Application of thermogravimetric analysis for the evaluation of organic and inorganic carbon contents in agricultural soils

The presented study focuses on the use of thermogravimetric analysis (TG) for estimating organic (OC) and inorganic carbon (IC) contents in bulk soils of different soil types and agricultural practices. Total carbon (TC) was measured by dry combustion using a total organic carbon (TOC) analyzer. The OC content was obtained as the difference between the TC and IC measurements. Regression equations were developed for relations between the thermal mass losses over various temperature intervals (200-370, 105-550, 110-420, 180-450, 250-440, 250-650, and 200-575 A degrees C) and the OC content to determine the optimal temperature interval for the estimation of OC. The results for IC contents were related to the thermal mass losses at temperatures ranging from 500 to 800 A degrees C. The results demonstrated that the thermal mass losses between 180 and 450 A degrees C were fairly well related to the OC content (R (2) = 0.63), whereas the root-mean-square error of cross-validation (RMSECV) was too high (0.70 % OC). The inclusion of the clay content in the multivariate predictive equation did not importantly lower the RMSECV. By contrast, the thermal mass losses within the interval from 500 to 800 A degrees C were closely related to the IC content determined using the TOC analyzer (R (2) = 0.96), with an acceptable RMSECV of 0.26 %. These results indicate that TG can provide a reliable estimation of the IC content but only rough estimations of the OC content in bulk soils of different types, bedrocks, and land uses.