Evaluation of methods for quantifying organic carbon in mangrove soils from semi-arid region

The objective of this work was to evaluate methods for the determination of soil organic carbon (SOC) in mangrove samples in order to improve economically feasible and precise analytical alternatives Total SOC was quantified through elemental analyzer (EA), considered as the standard method, and compared to (a) a chemical method, based on the oxidation of SOC by potassium dichromate under various conditions: wet and dry samples, with or without external heat source and variations in sulfuric acid concentrations (3.6, 6, 9, and 12 mol L-1); (b) spectral reflectance; and (c) thermogravimetry. Regarding the chemical analysis, the use of dried samples improved the accuracy; external heat sources led to higher interference, with a lower correlation to EA SOC; and the higher correlation with the EA was obtained between a 6 M concentration of sulfuric acid (r = 0.733). The spectral reflectance method showed a low correlation between the EA (-0.492 < r < 0.252) while thermogravimetry showed the largest (r = 0.905). SOC determination through chemical methods using dry samples with a sulfuric acid concentration of 6 M shows the best accuracy. As for the use of the spectral reflectance method in mangrove soils, further studies are needed to investigate the influence of pre- and postprocessing techniques. Thermogravimetry is characterized as the most adequate alternative method for SOC measurement when EA are not available since a correction factor is used (f = 0.27) to convert the soil organic matter content to SOC.