Estimation of soil organic matter composition according to a simple thermoanalytical approach

Abstract

The release of carbon and water from soil organic matter (SOM) was determined with a LECO analyzer (RC‐412) and compared to weight loss data obtained by analysis of soils with a normal thermogravimetric method, SOM fractions obtained by wet chemical extractions and SOM subunits of carbon‐13 NMR spectroscopy of bulk soil samples. Four soil horizons were used for the analysis with the LECO analyzer. Wet chemical data as well as NMR spectra show a specific SOM composition of the soil horizons. The thermoanalytical analysis allows a quantitative separation of carbon and water release, and the thermal diagrams confirm the specificity of the SOM in the different soil horizons. The heating rate in the LECO analyzer with a low temperature progression improves the resolution of the carbon release in comparison to the continuous temperature increase (105°C to l,000°C) of at a speed of 70°C min^‐1. The thermostability index Rp can be used to characterize the humification level and provides a semiquantitative carbohydrate estimate in the SOM fraction. The obtained C/O and the C/H ratios are perhaps simple parameters to observe changes in carbon (C), oxygen (O), and hydrogen (H) for characterization of turnover processes and humification of organic matter in soil.