Abstract
In this paper, we demonstrate the suitability, sensitivity, and precision of low-cost and easy-to-use ion-selective electrodes (ISEs) for concurrent detection of NH4 + and NO3 - in soil and water by technical and non-technical end-users to enable efficient soil and water management exposed to chronic reactive nitrogen loading. We developed a simplified methodology for sample preparation followed by the demonstration of an analytical methodology resulting in improvements of sensitivity and precision of ISEs. Herein, we compared and contrasted ISEs with traditional laboratory-based technique such as Flow Injection Analysis (FIA) and portable colorimetric assay followed by comparisons of linear regression and Bayesian nonlinear calibration approaches applied on both direct potentiometry and standard addition modes of analysis in terms of in-field applications and improvement of sensitivity and precision. The ISEs were validated for sensing on a range of ambient soil and water samples representing a range of NH4 + and NO3 - concentrations from pristine to excessive saturation conditions. Herein developed methodology showed excellent agreement with lab-based and portable analytical techniques while demonstrating improvements in precision and sensitivity analysis illustrated by a decrease in confidence intervals by 50-60%. We also demonstrated the utilization of the entire ISE response curve thus removing the biases originating from linear approximation which is often currently employed. Therefore, we show that ISEs are robust yet low cost and an easy to use technology that can enable high-frequency measurement of mineral N and help to improve our understanding of N transformation processes as influenced by soil management, fertilization, land use, and climate change.
Highlights
Of great concern is the increase in anthropogenic inputs of reactive nitrogen (Nr: oxidized and reduced forms of nitrogen) arising from the uses of nitrogen fertilizers, organic manures, sewage wastes, and fossil fuel
It is noteworthy that the limit of detections (LODs) obtained according to the classical IUPAC definition for ion-selective electrodes (ISEs) were estimated as 5.3 × 10-6 M (0.09 ppm) for NH4+ and 3.1 × 10-6 M (0.2 ppm) for NO3
We demonstrated that the multisensor array allowed concurrent determination of NH4+, and NO3- leading to drastically simplified handling protocols
Summary
Of great concern is the increase in anthropogenic inputs of reactive nitrogen (Nr: oxidized and reduced forms of nitrogen) arising from the uses of nitrogen fertilizers, organic manures, sewage wastes, and fossil fuel Their excessive use has more than doubled the input of Nr into terrestrial landscapes alone.[1,2,3] While boosting crop production, excessive N fertilizer use in agriculture poses significant risks of losses of Nr into the air and water.[4,5,6] Nr loss pathways in soils involve nitrate leaching, nitrate and ammonium run-off into surface water, volatilization of ammonia, and emission of nitric oxide as well as nitrous oxide into the air– the latter being a potent greenhouse gas produced through denitrification and nitrification.[7,8,9] Worryingly, the current global nitrogen use efficiency is only up to 45% by crops further enhancing Nr losses.
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