Applications of laser‐induced breakdown spectroscopy for soil characterization, part II: Review of elemental analysis and soil classification

Abstract

In‐field soil health assessments, including plant nutrients and toxic elements, are needed and could improve the sustainability of agriculture production. Among the available analytical techniques for these analyses, laser‐induced breakdown spectroscopy (LIBS) has become one of the most promising techniques for real‐time soil analysis at low cost and without the need for reagents. The first part of this two‐part review (Part I, Villas‐Boas, P.R., de Franco, M.A., Gollany, H.T., Martin‐Neto, L. & Milori, D.M.B.P. 2019. Applications of laser‐induced breakdown spectroscopy for soil characterization, Part I: Review of Fundamentals and Chemical and Physical Properties.) in this issue focused on the fundamentals of LIBS for soil analysis and its use for soil chemical and physical characterization. Our objectives in this review article (Part II) are to review (a) the main applications of LIBS in the determination of soil carbon (C), nutrients and toxic elements, spatial elemental mapping, and (b) its use in soil classification. Traditional and more recent techniques will be compared to LIBS, considering their advantages and disadvantages. Laser‐induced breakdown spectroscopy is a promising, versatile technique for detecting many elements in soil samples, requires little or no sample preparation, takes only a few seconds per sample, and has a low cost per sample compared to other techniques. However, overcoming matrix effects is a challenge for LIBS applications in soil analysis, because most studies are conducted with limited changes in the matrix. In spite of the limitation of matrix effects, a typical LIBS system has a limit of detection of 0.3, 0.6, 4, 7, 10, 18, 46 and 89 mg kg−1 for Mo, Cu, Mg, Mn, Fe, Zn, K and Ca, respectively. Laser‐induced breakdown spectroscopy holds potential for real‐time in‐field spatial elemental analysis of soils and practical applications in precision farming with proper calibration. This could lead to immediate diagnoses of contaminated soil and inefficient nutrient supplies and facilitate well‐informed soil management, increasing agricultural production while minimizing environmental impacts. Highlights Laser‐induced breakdown spectroscopy (LIBS) is a fast analytical technique with great potential for elemental mapping of soils. Elemental analyses of soil and plants and soil classification by LIBS are reviewed. Soil and rhizosphere spatial elemental analyses by LIBS are presented. LIBS advantages, limitations and challenges are discussed for soil elemental analysis.

Total Phosphorus Determination in Soils Using Laser-Induced Breakdown Spectroscopy: Evaluating Different Sources of Matrix Effects

“…Particularly in soils, which constitute highly intricate matrices because of their diverse composition and particle size distribution, matrix effects related to sample heterogeneity are a major challenge for LIBS quantitative determination. 22 To minimize general interfering effects originating from the laser–material interaction, and thus enhance LIBS accuracy and precision, different data pre-processing techniques such as normalization, application of sophisticated algorithms, variable selection, ensemble averaging and the use of multivariate calibrations have been introduced. 22,23…”

“…22 To minimize general interfering effects originating from the laser–material interaction, and thus enhance LIBS accuracy and precision, different data pre-processing techniques such as normalization, application of sophisticated algorithms, variable selection, ensemble averaging and the use of multivariate calibrations have been introduced. 22,23…”

“…Phosphorus is one of the most challenging elements among the plant macronutrients for quantification by LIBS due to its weak signal, 22 and only few explorative attempts have been made so far to determine total P in soils. 24–26 Díaz et al.…”

Editorial for Soil chemical, physical and biological interfacial reactions (Commission 2.5, WCSS) special section

“…The two‐part paper by Villas‐Boas, Franco, Martin‐Neto, Gollany, and Milori (2020a,b) describes the principles and applications in soil science of laser‐induced breakdown spectroscopy (LIBS). These papers give a remarkable overview of this technique, which has the advantages of minimal sample preparation, and therefore avoidance of inherent creation of artefacts.…”

“…In the first part, the authors demonstrate the application of LIBS to the characterization of soil pH, the degree of humification of soil organic matter and determination of soil texture. In the second part, Villas‐Boas, Franco, Martin‐Neto, Gollany, and Milori (2020b) review the use of LIBS to assess soil health with a view to improving sustainable agricultural production from measurements of plant nutrients, toxic elements and soil organic carbon content, with capacity to generate more detailed and less expensive soil maps aligned with precision farming demands.…”