The release characteristics of slowly available potassium in some cultivated soils was studied by 0 01 mol·L -1 oxalic
acid and H\|resin successive
extraction with Ca ++ saturated soil and pot exhaustion experiment The results showed the
releasing amount and rate of slowly available potassium in Soil 2,3 and 8 were much higher than those in others The averages of releasing amounts in Soil 2,3 and 8 by these two methods were 488 4 and 182 7 mg·kg -1 ,and those of rates were 66 8 and 15 0 mg·kg -1 ·h -1 respectively The average amounts of total and slowly available potassium absorbed by ryegrass in Soil 2,3 and 8 were 184 32 and 91 21 mg·kg -1 respectively So the availabilities of slowly available potassium in these soils were much higher than those in others The release capacity and rate of slowly available potassium in the soils by H\|resin extraction had close relation with the amounts of potassium absorbed and biomass of ryegrass.The H\|resin successive extraction with Ca ++ saturated soil could be the better method to evaluate availabilities of soil slowly available potassium There were remarkable correlation at 12h and most remarkable correlation at 96h extraction by H\|resin between releasing amount of slowly available potassium and total potassium absorbed by ryegrass,and the release amount of slowly available potassium at 96h were 83% of the total It is recommended that the extracting time by H\|resin successive extraction were 12-96 h