The potassium release characteristics and fixation abilities of five soils were studied by using depletion experiments and soil incubation experiments.The results were summarized as follows: With the extensive root systems ryegrass could draw up much of potassium from the soil potassium pool with in a short time.During the exhaustion cropping the soil deficient in potassium would quickly reach the lowest potassium value.In general,the lowest value of exchangeable potassium occurred at second harvesting and that of nonexchangeable potassium was obtained at third cutting,the lowest value changed with the tune of clay minerals.Potassium absorbed by plants mainly came from the soil interlayer potassium,among this,the potassium which could not be extracted by boiling with lmol/L HNO₃ was dominant.The more the soil K depleted,the more the applied potassium fized by soil.Under different water conditions,the amount of fixation of fertilized potassium was in the order of alternative dry and wet>constant wet>submerged.