Abstract: 【Objective】Effect of long-term potassium (K) fertilization on K fixation by soils under different cropping systems and climates was studied. 【Method】Samples taken from the NP and NPK treatments in three typical soils (viz., gray desert soil, fluvo-aquic soil and purple soil) were analysed for changes in K fixation and their affecting factors by the methods of simulating in laboratory and X-ray diffraction under long-term K fertilization. 【Result】When added K ranging from 0.4 to 4.0 g/L, the K fixation capacity and K fixation rate of purple soil in which hydromica content was low decreased significantly in NPK treatment, the decline value ranging from 91 to 559 mg/kg and 14% to 23％, while decreased slightly in fluvo-aquic soil in which hydromica content was abundant, the decline value ranging from 35 to 274 mg/kg and 6% to 8％, and remained unchanged in gray desert soil in which hydromica content was very abundant in the same treatment, compared with the NP treatment, respectively. The contents of SOC, CEC and <0.002 mm clay in tree soils remained unchanged under long-term K fertilization, while the slow available K content and K+ saturation increased ranging from 11.3 to 349.9 mg/kg and 11％ to 65％, respectively.【Conclusion】Long-term K fertilization arrested the transformation of hydromica into mixed-layered mica-smectite component and then K fixation capacity decreased. Besides, the increase of the slow available K content and K+ saturation induced the decrease of the K fixation capacity.

Key words: Long-term K fertilization, K fixation, Gray desert soil, Fluvo-aquic soil, Purple soil