Sustainable potassium(K)management at different soil sites requires understanding the relationships between crop productivity and long-term K fertilizations on a regional or national scale. We analyzed responses of grain yield of wheat(Triticum aestivum L.)and maize(Zea mays L.), K efficiency, and partial balance(difference between K input through fertilizer and K output in the aboveground biomass)during 15-(1990-2005)or 18-year(1990-2008)K fertilizations at five distinctive agroecological zones across China. Compared to the inorganic nitrogen(N)and phosphorus(P)fertilization, the inorganic NPK fertilization significantly increased grain yields of wheat(21%)and maize(16%-72%)at Qiyang and Changping, where soils have low exchangeable and non-exchangeable N/K ratio in crop plants. Compared to the inorganic NPK fertilization, the inorganic NPK(30% N)and organic manure(70% N)fertilization(NPKM)increased grain yields of wheat(14%-40%)and maize(9%-61%)at four sites, but not at Zhengzhou. For a productivity of wheat at 2-5 t ha(-1)or maize at 3-6 t ha(-1), 13-26 or 9-17 kg K ha(-1)were required to produce 1.0 t wheat or maize. The NP fertilization resulted in the lowest negative partial K balance and accumulated 52 kg K ha(-1)year(-1)less than the NPK fertilization, which accumulated 28 kg ha(-1)year(-1)less K than the NPKM fertilization. A re-evaluation of the site-specific fertilization effects on N/K ratio in crop plants and soil K accumulation under current NPK and NPKM fertilization is urgently needed to increase both crop yield and K use efficiency at different agroecological zones across China.