Impacts of Land Use on Variations of Soil 14C-Age and Determination of Organic Matter Quality by FTIR Spectrometry

Soil organic carbon (SOC) plays an important role in the global carbon cycle, and study of dynamics concerns the recent development of nuclear industry. Physical fractionation, radiocarbon dating and FTIR spectrometry methods are among the most important methods for determining carbon dynamics and thereby the magnitude of soil carbon response to land uses. In this study, methodologies of carbon dating and FTIR spectrometry were used to characterize impacts of land use on mean residence times and quality (functional groups) of soil organic carbon based on physical fractionation methods in three land uses including deciduous, coniferous forests and rangelands. The FTIR spectra showed that higher aromatic carbon proportion and its lower decay rate of organic matter in coniferous forest have caused more SOC content. Free and intra-aggregates particulate organic matters (POM) have been recognized as criterion indices for deciduous forest use. Compared to the other land uses, the higher aliphatic to aromatic carbon ratios were obtained in litter and intra-aggregates POM of deciduous forest. The highest14C age in both forest land uses (deciduous and coniferous) was measured in the Bhorizon, while in the rangeland occurred at the A horizon. Aromatic functional groups as well as 14C age are suitable parameters for homification processes.