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Soils are an important component in the biogeochemical cycle of carbon, storing about four times more carbon that biomass plants and nearly three times more than the atmosphere. Moreover, the carbon content is directly related on the capacity of water retention, fertility, among others properties. Thus, soil carbon quantification in field conditions is an important challenge related to carbon cycle and global climate changes. Nowadays, Laser Induced Breakdown Spectroscopy (LIBS) has beeb applied to qualitative elemental analyses without previous treatment of samples and the results are obtained quickly. New optical technologies made possible portable LIBS systems and now, the great expectation is the development of methods that make possible quantitative analysis with LIBS. LIBS is a technique that employs a sampling by laser ablation and subsequent excitation of atoms present in induced microplasma during the ablation. The goal of this research was the development of methodology to estimate carbon in soil samples and evaluate the performance of portable LIBS systems for analysis in the field. Thirty six soil samples of Brazilian Cerrado region (Argisoil) were used. To evaluate the effect of heterogeneity, it was used samples that were grounding in a cryogenic ground and samples if not grounded. In order to study a better way to estimate the carbon content in the soil, four different methodologies were employed using the bench LIBS system and only one methodology for the portable LIBS system. For both LIBS systems was needed to do corrections in the background of obtained spectra. The carbon line at 193.03 nm was used because it does not present an interference of iron. The technique of thermal analysis known as TOC (Total Organic Carbon) was used as reference to calibrate the systems. Using the bench LIBS system have been adjusted models based on simple linear regression and exponential growth to estimate the carbon content in the samples. For portable LIBS system were used models based on simple linear regression and multiple linear regression. The best methodology used to the bench LIBS system was using the maximum of laser energy (50 mJ) and the largest shots count (10 shots count) and simple linear regression model showed a better fit. There was no difference between the data obtained from the grounded and not grounded samples. For the portable LIBS system multiple linear regression showed a better result because was select the best variable. Thus, it appears that LIBS systems are useful tools to perform quantitative estimates and could be used to build inventories of carbon in the soil that are important to environmental areas with the focus on carbon sequestration, global climate change, assessment the management of soils and the effect of wastewater into the soil.

Estudo de uma metodologia para estimar a quantidade de carbono em amostras de solo utilizando espectroscopia de emissão óptica com plasma induzido por laser (LIBS)