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The Absorption of Phosphorus from Phosphate Fertilizers Applied to Established Meadows: III. Effect of Phosphorus Source and Placement and of Meadow Composition¹

ABSTRACT

Three experiments were conducted to determine the absorption of phosphorus from concentrated superphosphate and calcium metaphosphate when applied to established meadows. They were located on Ida silt loam, a loess derived calcareous (pH 7.8) soil in western Iowa; Seymour silt loam, a loess derived acid (pH 5.8) soil in southern Iowa; and Floyd loam, a glaciated acid (pH 5.6) soil in northeastern Iowa. The differential phosphate treatments supplied 40 pounds of P₂O₅ per acre as concentrated superphosphate and <10 and <40 mesh calcium metaphosphate. Each phosphate source was applied broadcast or drilled in rows 7 inches apart and about an inch deep to compare placement.

It was found that either broadcasting or drilling the phosphate fertilizers studied was an effective means of supplying additional phosphorus to established meadows; however, the drilling operation appeared to decrease the forage yields slightly at all three locations. In addition, the plant absorption data for phosphorus showed that broadcasting was more effective than drilling as a method of applying calcium metaphosphate.

The finer <40 mesh calcium metaphosphate supplied a greater percentage of the plant phosphorus than did the <10 mesh material. The data indicate that superphosphate was more readily available to plants than was calcium metaphosphate, and that it might be preferred on extremely phosphorus-deficient soils. Otherwise it seems that calcium metaphosphate might be used on a phosphorus equivalent basis.

In general, the legumes derived a greater percentage of their phosphorus from the fertilizer than did the associated grass, especially in case of the first hay cutting and with calcium metaphosphate. These differences were not as consistent in the second cutting and in case of superphosphate.

¹ Journal paper No. J-2421 of the Iowa Agr. Exp. Sta., Ames, Iowa, Project 1189. This work was supported in part by a grant from the Tennessee Valley Authority, and in part by a grant from the Industry Committee on Radioactive and Tagged Element Research. The fertilizers were supplied by the Bureau of Plant Industry, Soils and Agricultural Engineering, U.S.D.A. The specially designed hoppers for drilling radioactive fertilizer were made under the supervision of G. A. Cumings, of the Division of Farm Machinery of the B.P.I.S.A.E. Through the cooperation of M. L. Jackson and the Agricultural Engineering Staff, the metal parts for adapting the hoppers to the drill were made in the Agricultural Engineering Shop of the University of Wisconsin.

² Associate Professor of Soils, Agronomy Department.