The experiment was carried out in greenhouse from 17/ 8/1978 to 17/11/1978, on a Dark Red Latossol (LVe), medium texture. The potassic sources were: potassium chloride, a water soluble salt and four (4) samples of a insoluble potash mineral proceeding from the Plateau of Poços de Caldas, State of Minas Gerais, which were submitted previously to an hydrothermal treatment in order to alter its crystalline structure. Two levels of K(2)0 were applied, 100 kg K(2)0/ha and 200 kg K(2)0/ ha. The results showed no strong differences among the potassic materials regarding the quantity of potassium absorbed by the rice plant and the efficiency in the utilization of the potassium from those materials.