Use of near-infrared reflectance spectroscopy in soil analysis

This paper presents a literature review on the development of near infrared reflectance spectroscopy for soil analysis and the contribution of this technique to the evaluation of soil fertility analysis. This technique is used to estimate the chemical composition of soil samples on the basis of their absorption properties. It is therefore an indirect method of measurement, which requires a calibration phase for the prediction of these properties. NIR spectroscopy offers many advantages compared to reference analysis: it is known to be a physical, non-destructive, rapid, reproducible and low cost method. Often employed in other analytical domains, such as agro-food, NIR spectroscopy has, however, seldom been used in soil characterization, due to the complexity of the soil matrix. Thanks to the development of chemometric methods, numerous studies have recently been conducted to evaluate the feasibility of the application of the technique in soil analysis. Most authors conclude that NIR spectroscopy is promising; however, to date, use of the technique has not spread to routine laboratories. The paper is organized as follows. Firstly, we provide an overview of the NIR spectroscopy technique and related chemometric methods. Secondly, we describe the soil characteristics that can be predicted using this technique. Finally, we detail examples of results that have been obtained through the use of the technique, mainly in the determination of clay and organic carbon content, and of cation exchange capacity.