Effects of Phosphate Fertilization and Dietary Mineral Supplements on the Nutritive Value of Soybean Forage1

1.Data from two crops (1948 and 1950) showed that phosphate fertilization doubled the yield of soybean forage and produced a plant (+ P) having a higher concentration of calcium and phosphorus but a lower leaf percentage, by weight, than the plants grown on soil not fertilized with phosphate (- P).2.A rabbit assay is described which was successfully employed in the study of the relative nutritive value of these crops. Rabbits fed diets containing the - P forage made smaller gains and had a lower level of inorganic phosphorus in the blood serum, and bones of greater fragility, than did those fed the diets containing the +P forage.3.A supplement of CaHPO4(M) added to the test diets not only eliminated the differences observed between the non-supplemented diets, but in addition the rabbits on the - PM forage diet gained more than those on the + PM forage diet. Data on the digestible nutrients of these diets and spectrographic analysis for 8 other elements offered no explanation for the last-observed difference.4.Phosphorus concentration and a factor not identified, but possibly associated with leafiness, were the principal differences found between soybean forages differentially fertilized with phosphate.