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.

This study was conducted to determine the relationship between the soil organic carbon (OC) content and selected soil properties such as pH(H₂O), 1 M KCl-extractable aluminum (KCl-Al, exchangeable Al), pyrophosphate-extractable Al and Fe (Al_p and Fe_p, humus complexed Al and Fe), and acid oxalate-extractable Si (Si_o, Si in allophanic minerals) in 293 A horizons from the Tohoku University World Andosol Database. A path analysis was used to examine the direct effects and indirect effects of the soil properties on the OC content. The path analysis showed that a high correlative coefficient between the OC content and Al_p (r = 0.69, P < 0.01) was mainly explained by the direct effect of Al_p (0.52, P < 0.01) on the OC content. Strong correlations between OC and KCl-Al (r = 0.60, P < 0.01) or pH(H₂O) (r = -0.58, P < 0.01) were due not only to the direct effect (0.21 and -0.27, respectively, P < 0.01), but also to the indirect effects of other properties, especially that of Al_p. Thus, it is considered that, in the humus horizons of the Andosols, the Al-humus complexation mainly contributes to the OC accumulation, and the low soil pH values and Al toxicity partly relate to the humus reservation by depressing the microbial activity.

　一般社団法人　日本土壌肥料学会では，学校教育や社会教育の中で，陸上生態系の基盤である土壌に関する環境教育の不十分さが危惧されることから，土壌の重要性を啓発するために，全国10 箇所の自然観察の森において，土壌観察会をおこなってきた。しかしながら自然観察の森の土壌の性質は調べられていない。

　本研究では，自然観察の森の土壌の断面調査および一般化学性分析をおこない，土壌の特徴を調べ，分類をおこなった。

　その結果，自然観察の森の土壌は，褐色森林土，黒ぼく土，赤黄色土が分布しており，ポドゾル以外の日本の主な森林土壌が観察可能なことが明らかとなった。