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Sources of Phosphorus for Plants Grown in Soils with Differing Phosphorus Fixation Tendencies¹

ABSTRACT

Several phosphates of varying water solubilities were evaluated as sources of P for plants grown in soils with different degrees of P fixation. With relatively low fixation, P content of corn (Zea mays) seedlings increased in direct proportion to water solubility of "available" P. With high fixation, P content decreased with increased water solubility of P. Under the latter conditions, liming the soil or banding the P decreased P fixation; but the amounts were small relative to total P fixed. On slightly acid soils (pH 5.6 to 6.5) where response was obtained to applied P by six crops (corn, alfalfa, German millet, buck-wheat, wheat, or rice under both field and growth chamber conditions) 20% acidulated material was superior to 100% acidulated material in 16 cases, equal to 100% acidulated material in 55 cases, and inferior to 100% acidulated in only 17 cases. Where yields from the two materials differed significantly, differences were also observed in the effect of added P on soil available P (Bray P-1). Since the efficiency of solubilization of P in rock phosphate by H₃PO₄ decreases with rate of acidulation, and the unreacted rock phosphate evidently enhances plant recovery of soluble P, partially (20%) acidulated rock phosphate is a reasonable choice for soils of high P fixing tendency.

¹ Published with the permission of the Director of the Ohio Agricultural Research and Development Center as Journal Article 12–70. Presented before Div. S-4, Soil Science Society of America. Detroit, Mich. Nov. 12, 1969. Financial support for an assistantship for the junior author from the International Minerals and Chemical Corp. is gratefully acknowledged. Data in this paper come in part from M.S. Theses by L. G. Agustin. and the junior author, The Ohio State University, 1964 and 1969, respectively.

² Professor and Research Associate, The Ohio State University and the Ohio Agricultural Research and Development Center.

Received for publication June 15, 1970. Accepted for publication September 2, 1970.