Past research in Wisconsin and other mid-western states has shown that alfalfa will perform best when grown on well drained, near neutral soils that have adequate nutrition. In Wisconsin, potassium is of special concern because this nutrient is often needed for this crop. Potassium functions in several physiological processes in forage legumes. These include enzyme activity, carbohydrate production and transport, and stomatal activity (Munson, 1985). Wolf et al. (1976) found that K increased the carbon dioxide exchange rate of leaves. Peoples and Koch (1979) found that K deficiency slowed the rate of growth of both the shoots and roots and increased the rate of maturation to first flower. Potassium also balances the negative charges of organic and inorganic anions within the plant and appears to be involved in starch formation, translocation of sugars, nitrogen assimilation and several other metabolic processes. Potassium uptake is also linked to increased resistance to disease and lodging, increased carbohydrate production, and improved winter hardiness of alfalfa (Schulte and Walsh, 1993). The response of alfalfa to additional K may reflect the influence of this element on one or several of these factors.