In this third paper on phosphorus fertilizers for corn the authors report the results obtained in three trials conducted in lhe State of São Paulo, one of which was carried out in 1945-46 at Ribeirão Prêto, other between 1947-48 and 1949-50 at Engenheiro Hermilo and the third from 1947-48 up to 1950-51 at Ipanema. In the Ribeirão Prêto trial, which was located in the plots used during some years for an identical experiment with cotton, there was no response to phosphorus and the phosphates studied - superphosphate, Serranaphosphate, Cibraphosphate and bone meal - gave similar results. In the experiments of Ipanema and Engenheiro Hermilo, where the response to phosphorus was very high. Serranaphosphate, bone meal and Algerian phosphate (ground rock phosphate) were much inferior to superphosphate. While the Ribeirão Prêto trial was carried out on «terra-roxa-legitima» soil, the others were located on sandy soils of the «glacial» type. Is seems, however, that the relative efficiency of the phosphates studied did not depend essentially on the soil type, but above all on the degree of phosphorus deficiency in the area used for each experiment.