Calcium (Ca), magnesium (Mg), and sulfur (S) are required for the growth and development of all higher plants. They are commonly referred to as secondary nutrients because they are less often limiting to plant growth than the primary nutrients nitrogen (N), phosphorus (P), and potassium (K), although secondary nutrients are as critical for crop growth and development as the primary nutrients. There is limited information available concerning secondary nutrient requirements of potatoes grown in southcentral Alaska. Laughlin (1966) conducted studies between 1961 and 1963 comparing potassium chloride (KCl) and potassium sulfate (K2SO4) as potassium sources for Green Mountain potatoes, and determined the effects of varying rates of magnesium sulfate (MgSO4) and K2SO4 on Kennebec potatoes. Since these studies were conducted without irrigation and at production levels about one-half those obtained by top producers in the Matanuska Valley today, it was considered appropriate to expand upon the previous work using current production practices. Potassium was supplied as KCl and K2 SO4 to explore the need for additional S under local potato production conditions and to determine the effects of the chloride (Cl) and sulfate (SO4) anions on production and quality of potato tubers. In addition, Mg and Ca were added to determine whether the background levels of these nutrients were adequate for optimum production.