An In-Situ Soil Nitrate Nitrogen Detection System based onIon-selective Electrode

摘要

Nitrogen is one of the macronutrients in soil, which is essential to plant growth and crop production. Nitrate nitrogen (NO3-N), naturally converted from mineralization and nitrification of organic nitrogen, is an important indicator of nitrogen levelin the soil. Recently, the migration movement of soil NOs-N has been investigated extensively for the increasing awareness offood and environment safety. Ion-selective electrodes (ISEs) has been widely applied for the routine analysis of soil NO3-N because of its simple instrumentation, fast response, and easy miniaturization. However, its performance was reported to be unsatisfactory in most of the in-field detections. In this paper, an in-situ soil NO3-N monitoring system was developed based on Thermo ISE. Soil percolate extraction was obtained through the porous ceramic cylinder with pneumatic pumps for the perception ofpressure control. Once installed, pneumatic pressure was evaluated according to the volume of extracted percolate. A solid-state NO3- ISE was integrated inside of the percolate extraction container. Effects of the installation position of ceramics were discussed at the mass soil moisture level of 20%. Comparisons were made between the detection of percolate in the standard method and based on the ISE method The test stand was filled with sandy, loamy soil, which was premixed thoroughly to get a uniform condition of nutrient, texture. According to the test results, the optimized pneumatic pressure was decided as -90 mbar. Under theoptimized operation pressure, unit amounts of collected soil percolates were (28.0±4.2), (28.3±6.6), and (22.0±1.6) mL/h, when ceramic cylinders were positioned at a depth of 0.25, 0.5, and 0.8, respectively. Compared with the standard spectrometricmethod, ISE produced an acceptable accuracy with the absolute error of 0.02-23.02 ppm in the detection ofpercolate samples. ISE demonstrated promising perspective on in-site dynamic soil monitoring.