The authors report the results of four fertilizer experiments with cotton on "massapê-salmourão" soil, at the Mococa Agr. Exp. Sta., São Paulo. While one of them proceeded in the same plots from 1940-41 to 1943-44, the other three were annual and located near the former, but in areas differently fertilized in the previous crops. The annual trials were conducted in 1940-41, 1941-42 and 1942-43. The results showed high residual effect of the phosphorus fertilizer and, consequently, the possibility of reducing the quantity of that nutrient to be applied on soils fertilized with it in the previous crops.