Relationship of Soil Organic Matter and the Stability of Soil Carbon

The formation and decomposition of soil organic carbon (SOC) is important due to the impact on atmospheric CO₂ concentration.  The functions of SOC depend on both its quantity and stability of soil organic matter (SOM).  The stability of SOM can be defined by how easily SOC can be mineralized to CO₂. Humic substances in soil can be regarded as stabilized SOM, i.e., low-quality resistant, hardly biodegradable SOM and not capable of producing CO₂.  Various estimation techniques have been used to characterize SOM stability. In this study, total organic carbon (TOC) for humic substance extracted from soil, the fraction of hot-water extractable organic carbon (HWEOC), and the soil itself were analyzed and results were compared to determine the relationships among them. Results between SOM and SOC showed that both have strong linear relationships with the slope of 0.580 and high correlation over 0.99, which indicated that 58% of SOM is SOC. In the comparison between SOM and HWEOC, the values of HWEOC/SOM were lied in 5~6%, which means that that much of the percentage of SOM fraction can be extracted by hot water—about 8.6~10.3% of SOC might be labile fraction. Results on the HWEOC and humic substance showed relationship that HWEOC = 0.536 OC in humic substance – 0.0042, with somewhat scattered data distribution, which has correlation coefficient of 0.6938.