Genetic Characteristics And Classification In Chinese Soil Taxonomy Of Paddy Soil In Changsha

In order to lay a solid foundation for the soil classification and investigation, to protect and utilize the cultivated land effectively, the soil samples of different horizon in 12 typical soil profiles of paddy soil derived from 5 soil parent materials in Changsha were collected, identified and classified, and their soil texture, organic matter and iron oxide in different types were analyzed. The main results are as follows:(1) Based on the advances of Chinese Soil Taxonomy,12 typical soil profiles of paddy soil derived from 5 parent materials (paddy soil derived from granite, quaternary red clays, purple stone area, slate and sediment) were chosen to establish preliminarily the relevant soil series in Changsha. The 12 typical soil profiles of paddy soil could be classified into 3 groups,3 subgroups,9 families and 12 series.(2) The soil texture of paddy soil from different soil parent material differed dramatically in vertical direction of profile distribution. The clay content was higher in the subsoil and subsurface soil layer. The clay content went down as follow: Sediment> Quaternary red clays> Purple stone area> Slate> Granite.(3) The contents of organic matter of paddy soil from different soil parent material of in Changsha went down as follow:Slate> Sediment> Purple stone area> Quaternary red clays> Granite. The contents of organic matter decreased with the increasing soil depth of the 5 soil parent material, topsoil layer had the highest content of organic matter, whereas the below layers showed relatively lower content of organic matter. The contents of organic matter in vertical direction went down as follow:Topsoil layer> Subsoil layer> Subsurface soil layer.(4) The highest contents of total iron of paddy soil were sediment and the lowest were granite. The contents of free iron oxide went down as follow:Quaternary red clays> Purple stone area> Granite> Slate> Sediment. The contents of amorphous iron oxide went down as follow:Slate> Sediment> Granite> Purple stone area> Quaternary red clays.(5) The profile distribution of total iron of paddy soil from different soil parent material was the same as free iron oxide generally, they increased with the increasing soil depth of the 5 soil parent material, and the topsoil layer had the lowest content.There were significant positive correlation between free iron oxide and total iron with the same soil parent material. The content of amorphous iron oxide decreased with the increasing soil depth of the five soil parent material, and it showed that no correlation with free iron oxide and total iron.