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Penetration of Wax Layers by Cotton Roots as Affected by Some Soil Physical Conditions¹

ABSTRACT

The use of a wax layer for root penetration tests under controlled soil conditions has made it possible to separate from other factors in the soil the effect of mechanical impedance on the growth of plant roots. The penetration percentage of cotton roots increased as soil moisture tension was increased from 0.05 bar to 0.52 bar then decreased as tension was further increased to 10.8 bars. The penetration also decreased with increasing salt content in the soil solution. Decreased aeration as measured by CO₂ content also lowered the penetrating ability of cotton roots. An increase in bulk density of the soil from 1.0 g. per cc. to 1.4 g. per cc. did not affect the penetrating ability of cotton roots into the wax layer.

¹ Contribution from the Colorado Agr. Exp. Sta., Fort Collins, in cooperation with the Soil and Water Conservation Research Division, ARS, USDA. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree. Presented before Div. S-1, Soil Sci. Soc. Am., Denver, Colo., Nov. 18, 1963.

² Research Soil Scientist, USDA, and Associate Agronomist, Colorado Agr. Exp. Sta., Fort Collins, respectively.

Received for publication June 12, 1963. Accepted for publication February 20, 1964.