Physico-chemical characteristics of the soils developed from alluvial deposits on Chongming Island in Shanghai, China

Characterization of the physico-chemical properties of the soils collected from Chongming Island in Shanghai, China, which is the largest alluvial island with a total area of about 1,070 km(2) in the world, has been conducted in order to investigate the current status of agricultural soils, with special reference to the effect of alluvial deposits on the development and utilization of, the soils. The experimental results indicated that the soils from Qianjin Farm (QJ) and Dongfeng Farm (DF) on this Island were markedly influenced by the marine deposits and the saline groundwater and showed higher Na+ and Cl- contents, whereas the soils from Xinhai Farm (XII), Luhua Town (1,11), and Jiangkou Town (JK) were significantly affected by the fluvial deposits and showed higher CO32-, HCO3-, and SO42- contents. The basic cations in the topsoils had been evidently washed out, and hence their contents had decreased to a lower level in the soils (DF, XH, and LH) under rice cultivation for more than 10 years. A larger amount of organic matter and other available nutrients accumulated in the paddy soils (DF, XH, and LH) than in the upland soils (QJ and JK). The groundwater under the sampling sites showed a higher salinity, which contributed considerably to the salinization of the coastal soils. The soils from the upland fields (QJ and JK) showed a lower salt content in the subsoils than in the topsoils, in contrast to the paddy soils. The results of this experiment also indicated that the fluvial deposits tended to contribute to the formation of a sandier soil texture than the marine deposits.