Electrochemical Soil Nitrate Sensor for In Situ Real-Time Monitoring

Abstract

Sustainable agriculture is the answer to the rapid rise in food demand which is straining our soil, leading to desertification, food insecurity, and ecosystem imbalance. Sustainable agriculture revolves around having real-time soil health information to allow farmers to make the correct decisions. We present an ion-selective electrode (ISE) electrochemical soil nitrate sensor that utilizes electrochemical impedance spectroscopy (EIS) for direct real-time continuous soil nitrate measurement without any soil pretreatment. The sensor functionality, performance, and in-soil dynamics have been reported. The ion-selective electrode (ISE) is applied by drop casting onto the working electrode. The study was conducted on three different soil textures (clay, sandy loam, and loamy clay) to cover the range of the soil texture triangle. The non-linear regression models showed a nitrate-dependent response with R2 > 0.97 for the various soil textures in the nitrate range of 5–512 ppm. The validation of the sensor showed an error rate of less than 20% between the measured nitrate and reference nitrate for multiple different soil textures, including ones that were not used in the calibration of the sensor. A 7-day-long in situ soil study showed the capability of the sensor to measure soil nitrate in a temporally dynamic manner with an error rate of less than 20%.

Underground Ink: Printed Electronics Enabling Electrochemical Sensing in Soil

“…Printed EIS sensors can be easily interfaced, however, with integrated electronic units, enabling the assembly of a compact measurement platform that includes a microcontroller, SD card, battery, and potentiostat. Eldeeb et al utilized a screen-printed planar three-electrode sensor platform to conduct in situ EIS tests in soil, as shown in Figure 6 [81,82]. Customized films can be applied to the working electrode for different analytes.…”

“…Customized films can be applied to the working electrode for different analytes. Eldeeb et al drop-casted a nitrate ion-selective film on the working electrode, enabling the detection of nitrate in sandy loam, clay, and loamy clay soil in the range of 6−64 ppm with a decrease of approximately 900 Ω, 650 Ω, and 900 Ω per 5 ppm increase, respectively [81]. The working electrode can also be coated with a mixture of alizarin and Nafion to detect the soil pH value, demonstrating a sensitivity of 258.5 Ω/pH in clay soil [82].…”

“…Traditional data acquisition systems used for the characterization of sensors typically involve wired connections or manual readings using LCR meters or similar equipment [48,97]. For a more seamless solution, microcontrollers, such as Arduino [81,98,99], ESP32 [100], or Raspberry Pi [101], can be directly incorporated into sensor designs to process and transmit data. Printed electronics offer flexible and customizable solutions for integrating signal conditioning components directly onto sensor substrates, which reduces the need for external circuitry and enhances overall system integration.…”

Advancement of Remote Sensing for Soil Measurements and Applications: A Comprehensive Review

“…The results show that soil testing with electrochemical sensor is very effective and accurately and quickly detected for experimentation [158] Soil nutrient Electrochemical sensor A nitrate sensor that uses electrochemical impedance spectroscopy with ion-selective electrode allows direct and continuous soil nitrate monitoring without pre-treatment Soil nitrate can be measured dynamically with <20% error in a 7-day experiment using the sensor [85] Soil nutrients Optical Sensor methods Test optical methods for detecting soil nutrients with a portable sensor that senses nutrients in dry soil samples without extensive preparation.…”

Espial: Electrochemical Soil pH Sensor for In Situ Real-Time Monitoring

“…They all require the mixing of soil with a CaCl 2 solution or KCl buffers prior to measuring. Recently, researchers started looking at electrochemistry to measure various soil parameters [23][24][25]. This work showcases the first-of-its-kind real-time continuous in situ soil pH measurement through the use of alizarin, a quinone that showed the highest accuracy in measuring pH in unbuffered media [19,24].…”