2012 年 56 巻 2 号 p. 47-57
The greater part of cultivated lands for crop production is covered by Chernozems and related Kastanozems in Ukraine. Although there were numerous studies regarding soil humus in Ukraine and former USSR, soil organic matter quality evaluated by the humification index and NMR spectroscopy has not been studied in representative Chernozemic zone of Ukraine. In the present study, different Chernozemic soil types under natural grasslands were mainly selected in eastern Ukraine to investigate the properties and characteristics of the soil organic matter dynamics of humic substances in the typical Eurasian Steppe. Under the moist conditions in the north, Typical Chernozems (Chernic-Siltic Chernozems) and Ordinary Chernozems (Chernic-Siltic Chernozems), which could be distinguished by a deep black surface horizon with stronglydeveloped structures and the highly humified Type A humic acids, of which the RF values were remarkably high. Southern Chernozems (Hypocalcic-Siltic Chernozems) and Dark Chestnuts (Calcic-Siltic Chernozems) were the common subtypes under the relatively drier moisture regime, the profiles of which could be characterized by a relatively thin dark-brown or brownish black surface horizon. These soils were also characterized by the Type A humic acids, however, the RF value was less than Typical and Ordinary Chernozems. The aromaticity of humic acids in the surface soils of these Chernozemic soils calculated from 13C NMR spectra were extremely high comparable to that of highly-humified Type A humic acids of Japanese Andisols, suggesting that black carbon might contribute to the highly aromatic and recalcitrant SOM and could be recovered in the chemical fraction defined as humic acids in these black soils. We still need to clarify the impacts of anthropogenic activities and intensive agricultural practices on the soil organic matter quality of humic acids in Chernozemic soils.
