Abstract A NUMBER of studies have been conducted to compare the utilization of phosphorus from soft phosphate and other phosphorus sources. The majority of these reports have indicated poor availability of the phosphorus from this source. These studies were reviewed by Motzok et al. (1956) and Nelson and Peeler (1961). Summers et al. (1959) attempted to improve the availability of phosphorus from soft phosphate by mixing it with phosphoric or hydrochloric acid. It was suggested that this process increased the availability of the phosphorus by an alteration of the chemical form. Nelson and Peeler (1961) reported that the biological value of combinations of phosphates was no better than the sum of the available phosphorus contributed by each source, with no synergistic effects observed. The purpose of the experiments reported herein was to determine the possible value of combining soft phosphate with combinations of phosphoric acid, sodium acid phosphate, and dicalcium phosphate…