Investigation of the Moisture Effects on Printed Nitrate-Selective Potentiometric Sensors for Direct Soil Monitoring

As the demand for sustainable and efficient agriculture grows, there is an increasing need for reliable and cost-effective methods to monitor soil nutrient levels. Printed nitrate-selective potentiometric sensors have emerged as promising tools for in situ soil monitoring, offering real-time and continuous measurements of nitrate concentrations. However, the performance and longevity of these sensors can be influenced by environmental factors, particularly moisture content in the soil. This work presents the effects of soil moisture level on the functionality and accuracy of printed nitrate-selective potentiometric sensors, with the goal of enhancing their performance and reliability for soil nutrient monitoring applications.<br/> Building upon our prior research, we successfully manufactured inkjet printed potentiometric sensors that are specifically tailored for the detection of the nitrate in soil. The printed sensors contain two electrodes, the reference (RE) and ion-selective electrode (ISE). The ISE is covered by a drop-casted nitrate-selective membrane, which only allows the ion of interest in soil, nitrate in this work, interacting with electrode. This interaction generates a measurable potential difference across the RE and ISE, which can be correlated to the nitrate concentration in the soil.<br/> To measure nitrate contents in moist soil environments, a porous hydrophilic polyvinylidene fluoride (PVDF) film is introduced into the potentiometric sensor. The PVDF shields the electrodes from charged soil particles, while allowing the passage of water. This feature ensures effective operation and provides protection from the soil environments, enabling direct sensing of nitrate in a medium that is similar to in aqueous solutions. The printed potentiometric sensors exhibit sensitivities ranging from sensitivities 45 - 50 mV/dec.To evaluate the performance of the printed potentiometric sensors under realistic conditions, the sensors are testes in two common crop field soil texture classes: sandy soil and silt loam soil. These soil types were chosen to represent practical scenarios encountered in agricultural settings. A range of nitrate concentrations, representative of typical agricultural scenarios, are applied to the sensors, and the response of the sensors is recorded under different moisture conditions.<br/> This study will provide valuable insights into the impact of moisture on the performance of printed sensors and contribute to the development of robust and moisture-tolerant sensor designs for accurate soil nutrient monitoring in agricultural systems. By understanding the impact of moisture on sensor performance and developing moisture-tolerant designs, this research contributes to the development of robust and reliable real-time sensing systems for precision agriculture. This research holds significant potential to advance the field of precision agriculture, enabling farmers to optimize fertilizer management practices, reduce environmental impacts, and optimize crop yields in a sustainable manner.