Development of Ion-Selective Electrodes for Detection of Nitrogen-Based Ions Among Soil Nutrients

Recently, analyzing soil nutrients has been vastly emphasized in developing next-generation agriculture based on smart-farm. Remarkably, there is much attention to the on-site and real-time analysis of nutrients inside the soil. As a result, some attempts have been made to achieve this purpose. If it is realized, it enables minimal use of fertilizers and finally reduces overall analysis cost.<br/>Conventional methods for analyzing soil nutrients include colorimetry, spectrophotometry, flame photometry, and atomic spectrometry. However, some of them require pre-processing steps and expensive equipment. Some methods are also challenging because of selectivity, on-site detection, and multiple analysis.<br/>Ion-selective electrode (ISE)-based potentiometry has several advantages compared to the conventional methods. First, it allows minimal pre-treatment steps, especially for the soil sample. Second, it enables cost-effective analysis because it does not require expensive equipment. Third, it has superior selectivity compared to other methods. Fourth, on-site, real-time, and multiple monitoring of soil nutrients effectively works through miniaturization of the measurement part.<br/>Nitrogen (N), phosphorus (P), and potassium (K) are estimated to be essential elements among several soil nutrients. In particular, nitrogen-based ions (ammonium, nitrate, and nitrite) are critical for efficient crop growth. Therefore, developing sensors for accurate and fast analysis of nitrogen-based nutrients is necessary. In this study, several ISEs have been prepared to detect nitrogen-based ions. The membranes of ISEs were optimized by changing the components (matrix, ionophore, plasticizer, and lipophilic additive) and their amounts. The experiments were carried out in a buffer solution, similar to the soil environment. The sensitivity and selectivity of ISEs were intensively investigated and compared with commercial ISEs. Finally, preliminary experiments were performed inside the soil to monitor nitrogen-based ions directly and simultaneously.<br/>This work was carried out with the support of Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ015725032021) Rural Development Administration, Republic of Korea.