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

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 degrees C to 1,000 degrees C) of at a speed of 70 degrees 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.