6Nambu K, Yonebayashi K. Role of dissolved organic layer materials in coniferous and broad leaf forests. Soil Sci . Plant Nutr., 1999,45:307 ~ 319
7Van krevelen D W. Graphical-statistical method for the study of structure and reaction processes of coal. Fuel, 1950,29:269 ~ 284
8Yannebaiyashi K, Hattori T. Chemical and biological studies on environmental humic acids I. Composition of elemental and functional groups of humic acids. Soil Sci. Plant Nutr., 1988,34:571 ~ 584
9Tsutsuki K, Kuwatsuka S. Chemical studies on soil humic acids Ⅳ .Amino acid, phenol, and sugar composition in the acid hydrolysable fraction of humic acids. Soil Sci. Plant Nutr., 1979,25:29 ~ 38