Oxygen Requirements of Cotton Seedling Roots for Penetration of Compacted Soil Cores

Cotton root growth and activity was determined at different levels of subsoil bulk density and O 2 concentration. Subsoil cores of desired bulk density were aerated leaving both the soil moisture content intact and the surface soil exposed to diffusion of gases from the atmosphere. Measurements of root growth and activity in the subsoils included depth of root penetration, root yield, water uptake, and carbon dioxide production in the subsoil. Mechanical impedance was more detrimental than low O 2 for root growth in the subsoils at bulk densities above 1.5 g. cm. ‐3 . At lower densities root growth was depressed at O 2 levels below 10%, and there was a strong interaction of O 2 and bulk density.