The effect of alternate freezing and thawing on aggregate stability and aggregate size distribution of some Prince Edward Island soils

The effect of 1–15 daily freeze/thaw cycles on aggregate stability (S) and aggregate-size distribution measured as mean-weight diameter (MWD) was investigated for loam, sandy loam and fine sandy loam (FSL) soils; and two aggregate-wetting procedures, spray-wetting and vacuum-wetting, were compared. Initially, S and MWD decreased rapidly until about the fifth freeze/thaw cycle, thereafter change occurred progressively less rapidly reaching a minimum value at about the 10th cycle. Sand MWD in the loam, which had the greatest content of clay and iron oxides, decreased significantly less rapidly than in the other soils. The sandy loam, with the least clay but the most organic matter, was intermediate in behaviour. Macro-aggregate (>4.75 mm) content of the FSL decreased from 40% initially to 12% of total mass by the 15th cycle, while the micro-aggregate (<0.5 mm) content increased from 19% to almost 70% of total mass. In contrast, the loam retained many macro-aggregates, with a decrease from an 80% macro-aggregate content to 60% of total mass by the 15th cycle. With an average of about 40 freeze/thaw cycles occurring during a Prince Edward Island winter, S and MWD in both the sandy loam and the FSL will reach minima by the end of winter. In contrast, Sand MWD in the loam will not have reached a minimum by the end of winter. These results are related to the erosive behaviour of the three soils. Data on S and MWD of samples exposed to the two wetting procedures followed similar trends with number of freeze/thaw cycles (r=0.84 to 0.99); but spray-wetting gave less variable results than did vacuum-wetting and was a simpler procedure.