Three types of paddy soil were sampled from different three sites of Zhejiang Province.Huangson rice field soil was developed from fluvo aquic soil matrix,old Huangjin rice field soil from the Quaternary red calay soil matrix and Qingzi rice field soil from coastal saline soil matrix,which were not applied any fertilizer.The bigger stones and larger fiber residues of plant were removed in the soil samples.15 kg of each soil sample was put into 13L plastic barrel and immerged over with water.Three plast...