Effect of nitrogen application and rice cultivars on forms of potassium in different purple paddy soils

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 soilcalcareous purple paddy soilacid 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 5Shanyou 63Eryou 6078Ying 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.