Fertilizer Evaluation of Certain Phosphorus, Phosphorous, and Phosphoric Materials by Means of Pot Cultures¹

Pot cultures of red clover, ryegrass, alfalfa, brown-top millet, and soybeans on representative soils were utilized in the fertilizer evaluation of distinctive phosphorus carriers--orthophosphoric acid, superphosphoric acid, metaphosphoric acid, phosphorous acid, superphosphite, calcium phosphite, phosphorus nitride, white phosphorus, red phosphorus, concentrated superphosphates from H3PO4 that carried different proportions of H3PO3, and mixtures of separately prepared superphosphate and superphosphite. Phosphoric acid, superphosphoric acid, metaphosphoric acid, and concentrated superphosphate registered high effectiveness. Phosphorus nitride (P3N5) and red phosphorus induced no plant response. White phosphorus proved injurious to the seedlings and virtually inhibited plant growth. Phosphorous acid and calcium phosphite were decidedly toxic to the initial crops but were beneficial to the succeeding crops. Although initial crops registered better responses to superphosphate than to any phosphorous material, the superphosphite residues induced excellent responses by the succeeding crops. Increases in plant response resulted from increase in ratio of phosphate to phosphite in the incorporated mixtures of superphosphate and superphosphite. The larger second-crop responses to the phosphorous materials were interpreted as reflecting the transformation of phosphite to phosphate in the soil. For a given input of phosphorus, every response to a phosphorous material was greater on the limestoned soils than on those not limed. Concentrated superphosphate is not diminished in effectiveness when it is produced through acidulation by means of H3PO4 that contains relatively small proportions of H3PO3. Concentrated phosphorous materials are not suitable fertilizers.