Changes of soil organic matter and nutrients and their relationship with crop yield in high yield farmland

Average crop yield，soil organic matter，soil available nutrients content，application rates of chemical fertilizers during 1982 to 1998 in Huantai County，Shandong Province were analyzed．Huaitai County is famous for its high unit yield，i．e．15 tons of grain can be produced on 1 hectare of farmland annually．The study indicates that soil organic matter(SOM) has been increasing from 1982 to 1998，and the increase range decreases with the widespread of crop straw return technology in Huantai County．In 1998，SOM for Huantai County farml and is 15.0gkg-1，which maybe the balance point under this specific farming system，soil types and climate conditions．There exists obvious positive relationships between SOM and crop yiel. The contribution of soil available nutrients (soil available nitrogen，SAN and soll available potassium，SAK)to grain production decreases with the increase of crop yield，and the contribution of soil available phosphorous(SAP)increases with the increase of crop yield．