Oats, and in some cases mustard and buckwheat, were grown in a humus rich tchernoziem saturated respectively with H, NH4, Na, K, Mg, Ca, Sr, Cd, Ba, Mn, Fe++, Fe+++, Co, Ni, Cu, and Al; CaCO3 was added to one series and to all sufficient extra N, P, and K to insure their adequacy. Without CaCO3, plant growth equivalent to that in the original soil was obtained only in the Ca-saturated soil; almost as good growth was secured with the Sr-saturated soil. With CaCO3, the H-saturated soil produced normal yields; the Mg, Mn, Fe++, Fe+++, and Al soil gave some plant growth, whereas plants perished in the NIL, Na, K, Cd, Ba, Co, Ni, and Cu soils both in the presence and absence of CaCOs. Normal growth in the Ca saturated soil indicates that plants can get their needed K and Mg from non-exchangeable forms. Crop failure in some of the other soils is attributed in part to the plant''s inability to secure its needed Ca from non-exchangeable form. The important role of soil Ca for normal plant development is emphasized.