A simple wet chemical extraction procedure to characterize soil organic matter (SOM) .2. Reproducibility and verification

In a previous communication in this journal, a fractionation scheme of soil organic matter (SOM) was presented (1). The goal of this paper is to discuss the reproducibility and verification of this procedure with an expanded data set of 150 samples. Litter compound analysis (LCA) is appropriate to detect small differences in the decomposition degree at a quantitative level which are not detectable with SOM morphology. In contrast, humic compound analysis (HCA) is not appropriate to characterize SOM with regard to quantitative data, because the detected carbon (C) (C recovery rate <800 mg/g TOC) reflects only parts of the total SOM. In addition selected, SOM fractions are determined with both extraction procedures. When counting C as polysaccharides in the LCA and as fulvic acid in the HCA, this gives recovery rates of much more than 100% (>1,200 mg/g TOC). These errors induce both an under- or an over-estimation of C within the combination of the litter and humic compound analyses (LCA+HCA) and the conversion to 100% should not be used. Because of the method problems and limited chemical information provided with HCA, we propose using LCA and additional analytical instuments (e.g. NMR, pyrolysis) to further characterize structures in the non-litter substances of the SOM pool.