To study variations of soil potassium-bearing minerals,Q/I relation and soil capacity of fixing extraneous K,data from 18 long-term stationary field experiments with K treatments and zero K treatment were cited.The results show that (1) readily available K and slowly available K were higher in Treatment NPK than Treatment NP,with the latter being on average 7.67 mg kg^-1 a^-1 higher in hydromica-or smectit-edominated soils.(2) Due to long-term zero K application,crops depleted soil K,thus making hydromica weather and turn into vermiculite.Application of adequate K could defer or stop the process.(3) As a result of long-term zero K application,soil-△K° band AR_e^k were declining while PBC^k ascending,which means that the pool of readily releasable K in soil was getting smaller,K adsorption capacity of the soil higher,and soil K supply capacity lower.A higher rate of K should be applied if K concentration in the soil solution was to be increased.(4) As a result of long-term zero K application,soil K was depleted,which led to strengthened soil K fixation capacity for extraneous K.However,once NH₄⁺-N was accumulated in soil to a certain level,soil K fixation capacity for extraneous K would be reduced.