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A Field Measurement of Total Porosity and Surface Microrelief of Soils¹

ABSTRACT

Total porosity of the layer to be plowed was estimated from undisturbed cores collected before primary tillage. Using a point quadrant instrument, soil surface elevation measurements were made before and after preplant tillage, and after each cultivation to determine the effects of tillage on total porosity of the plowed layer. Large apparent differences in capacity to detain water, as inferred from total porosity, were observed among preplant tillages and among particular combinations of preplant and postplant tillage that are used in the western Corn Belt.

When total porosity of the plowed layer was measured in the ensuing fall and spring, relatively small changes in total prosity were observed. This result suggests that this physical property persists over a long time in a Barnes loam.

To evaluate the effects of tillage on surface geometry and temporary water storage in surface depressions, macro and random surface roughness as measured by the point quadrant instrument are considered. Estimates of the standard error among logarithm of the elevation heights differed among tillage treatments. The standard error is suggested as an index of random roughness.

¹ Contribution from the Soil and Water Conservation Research Division, ARS, USDA, in cooperation with the Iowa Agr. and Home Econ. Exp. Sta. and the Minnesota Agr. Exp. Sta. Journal Paper No. J. 4485 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project No. 1486. Presented before Div. VI, Soil Science Society of America, Ithaca, N. Y., August 1962.

² Soil Scientists, Soil and Water Conservation Research Division, ARS, USDA, headquartered at Morris, Minn., and Ames, Iowa.

³ The authors express their appreciation to Leon Sloneker, Agricultural Research Technician, for assistance with field plot experiments, and Elton A. Hallauer, Digital Computer Programmer, for computational assistance.

Received for publication January 23, 1963. Accepted for publication April 24, 1963.