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Effect of Soil Overburden Pressure on Penetration of Fine Metal Probes¹

ABSTRACT

The interactive effect of overburden pressure and root confinement on root elongation in a fine-structured loam soil has been examined using fine-metal probes to simulate a plant root. Substantial increases in probe resistance with simulated overburden pressure were found only at high soil bulk densities and high ratios of probe to soil volumes. These findings suggest that for low root to soil volumes (root density) and the maximum soil density used, 1.63 g cm^-3, the elongation rate of plant roots at a depth of 150 cm would be only 4% less than in the surface layer. For root densities in excess of 0.01 and the same bulk density and depth of overburden, the model predicts a 30% reduction in elongation rate.

¹ Contribution from the Corn Belt Branch, SWCRD, ARS, USDA, St. Paul, Minn., in cooperation with the Iowa Agr. & Home Ec. Exp. Sta., Ames, Iowa. Appreciation is expressed to the Iowa State Highway Comm. for financial support. Journal Paper J-6303 of the Iowa Agr. & Home Ec. Exp. Sta.

² Research Associate and Soil Physicist, Iowa State Univ., Ames, Iowa, and Soil Scientist, USDA, St. Paul, Minn.

Received for publication May 27, 1970. Accepted for publication October 9, 1970.