Studies on the Basaltic Soils of Northern Ireland

Summary The cation‐exchange capacities of soil separates, isolated by the International soda method and decantation from five basaltic soil profiles were determined by the neutral normal ammonium‐acetate method of Schollenberger and Simon. The exchange capacities of the clays ranged from 41 to 60 m.e. per cent. The results suggest the presence of clays of the illitic type. Silt separates were found to have high cation‐exchange capacities, sometimes greater than those for corresponding clays. The fine sands also exhibited appreciable exchange capacities, the highest again being found usually in the lowest horizon of the profile. Values as high as 20 m.e. per 100 g. were obtained for some of the coarse sands. Part of the exchange capacity of the separates greater than 2 μ in effective diameter is undoubtedly due to the presence of some clay contaminant, but the actual silt and sand particles also comprise material with considerable exchange capacity.