In this paper the authors report the results of an experiment in which the residual effect of potash, observed in the corn crop, was very high. Adding the reported results to those obtained in published experiments which were reviewed, they concluded that in some soils of the State of São Paulo the residues of potash applications are retained in such quantities and forms that may influence favorably the succeeding crops. They suggest, finally, investigations on the possibility of reducing the rate of application of potash in soils fertilized with it in the previous crops.