The reduction in the electrical conductivity of a mixed solution of K2HPO4 and KH2PO4 caused by the addition of soil is a measure of the potassium uptake, and is therefore an indication of the “;base exchange capacity” of the soil at pH. 7. Two disturbing factors are noted, and it is concluded that the method is likely to be most useful where a rapid comparison of soils of a similar nature and pH is required.