Abstract: The long term effects of various combinations of nitrogen（N）, phosphate（P）, and potassium (K) application, NPK integrated with crop straw or organic manure on potassium balances and potassium pools were studied under continuous winter wheat-summer maize cropping system in a manural loess soil in Shaanxi of China. The long term experiment included nine applications of the recommended doses, unamended control (CK), nitrogen (N), nitrogen and potassium (NK), phosphorus and potassium (PK), nitrogen and phosphorus (NP), nitrogen phosphorus and potassium (NPK), wheat/maize straw (S) with NPK (SNPK) and dairy manure (M) with NPK (M1NPK and M2NPK). The results show that except for the NK, PK and M2NPK treatments, the total K removals by crops exceed the quantities of total K applied to the soils in other treatments, where the net negative K balances were observed ranging from 617 kg/ha in the plot of M1NPK to 4333 kg/ha in NP treated soils over 20 years. Compared with soil total K content of the initial soil at the start of experiment, the long term fertilization and cultivation have no significant effects on soil total K. Nevertheless, soil available potassium contents are significantly increased by the long term addition of potassium(containing fertilizers or manure), but it remains unchanged on the treatments without K addition. The contents of nonexchangeable K extracted in 9 sequential extractions with boiling 1 mol/L HNO3 (Mactotal K), particularly Step K, which is considered to be the most soluble fraction of Mactotal K, are substantially lower than their initial values, which suggests that Step K could be used as an indicator of K depletion for the investigated soil. Considering the cost of K fertilizer and the efficient use of existing K resources (such as straw, manure), incorporation of crop straw/stalk or organic manure into soil is, therefore, necessary in the long run under continuous winter wheatsummer maize cropping system in the manural loess soil in order to maintain soil K fertility and sustain land productivity.