Subsoil Conditions and Their Effects on Oxygen Supply and the Growth of Corn Roots

Abstract The effects of subsoil density, fertility, and moisture content on soil aeration and root growth are reported. A factorial experiment having two levels each of subsoil compaction, fertility, and moisture was conducted. Oxygen diffusion rates in the subsoil were studied by two methods. Oxidation‐reduction potentials were determined. Corn roots did not penetrate a subsoil compacted to a bulk density of 1.5 g. per cc., but they grew profusely in subsoil with a bulk density of 1.2 g. per cc. Quantitative information was obtained on the rates of oxygen diffusion in the subsoil. Oxygen diffusion was slower in dense subsoils than in loose subsoils. High moisture content intensified the restricting effects of dense subsoils on oxygen diffusion rates and root growth. Subsoil fertilization increased corn root growth in loose soils. Plant growth was not correlated with oxidation‐reduction potentials within the limits found, but was correlated with gaseous diffusion through the subsoil. Oxygen diffusion rates which limit root growth are suggested.