THE DISTRIBUTION OF SOIL ORGANIC MATTER AND STUDY OF HUMIC SUBSTANCES CHARACTERISTICS IN AILAO MOUNTAIN

This paper describes a preliminary study on the mineral cycling in a subtropical montane forest, the secondary vegetation succession and the change of soil fertility. Soil organic matter decreases from about 14% to.about 4% in yellow brown earth and from about 7% to about 1% in red earth, according to the order of natural vegetation, secondary vegetation and cultivated-s0il. The ratios of carbon of humic substances to carbon of nonhumic is the lowest in the soil of the natural vegetation, but it is higher in the under layer than surface. However, the ratios are nonsignificant in cultivated land in the same soil profile. Element analysis shows the C/H ratio of humie acid is the lowest in natural vegetation, but it is higher in the under layer than surface in the same soil profile. Functional group analytical results show that there are more acidity, carboxyl group, phenolic OH and C=O in natural vegetation. The number-average molecular weights(Mn) of fulvic acid of yellow brown earth is 714, and its distributional range is from 198-1052. Carbon content is 44% (40.5-51.4%). Hydrogen content is 4.88%(3.74-5.45%). Nitrogen content is 2.2%. Oxygen and sulfur content is 48.92%.E₄/E₆ ratio is 6.84(4.16-8.56).