Secondary calcification of paddy soils in southern china: Morphological and substantive characteristics

Secondary calcification processes have been studied in three paddy soils (Anthrosols or Aquazems) of southern China. It is shown that the soils’ amendment with lime powder and the periodic ponding of rice paddies with carbonate-rich water lead to the considerable transformation of the initial soils. The general properties of these soils and their morphological, micromorphological, and mineralogical features have been analyzed, and isotopic studies of the carbonate concentrations have been performed. The studied soils differ in the degree of their secondary calcification. The presence of lithogenic and pedogenic carbonates in the soils has been proved. Among the pedogenic carbonates, younger and older concentrations can be distinguished. The major feature of the carbonate concentrations in the studied soils is the coprecipitation of calcium and iron in the clay soil matrix. In general, the studied soil profiles display the initial stages of calcification. At the same time, there are certain analogies between the process of calcification in the paddy soils and the formation of thick accumulative calcareous crusts in some soils of northeastern China.