Effects of Dry and Wet Climates on the Content and Components of Organic Matter in Paddy Soils in Tropical Region

Key words: 
• humidity /
• paddy soil /
• organic matter /
• physical fractionation

Abstract: Paddy soils were sampled from Qiongzhong county and Dongfang city in Hainan Province,where the humidity was highly different,,to analyze the influences of the dry and wet climatic conditions in tropical region of China on organic matter and its components in the paddy soils. The relationships between the organic matter and its components,and the organic matter sequestration potential were investigated by using the method for physical fractionation. Dry and wet climatic conditions affected the content of soil organic matter and its components. The paddy soils contained higher organic matter and components in the humid climatic region than in the semiarid climatic region. The organic matter content showed a significantly positive linear correlation with the light fraction organic matter（ LFOM） content and the heavy fraction organic matter（ HFOM） content,and the HFOM content was also significantly positively correlated with fulvic acid（ FA）. Paddy soils had higher potential of organic matter fixation in the semiarid region than in the humid region. Humid climate is conducive to the formation of HFOM. The soil humus in the tropical region had weak combining ability and contained mostly FA.Measures should be taken to increase the potential of paddy soils in carbon sequestration in the dry tropical region.