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Soil Crusting and Some Factors Affecting It¹

ABSTRACT

Physical studies were made of natural soil crusts and of the soils beneath them. Artificial crusts (briquets) were prepared by several methods and their modulus of rupture and bulk density were determined. The natural crusts had a much greater bulk density, a higher percentage of particles < 0.10 mm. in diameter, and a lower degree of aggregation than the underlying soil. The modulus of rupture of artificial crusts was increased by longer periods of drying at 105°C.; by slow drying (using lower temperatures); by compacting the dry soil in the briquet molds; by the beating effect of raindrops; and by puddling the soil before putting it into the molds. It was decreased by successive wetting and drying, but partial drying and rewetting gave results which varied with different soils. High modulus of rupture values were obtained with soils containing large amounts of soilt or total material < 0.10 mm. and, 2:1 type clay. Bulk densities were essentially the same: (a) for dry soil used in preparing briquets and the same type of soil beneath natural crusts in the field; and (b) for artificially prepared briquets and natural soil crusts.

¹ Contribution from the Department of Soils, North Carolina Agr. Exp. Sta., Raleigh, North Carolina. Submitted with the approval of the Director as paper No. 759 of the Journal Series.

Part of a thesis submitted by the senior author to the graduate school of North Carolina State College in partial fulfillment of the requirements for the degree of Master of Science in soils.

² Rockefeller Foundation Fellow, North Carolina State College, 1955–56, Soil Scientist of the Instituto de Ecologia e Experimentacao Agricolas and Assistant Professor of the Universidade Rural, Rio de Janeiro, Brazil; and, Professor of Soils, North Carolina State College, respectively.

Received for publication September 21, 1956. Accepted for publication May 6, 1957.