Linking thermogravimetric data with soil organic carbon fractions

Different soil fractionation approaches are frequently used to separate soil organic carbon (SOC) pools of different turnover time and shed light on soil carbon dynamics. However, these methods are laborious and time consuming. Thermogravimetry might be an alternative. Previous studies revealed relationships between soil organic matter (SOM), total nitrogen, clay content, and soil respiration and thermogravimetry (TG) data represented by TG indicators (mass loss in 10 °C intervals) and TG fractions (mass loss in larger temperature intervals). In this work, both TG indicators and fractions were correlated with the contents of SOC fractions representing different turnover times. The fractions we used were particulate organic carbon, dissolved organic carbon, organic C in the sand fraction and in stable aggregates, organic C attached to silt and clay particles and a chemically resistant fraction (<63 µm and not oxidizable by NaOCl). Fractionation and thermogravimetry was applied to 144 samples from arable and grassland top- and subsoils. The results revealed that both TG indicators and fractions or their combinations correlated with SOC fractions in grassland topsoils (R2 between = 0.70–0.92, p < 0.001 except for the chemically resistant fraction), while the correlation with SOC fractions in arable soils were significantly lower (R2 between 0.36 and 0.72, p < 0.001). No correlations were observed between TG data and SOC fractions in subsoils of arable and grassland soils. Importantly, most of the correlations were observed in soils in which carbon content correlated with TG indicator between 340 and 350 °C. This TG indicator can be used as a differentiator for the application of developed equations for modeling the functional SOC fractions of different turnover times in various types of soils. Thermogravimetry is not able to replace classical fractionation schemes. However, the results showed that thermogravimetry can be an additional tool to assess SOM quality in different land use systems besides traditional chemical-physical fractionation methods.