THE EFFECT OF FREEZING-THAWING AND WETTING-DRYING CYCLES ON SOIL AGGREGATION

Abstract

Three fractions: 1) natural aggregates 2 to 3 mm.; 2) aggregates < 0.25 mm. prepared by crushing 2- to 3-mm. aggregates; and 3) aggregates < 0.25 mm. obtained by sieving the dry soil, were acquired from the Waupoos silty clay loam. After five cycles of wetting and drying, and freezing and thawing, the mean weight-diameter (M.W.D.) was determined after wet-sieving. Cycles of wetting and drying increased the M.W.D. of the large aggregates but did not cause significant changes in the fractions < 0.25 mm.Cycles of freezing and thawing at moisture contents near saturation significantly decreased the M.W.D. of the large aggregates and increased the M.W.D. of the crushed aggregates at both rates of freezing. A significant decrease occurred in the M.W.D. of the original aggregates < 0.25 mm. at the slower rate of freezing.