Studies were conducted to evaluate the interactions of P, K, and S applied to alfalfa grown on a calcareous silt loam. Phosphorus fertilization increased alfalfa yields. The application of K and S had no significant influence. In each of 2 years, the highest yields were obtained at the highest rate of P used. There was residual response to P applied in the previous cropping year. The P content of the alfalfa tissue was increased by P fertilization. The use of K and S had no influence on the tissue content of the respective nutrient. Soil P as measured by the bicarbonate extractant was related to previous P fertilization. This was not true for soil P extracted by the Bray procedure. The data in this study support the choice of the bicarbonate method for describing the P levels in calcareous soils.