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Plow-Layer Porosity and Surface Roughness from Tillage as Affected by Initial Porosity and Soil Moisture at Tillage Time¹

ABSTRACT

Total porosity increase and random roughness due to plowing were each significantly affected by the moisture content at tillage time. Their magnitudes were greatest at low moisture contents, decreased approximately linearly as soil moisture increased to the lower plastic limit (LPL), and then increased at moisture contents greater than LPL. The porosity before plowing more significantly affected tillage-induced random roughness than total porosity increase. There were significant deviations from these generalities within each of the three soil associations: Barnes-Aastad, Kranzburg-Poinsett, and Nicollet-Webster.

In all three associations, the porosity decrease by subsqeuent disking and harrowing was more pronounced where plowing gave the greatest porosity increase. Only in the Kranzburg-Poinsett association (high in silt content) were porosity increases observed from disking and harrowing near and above the LPL. Disking and harrowing nearly always reduced random roughness, and the reduction increased linearly as the random roughness of the plow treatment increased.

Key Words: soil structure • antecedent porosity • antecedent moisture • soil consistency • infiltration

¹ Contribution of the Corn Belt Branch of the Soil and Water Cons. Res. Div., ARS, USDA, in cooperation with the South Dakota Agr. Exp. Sta. and the Minnesota Agr. Exp. Sta.

² Soil Scientists, Soil and Water Cons. Res. Div., ARS, USDA, headquartered at Morris, Minn.

Received for publication December 21, 1966. Accepted for publication March 7, 1967.