Optical Sensing of Nitrogen, Phosphorus and Potassium: A Spectrophotometrical Approach Toward Smart Nutrient Deployment

Monteiro-Silva Monteiro-Silva,Martins Martins,Jorge Jorge

doi:10.3390/chemosensors7040051

Monteiro-Silva Monteiro-Silva, Martins Martins + Show 1 more

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https://doi.org/10.3390/chemosensors7040051

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Abstract

The feasibility of a compact, modular sensing system able to quantify the presence of nitrogen, phosphorus and potassium (NPK) in nutrient-containing fertilizer water was investigated. Direct UV-Vis spectroscopy combined with optical fibers were employed to design modular compact sensing systems able to record absorption spectra of nutrient solutions resulting from local producer samples. N, P, and K spectral interference was studied by mixtures of commercial fertilizer solutions to simulate real conditions in hydroponic productions. This study demonstrates that the use of bands for the quantification of nitrogen with linear or logarithmic regression models does not produce analytical grade calibrations. Furthermore, multivariate regression models, i.e., Partial Least Squares (PLS), which consider specimens interference, perform poorly for low absorbance nutrients. The high interference present in the spectra has proven to be solved by an innovative self-learning artificial intelligence algorithm that is able to find interference modes among a spectral database to produce consistent predictions. By correctly modeling the existing interferences, analytical grade quantification of N, P, and K has proven feasible. The results of this work open the possibility of real-time NPK monitoring in Micro-Irrigation Systems.

Highlights

Since the 1950s, the use of fertilizers has changed agriculture productivity and its industry has grown significantly [1]
We aimed to demonstrate the viability of measuring NPK using spectroscopy, overcoming the inherent difficulties usually associated with real nutrient sample assessment: fertilizers constituents’
Results show that the direct quantification of nitrogen, phosphorus and potassium (NPK) in Results show that the direct quantification of nitrogen, phosphorus and potassium (NPK) in fertilizers using UV-Vis spectroscopy is only feasible if interference modes between all specimens fertilizers using UV-Vis spectroscopy is only feasible if interference modes between all specimens are are considered

Summary

Introduction

Since the 1950s, the use of fertilizers has changed agriculture productivity and its industry has grown significantly [1]. The global liquid fertilizer industry was estimated to be worth 11.2 billion. Several factors have helped this growth: development of micro-economies, globalization of the economy and world markets, and technological evolution toward mechanization and automation. In the latter category, development of Micro-Irrigation Systems (MIS) are today key agricultural technologies [3] as they allow farmers and growers to perform precision irrigation in small quantities, with spatial accuracy and the correct amount of nutrients, leading to better nutrient distribution efficiency and crop yield. Several case-studies [5,6,7], guidelines [8,9], and papers [10,11,12,13] are available, approaching the subject of technology in crop management

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