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Effect of Freeze-Thaw Cycles on Aggregate Stability and Hydraulic Conductivity of Three Soil Aggregate Sizes¹

ABSTRACT

The study reported here was conducted to determine freeze-thaw influences on the vertical hydraulic conductivity of soil. To accomplish this three soil aggregate sizes (0.0 to 0.8 mm, 0.8 to 1.2 mm, and 1.2 to 2.0 mm) were packed in aluminum cores, equilibrated at two water levels (maximum water-holding capacity and 0.5 bar of pressure) and subjected to 20 freeze-thaw cycles at two freezing temperatures (–4C and –18C). Hydraulic conductivity and aggregate stability were determined for all cores before and after the freeze-thaw cycles.

Generally, water-stable aggregate breakdown was statistically greater at maximum water holding content. The percentage of water-stable aggregates in the 0.0- to 0.8 mm aggregate class increased by a factor of 1.26 from initial values after freezing and thawing at the 0.5 bar water level and –4C freezing temperatures.

Freezing and thawing caused the greatest decrease in vertical hydraulic conductivity of those cores with large aggregates and high water content subjected to the –18C freezing temperature. Freezing and thawing of cores at 0.5-bar water content generally increased hydraulic conductivity. An exponential relationship seems to exist between the change in the ratio of final to initial hydraulic conductivity and the soil water content at freezing. Drainage of soil water from surface horizons could induce freeze-thaw improvement of the soil's vertical hydraulic conductivity.

¹ Contribution from the New England Watershed Research Center, Northeast Area, Soil, Water and Air Sciences, ARS, USDA, and the Vermont Agr. Exp. Sta. Journal Series Paper No. 291.

² Soil Scientist, SW&A, Agr. Res. Service, USDA, NEWRC, 150 Kennedy Drive, So. Burlington, Vermont 05401.

Received for publication June 23, 1972. Accepted for publication September 6, 1972.