Edwards, L. M. 2013. The effects of soil freeze-thaw on soil aggregate breakdown and concomitant sediment flow in Prince Edward Island: A review. Can. J. Soil Sci. 93: 459-472. The importance of aggregate size and integrity in soil productivity and crop production is paramount, and aggregate size reduction or increase invariably becomes a primary concern in such soil management practices as tillage and organic matter manipulation. In this regard, therefore, the present review looks particularly at the consequence of freeze-thaw cycling (FTC) on agricultural lands in Prince Edward Island (PEI) where an annual average of 40 cycles induce measurable aggregate breakdown with mixed consequences. On the one extreme, the consequences are manifest in increased soil erosion. On the other extreme, reduced (or reversed) soil compaction and improved seedbed conditions are welcomed consequences where temperature alternation breaks up hard pans or soil clods, or where the predominance of smaller aggregates can be an asset in seedbed environments, favouring improved crop emergence and early-spring establishment. In the PEI soils studied, the greatest changes in aggregate size distribution with FTC occurred in the largest and smallest size fractions wherein fractions <0.5 mm showed a 33% average increase while, simultaneously, the 4.75-9.5 mm fractions showed a 28% average decrease. This breakdown is reflected most contrastingly where FTCs to maximum (asymptotic) breakdown averaged up to 3.5 times for a loam as it did for a sandy loam or a fine sandy loam soil. This review also examines FTC in a broader agricultural and environmental context where it can potentially impact agro-sustainability. Where FTC effects on a fine sandy loam were measured in terms of erosion, there was a sediment mass increase of about 90% in interrill flow and about 25% in rill flow. Further, this review emphasizes methodology that has proven to be workable under the circumstances of PEI's dominant agricultural soils and the FTC research objectives that they helped to shape. It was considered important in this review, also, to highlight the need for expanded research (commencing with regional cooperation), particularly on frost depth, to feed into moisture-availability modelling towards improved clarity for end-user benefit.
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