In this paper, the correlation between cotton responses to fertilization, and percentage of base saturation in soils, in the State of São Paulo, is discussed. A second degree polynomial, based on data collected from 126 experiments, was found to fit the data satisfactorily, with a correlation coefficient R = 0.676xx. The results indicate the possibility of estimating the effects due to fertilization in cotton crops, by use of the mentioned chemical characteristic of soils.