Release rates of non-exchangeable potassium(NE-K) in 25 selected soils of 12 primary soil types from northern China were studied using a continuous flow apparatus and 0.10mol/L HCl as extracting solution.Results indicated that NE-K was released slowly for a long time.Maximum release rate of NE-K varied from 0.195 to 2.30mg/(kg·min),average release rate of NE-K in 600 minutes ranged from 0.066 to 1.121mg/(kg·min),and the NE-K release lasted for more than 600 minutes in most soils.The NE-K released in 600 minutes accounted for 5.4% to 39.6% of the total NE-K in the soils.Generally speaking,the release rate and percentage of soil NE-K gradually increased from the east to the west of China,the release parameter of NE-K were the highest in northwest soils and the lowest in the northeast soils,on average.The release rate of NE-K was very closely and positively correlated with the potassium uptake by corn seedlings in the potassium depletion experiment in greenhouse.Therefore,it could be used as a reliable index of potassium-supplying power in soil.