Abstract:Pot experiment was adopted to study the effects of nitrogen supplying levels and rice cultivars on five forms of soil K in three purple paddy soils in Sichuan basin. Results indicated that the total K in the tested purple paddy soils was low to medium ranged from 1.29% to 2.62%, and mineral K accounted for 96.82% while quickly availble K and slowly available K only accounted for 0.62% and 2.56%, respectively on average. The potassium supplying power of the tested soils showed the following order neutral purple paddy soil>calcareous purple paddy soil>acid purple paddy soil. Nitrogen application(0～150mg/kg) increased the release of soil potassium and the utilization of non exchangeable K and mineral K. In accordance with the total amount of net K uptake by rice, the contribution of non exchangeable K and mineral K accounted for 80.3%. The capability of potassium uptake by four rice cultivars was Kaiyou 5>Shanyou 63>Eryou 6078>Ying jia 1 in neutral purple soil. Contibution of non exchangeable K and mineral K to K uptake by four rice cultivars accouted for 66.9% after the application of nitrogen fertilizer on average. The maximun of net K uptake by four rice cultivars were obtained at medium nitrogen level (N 150mg/kg). It was not beneficial to the K uptake by rice and the release of soil mineral K at low or high nitrogen level.