SOIL ORGANIC STRUCTURES IN MACRO AND MICROAGGREGATES OF A CULTIVATED BROWN CHERNOZEM

The chemical composition of soil organic binders and their role in agg regate stability is largely unknown. The purpose of this study was to characterize soil organic matter (SOM) in soil macro and microaggregat es by pyrolysis field ionization mass spectrometry (Py-FIMS). In compa rison with a wheat-fallow (WF) rotation, a continuous wheat (CW) syste m stored more organic C, maintained a greater proportion of water stab le macroaggregates > 250 mu m and was characterized by greater molecul ar diversity of SOM. The highest concentration of molecular ions in al l aggregate fractions were carbohydrates, lignin monomers, N compounds , and alkylaromatics (each representing from 9 to 15% of total detecte d molecular ions). Lipids, lignin dimers and sterols were the least ab undant (each representing from 0.3 to 4% of total detected molecular i ons). Linear regression models showed that the proportion of water sta ble macroaggregates was correlated with the concentration of lignin di mers (r = 0.98), sterols (r = 0.94), alkylaromatics (r = 0.94) and lip ids (r = 0.90). Chemical classes of organic compounds were not correla ted with the proportion of water stable microaggregates.