Integrated Multifunctional Flexible Sensing System for Soil Nitrate Monitoring

Farmers face an economic burden from rising fertilizer costs and increased pressure to reduce nitrate leaching into groundwater. However, traditional measurements of nitrate flux in soil are labor-intensive and expensive. There is an urgent need to develop an affordable technique that can rapidly and reliably monitor soil nitrate concentration for on-farm practices. This paper presents an integrated flexible soil sensing system capable of detecting temperature, moisture content, and nitrate concentration. The digital temperature sensor operates using temperature-dependent voltage and current characteristics, providing high accuracy of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 0.2^{\circ} \mathrm{C}$</tex>. The moisture sensor utilizes interdigitated electrode capacitance, offering a quick response to moisture changes and covering a broad range of detection. The final component, an inkjet printed electrochemical sensor can directly detect soil nitrate concentration using an ion-selective electrode protected by a polyvinylidene fluoride film. Combining the aforementioned functions, the sensor system collects comprehensive soil parameters related to soil nitrate readings, aiding in the understanding of soil nitrate dynamics. The sensor can provide users continuous soil information enabling them to make informed decisions, ultimately enhancing the efficiency of fertilizer management.