Response of typical paddy soil fertility to long-term cultivation in Taihu Lake Region

The chemical properties of collected soil samples (2004) were compared with that of the Second National Soil Survey (1982) to analyze changes in soil fertility in Wujin, Taihu Lake Region of Jiangsu Province. The results show that of all the six sub-soil varieties of paddy soil collected from 198 sampling sites, the average content of soil total nitrogen, organic matter, available phosphorous and potassium has significantly increased from 1982 to 2004. That of soil pH and CEC (cation exchange capacity) has decreased during the same period. The soil fertility indices of the six paddy sub-soil varieties are largely the same, except for silty and sandy soils. A single factor soil fertility index for all the sub-soil varieties have a similar trend, i.e. available potassium and pH are the lowest single factor soil fertility indices for 1982 and 2004 respectively. White soil has the lowest pH fertility index (1.73). CEC fertility index has decreased from 2.91 ~ 3.0 of the Second National Soil Survey to 2.14 ~ 2.93 of 2004 collected samples. This indicates that the major restricting factor for soil fertility in this region is low soil pH and loss of exchangeable base anions.