The residual effect on cotton development and yield of one application of plain superphosphate was compared to that of fused phosphates foscal, foscadu and fosleucal on Ortho-Red-Yellow Podzolic soil of the State of São Paulo (Brazil), during three years. Plain superphosphate had great influence upon cotton yield and plant precocity in the first year of residual effect. The effect upon cotton yield was directly proportional to the dose applied and decreased gradually after the second year of residual effect. Such effects of fused phosphates was smaller than that of plain superphosphate. In the third year after fertilization, the relative effects of foscal and of foscadu showed a sligth tendency to increase. But the general effects of fused phosphates indicate the impossibility of a favorable competition with plain superphosphate in furnishing phosphorus to cotton.