Strategic placement of P32 and root excavations revealed that roots of orchardgrass and bromegrass reached a greater depth when no N was applied. Nitrogen increased the root diameter and decreased the rate of elongation causing the plants to feed near the soil surface for a longer period of time. Defoliation stopped root growth within 24 hours and induced decomposition of the existing roots within 36 to 48 hours. Uptake of P32 placed in the existing root zone 24 to 48 hours after clipping was not detected until new roots reached the activated zone. New roots were initiated from basal leaf nodes of orchardgrass and rhizome nodes of bromegrass. Removal of all roots at the time of defoliation did not influence the rate of regrowth from transplanted sod plugs under optimum soil moisture conditions.

No 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.

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Subsoil fertilization experiments were conducted on several Indiana soils. The fertilizer was applied in vertical bands from 7 to 20 inches deep. The distance between the bands varied between 28 and 48 inches. The growth of corn roots greatly increased as a result of subsoil fertilization; subsoiling without fertilizing the subsoil increases root growth only slightly. Subsoil that was chiseled and fertilized maintained a higher porosity for over 2 years. The reason for the difference is probably the presence of additional organic matter (roots and microbes) in the fertilized subsoil. The subsoiled areas generally contained more moisture than the untreated plots, pointing to less runoff and erosion and to a greater water supply for the crops. Yield increases from subsoil fertilization have been substantial in many cases, but not consistent. It is assumed that benefits from this practice will increase as it is repeated on the same area.