Minimalizing Non-point Source Pollution Using a Cooperative Ion-Selective Electrode System for Estimating Nitrate Nitrogen in Soil
Rui Su, Junfeng Wu, Jiandong Hu, Liuzheng Ma, Shakeel Ahmed, Yanyan Zhang, Mukhtar Iderawumi Abdulraheem, Zephania Birech, Linze Li, Can Li, Wentao Wei
Abstract
Nitrate nitrogen ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ1"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N) in the soil is one of the important nutrients for growing crops. During the period of precipitation or irrigation, an excessive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ2"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N readily causes its leaching or runoff from the soil surface to rivers due to inaccurate fertilization and water management, leading to non-point source pollution. In general, the measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ3"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N relies upon the laboratory-based absorbance, which is often time-consuming, therefore not suitable for the rapid measurements in the field directly. Ion-selective electrodes (ISEs) support the possibility of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ4"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N measurement by measuring the nitrate ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ5"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> ) ions in soil quickly and accurately due to the high water solubility and mobility of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ6"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> ions. However, such a method suffers from a complicated calibration to remove the influences caused by both temperature and other ions in the measured solution, thus limiting field use. In this study, a kind of all-solid ISE system combined with a temperature sensor and a pH electrode is proposed to automatically measure the concentrations of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ7"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N. In this study, a soil water content calibration function was established, which significantly reduces a relative error (RE) by 13.09%. The experimental results showed that the stabilization time of this electrode system was less than 15 s with a slope of −51.63 mV/decade in the linear range of 10 –5 –10 –2.2 mol/L. Both the limit of detection of 0.5 ppm of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ8"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N and a relative SD of less than 3% were obtained together with the recovery rate of 90–110%. Compared with the UV-Vis spectroscopy method, a correlation coefficient ( R 2 ) of 0.9952 was obtained. The performances of this all-solid ISE system are satisfied for measuring the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="INEQ9"><mml:msubsup><mml:mtext>NO</mml:mtext><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> -N in the field.