Evaluation of Laser-Induced Breakdown Spectroscopy (LIBS) as a Measurement Technique for Evaluation of Total Elemental Concentration in Soils

Online analysis of nutrients in soil would be beneficial in soil and agronomic sciences as it could lead to real-time adjustment of the level of nutrients in soils. Laser-induced breakdown spectroscopy (LIBS) yields a real-time signal that could be correlated with the total elemental concentration in soils, and, hopefully, to the available fraction of the element in soils. As a first step in developing a technique for the real-time evaluation of the nutrient concentration in soils, in this study LIBS was applied to the evaluation of total element concentrations in mixtures of soils and fertilizers. Two fertilizers were mixed with soil in several concentrations, and loose powder samples of these mixtures were analyzed using LIBS. Calibration curves for three macroelements, calcium (Ca), magnesium (Mg), and phosphorus (P), and two microelements, iron (Fe) and sodium (Na), in the samples allowed determination of detection and quantification limits for total elements in soils. The correlation coefficients (r(2)) between total element concentrations and the LIBS signal were above 0.85 for all elements; however, we note that Ca showed evidence of self-absorption. The quantification limits were below typical total element concentration in soils; however, matrix effects demanded one calibration curve for each element and for each soil/fertilizer mixture.