7Dawe D,Steve F,Li C S.Trends in rice-wheat area inChina[J].Field Crops Research,2004,87:89-95.
8Yadav R L,Dwivedi B S,Prandey P S.Rice-wheatcropping systems:assessment of sustainability undergreen manuring and chemical fertilizer inputs[J].FieldCrops Research,2000,65:15-30.
9Kirk G J D,George T,Courtois B,et al.Opportunities to improve phosphorus efficiency and soilfertility in rained lowland and upland rice ecosystem[J].Field Crops Research,1998,56:73-92.
10Willett I R.Causes and prediction of changes inextractable P during flooding[J].Australian Journal ofSoil Research,1989,27:45-54.