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Seasonal Fluctuations in Soil Structure and Erodibility of Soil by Wind¹

ABSTRACT

The objective of this investigation was to elucidate the effects of seasons on soil structure and erodibility by wind.

Little change in soil structure and erodibility occurred during a mild, dry winter near Lubbock, Tex., in 1952–53, but considerable change occurred during several consecutive winters in some areas of the Prairie soil zone of Kansas where the soils were usually moist.

Under moist conditions, frost action tended to break down the coarse water-stable aggregates and at the same time tended to consolidate the finest fractions to an intermediate size, especially between 0.05 and 0.42 mm. in diameter. The probable mechanism of frost action on soil structure is described.

Secondary aggregates and clods tended to break down during the winter to a size erodible by wind (<0.84 mm. in diameter). Soil erodibility was in most cases much higher in spring than in fall. The greatest increase in erodibility occurred in finest textured soils, the least in coarsest. Seasonal fluctuations in soil structure and erodibility seldom exceeded 3 inches in depth. Below this depth, the structure and erodibility changed little from season to season.

During the summer there was usually an increase in the coarsest and the finest water-stable soil fractions. It was concluded that the finest water-stable fraction (<0.02 mm.) contains materials essential for the building of primary and secondary soil aggregates.

¹ Contribution 493. Department of Agronomy, Kansas Agr. Exp. Sta., Manhattan, Kans., and the BPISAE, U. S. Dept. of Agriculture. Cooperative investigations in the mechanics of wind erosion.

² Professor of Soils, Kansas Agr. Exp. Sta., and Agent, Division of Soil Management — Irrigated and Dry Land Regions, BPISAE, U.S.D.A.

Received for publication September 25, 1953.