Evolution of soil chemical properties in the past 50 years in the Tai Lake Region, China

The Tai Lake Region (TLR) is traditionally an ecologically sustainable agricultural area due to the intensive application of traditional organic fertilizer. However in the past 50 years, agricultural management practices such as fertilizer usage and cropping systems changed this situation. In order to investigate how these changes affected soil chemical properties and ultimately the sustainability of agriculture production, a case study was conducted in Taicang County in the TLR. It was found that soil organic carbon (SOC) content significantly decreased from 22.8 g kg−1 in 1959 to 12.9 g kg−1 in 1981 while soil total nitrogen (TN) increased significantly from 1.2 g kg−1 in 1959 to 1.6 g kg−1 in 1981 due to the application of mineral fertilizer especially N fertilizer nearly entirely replacing of traditional organic fertilizer, and then both slightly increased to 14.0 g kg−1 and 1.7 g kg−1, respectively in 2004. Soil total phosphorus (TP), total potassium (TK), and available K (AK) contents showed little changes from 1981 to 2004 but soil available P (AP) content increased significantly from 7 mg kg−1 in 1981 to 26 mg kg−1 in 2004. The changes of soil properties from 1959 to 1981 were attributed to the changes of fertilizer usage and the changes of soil properties from 1981 to 2004 were attributed to the changes of cropping systems and fertilizer application, particularly vegetable production which resulted in the significant changes of fertilizer usage.