The cultivation of rice is the main agricultural activity of Roraima, which makes intensive use of phosphorus and potassium, so much in areas with several years of cultivation as in areas in the first year of agricultural activity. The aim of this study was to evaluate the response of irrigated rice to the application of different doses of phosphorus and potassium above the grains productivity, determined by the crop of the usuful area of the portion(3 x 2,5), em kg ha-1, height of plants in cm, measured in ten randomized plants for portion and production components.The Data were obtained by collecting ten panicles per plot in the useful area, being the thousand grain mass obtained from the weighing of grain in a precision scale and corrected to 13% number of filled grains, grain number and total number of sterile grains per panicle, and made his total score divided by the number of panicles, in areas of first year and heavily fertilized areas. It was used a completely randomized design in a split plot, being done through regression analysis of response surface. In the new area, the potassium affected significantly and positively all variables, except thousand grain mass, being its effect the primarily responsible for the productivity achieved. The phosphorus positively influenced the weight of thousand grains and productivity. The number of grains per panicle, weight of thousand grains and height contributed to the higher yields. The highest productivity (8,154 kg ha-1 grains) occurred with the use of 304 kg ha-1 of P2O5 and 228 kg ha-1 of K2O. The maximum economical efficiency was with 134 and 158 kg ha-1 of P2O5 and K2O, respectivelly, and productivity of 7501 kg ha-1, of net profit of R $ 696.78 ha-1 benefit / cost and unit cost of 1.18 U.S.$ 0.5271 kg-1 of rice. In the area of intensive cultivation the potassium affect the number of seeds sterile, the plant height, and panicles per m². The phosphorus changed the mass of thousand grains, number of sterile grains and total grains per panicle. There was an interaction for mass of thousand grains. Only the potassium influenced on productivity at 6522 kg ha-1. The order of accumulation of nutrients was N> K> Ca> P> Mg. The potassium influenced the variables, except available phosphorus in soil. Phosphorus only change their content in soil. The high levels of these nutrients in the soil not possible positive response to fertilization with phosphorus and potassium. The potassium caused decrease in the absorption of magnesium due to its low content in the soil, with reduced productivity by nutritional imbalance.
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