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The oil present in the castor bean (Ricinus communis L.) has several applications, especially its use in the production of biodiesel. Therefore, the aim of this work is the response of low size castor bean to rates of phosphorus in conventional and narrow cultivation in second cropping season. The experimental design was a randomized complete block (2 x 5) design with four replications, being two population densities and five rates of phosphorus. The evaluated population densities were 67,340 and 33,670 plants ha-1(conventional), and the phosphorus rates evaluated were 0, 30, 60, 90 and 120 kg ha-1 of P2O5. The conventional cultivation resulted in higher stem diameter, plant height, number of racemo-1 grains, 100 grain mass, grain yield and oil yield. The number of racemes plant-1 was higher in the population density of 33,670 plants ha-1 when it was applied P. Phosphate fertilization contributed to increase grain yield (689 kg ha-1) and oil yield (311 kg ha-1), with a maximum technical efficiency rate of 80 kg ha-1 of P2O5. Castor bean sown in conventional cultivation with basic fertilization containing 80 kg ha-1 of P2O5 is a promising alternative for the second harvest.