Determination of Soil Organic Matter Features of Extractable Fractions Using Capillary Electrophoresis: An Organic Matter Stabilization Study in a Carbon-14-Labeled Long-Term Field Experiment

Insights into the pathways of soil organic matter (SOM) turnover and its stabilization are important in soil science because soil fertility and quality are connected with the amount and quality of the formed SOM pool. Capillary electrophoresis (CE) is a valuable tool to determine the degree of SOM stabilization because it is based on a separation principle (separation of charged molecules in a very strong electric field), which is complementary to most other applied techniques in SOM analyses (e. g., pyrolysis gas chromatography-mass spectrometry [GC-MS], spectroscopic methods, and elemental analyses). The first part of this chapter reviews the current status on application of CE in SOM studies. The second part is a case study in which the potential of CE is evaluated as a method to detect SOM stabilization in a well-investigated C-14-labeled long-term field experiment established in 1967. Referring to a time sequence in the investigated permanent bare fallow (BF) plot, in the case study, we observed four electrophoretic signals that significantly increased over time. Furthermore, extracted SOM from silt-and clay-sized particles was determined. Many signals in the electropherograms (two humps and six peaks) significantly reflected differences in SOM, which were attributed to various cropping systems or different particle size fractions. These results suggest that the signal intensities of hump 2 and the peaks 2, 4, and 6 represent subfractions of SOM that are clearly related to increasing SOM stabilization; hump 1 apparently included a considerable labile proportion of SOM. Based on the very consistent data for hump 2 and the peaks 2, 4, and 6, we conclude that CE is a highly applicable tool to investigate the stabilization of SOM in soil systems.