From a total of 216 trials with cotton fertilization carried out from 1957 through 1960, the results were put in correlation with the phosphorus contents of the soil. On account of the small number of favorable reactions to the nitrogenous and potassic fertilization, just that one only nutrient could be studied. Is was found out, however, that low levels of nitrogen and potassium (30 kilograms to the hectare) give a better consistence to the action of phosphorus. Considering 100 the best yield, it was possible to statistically establish the ratio between the contents of phosphorus of the soil and the percentages of yield. The correlation was highly significant, giving an explanation for the linear being about 50% and the quadratic one less than 10% for the soils of arenito Bauru. Thus, the equation was obtained leading to the higher percentage of yield by adding the phosphated fertilizer.