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The Importance of Subsoil Phosphorus to Corn¹

ABSTRACT

In order to determine the depth to which the corn plant feeds, field studies were conducted to measure the recovery of P³² from successive 6-inch soil horizons. The available soil phosphorus in these horizons was determined by the Truog, Olsen, and Bray No. 2 tests. The accuracy of these tests was checked by correlations with A values and phosphorus uptake data obtained from greenhouse studies.

Corn recovered more fertilizer phosphorus from the 6- to 12-inch horizon of 2 of the 4 soils studied than from the plow layer and in the other soils recovery was almost as great as from the plow layer. Recovery from any layer below the 12-inch depth was considerably less than from the top 2 layers, but the combined recovery from these lower layers was appreciable. This indicates that a large percentage of the phosphorus in the corn plant may come from the subsoil if the subsoil is fairly well supplied with available phosphorus. In most cases, the available phosphorus in the plow layer of the soils studied was greater than that in any of the respective subsoil horizons. However, it was much less than the combined amount found in all of the subsoil penetrated by corn roots.

According to the greenhouse studies the three phosphorus tests used gave an accurate measure of the available phosphorus in the subsoils as well as that in the plow layer.

Contribution from the Department of Soils, University of Wisconsin, Published with permission of the Director, Wis. Agr. Exp. Sta., Madison, Wis. This paper represents portions of a thesis submitted by the senior author to the Graduate School of the Univ. of Wis. in partial fulfillment of the requirements for the Ph.D. degree. The investigation was supported in part by fellowship grants from Swift and Company and the Musbach Fund. Presented before Div. IV, Soil Science Society of America, Nov. 15, 1956 at Cincinnati, Ohio.

² Assistant Professor and Associate Professor of Soils, respectively.

Received for publication December 14, 1956. Accepted for publication September 6, 1957.