural community.

About Osaka University

Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.

Website: https://resou.osaka-u.ac.jp/en

Published: 17 Oct 2023

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Global Strategy Unit

1-1 Yamadaoka, Suita,Osaka 565-0871, Japan

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Japan Society for the Promotion of Science, Japan Science and Technology Agency, Shorai Foundation for Science and Technology