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A Field Study of Some Plant-Soil Relations in Aeration¹

ABSTRACT

An attempt has been made to bridge the gap between the knowledge of the oxygen requirements of roots which has been gained through laboratory studies and the empiricism which now exists in field studies of soil aeration. This objective has been sought through a theoretical approach which combines field measurements of the oxygen supply in the gaseous and liquid phases of the soil and known quantitative demands by plant roots for oxygen into a single expression derived from Fick's Law for radial diffusion. The concentration of oxygen at the root surface is the soil aeration parameter determined.

The application of the theory to the quantitative evaluation of soil aeration conditions in two contrasting soil types, Amarillo fine sandy loam and Miller clay, has led to the following conclusions:

1. At field capacity, the concentration of oxygen at certain root surfaces is suboptimal for normal root respiration in Miller clay, but optimum in Amarillo fine sandy loam.

2. The concentration of oxygen at the root surfaces increases linearly with the logarithm of soil moisture tension.

3. The apparent diffusion path length in the liquid phase about plant roots is more often a limiting factor in normal root respiration than the gaseous composition, per se, in the soil pores.

The above conclusions, based upon the application of the theory, were tested against plant response. The results obtained indicate that the method shows promise as a tool to estimate the supply of oxygen to roots under field conditions.

¹ Contribution from Western Branch, Soil and Water Conservation Research Division, A.R.S., U.S.D.A., in cooperation with the Department of Agronomy, Texas Agr. Exp. Sta., College Station, Texas. Presented before Div. I, Soil Science Society of America, Nov. 14, 1956, at Cincinnati, Ohio.

² Formerly Agents (Soil Scientist); now Graduate Assistant, Utah State University, Logan, Utah; and Soil Scientist (Physics), A.R.S., U.S.D.A., Ithaca, New York, respectively. Appreciation is expressed to Mr. Fred Keating and Mr. Grady Randel for their assistance with the Big Spring, Texas experiment.

Received for publication November 6, 1957. Accepted for publication January 17, 1958.