Freezing cycle effects on water stability of soil aggregates

The freezing process is commonly implicated as a key factor in defining the state of soil structural stability following the winter months. Controversy exists, however, regarding the efficacy, and even the net effect, of this process. The objective of the study was to establish the separate effects of the freezing, freeze-thaw and freeze-drying processes in defining soil structural stability following the over-winter period. Aggregates from soils of varying clay content (0.11, 0.33, 0.44 kg kg(-1)) and initial water content (0.10, 0.20 or 0.30 kg kg(-1)) were subjected to freeze-only (F), freeze-thaw (FT) and freeze-dry (FD) treatments. Post-treatment aggregate stability determination was via wet aggregate stability (WAS) and dispersible clay (DC). Freezing alone and freeze-dry treatments generally resulted in greater aggregate stability, while the freeze-thaw generally resulted in lower aggregate stability as compared with a control, not frozen treatment (T). These data suggest the freezing-induced desiccation process improves aggregate stability, while the addition of a thaw component following freezing, with the attendant liquid water, is responsible for degradation of aggregate stability. Clay content and initial water content are important factors governing the magnitude of this process.