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Principles of Nutrient Uptake from Fertilizer Bands. VII. P³² Uptake by Brace Roots of Maize and Its Distribution Within the Leaves¹

The influence on phosphorus uptake of area of roots in the fertilized soil and the rate of fertilization was investigated using aerial brace roots of maize. Either 1 or 2 brace roots were directed into soil containing 0.62 or 3.10 g of phosphorus labeled with P³². The radioactivity of the tip and/or basal portions of all leaves was measured by wrapping one thickness of leaf around a long G–M tube. The distribution of P³² in several leaves was mapped with an end window G–M tube.

The P³² accumulation measured by the in-situ technique was highly correlated with that of the standard briquet method. Phosphorus uptake varied with the rate of fertilization and the number of fed brace roots. The proportion of total phosphorus derived from the fertilizer ranged from 1–37%.

The P³² distribution in the leaves depended upon their position relative to the fertilized brace roots. The leaves on the brace root side had higher P³² activity in their tip portions than in their basal portions. This distribution is explained by limited connections between vascular bundles of the stem and the diverging of the leaf veins from the midrib.

² Current addresses: J. A. Robertson, Department of Soil Science, University of Alberta, Edmonton, Canada; B. T. Kang, Faculty of Agriculture, University of Indonesion, Bogar, Indonesia; F. Ramirez-Paz, C.I.A.N.O., C. Obregon, Sonora, Mexico; C. H. E. Werkhoven, Agronomy Department, University of California, Davis, California; and A. J. Ohlrogge, Professor of Agronomy, Purdue University, Lafayette, Indiana. The authors are indebted to the following persons for contributions to this study: Wended Osborne, formerly an undergraduate student in Agronomy at Purdue University for the preliminary studies with methylene blue; and Ad van Egeraat, a special student from Holland on a 6-month program in the Department of Agronomy, Purdue University, for collection of much of the 1962 data and for contributions to their interpretation.

Received for publication October 27, 1965.