The Influence of Frost Action on Soil-Aggregate Stability

Change in aggregation as a result of frost action was measured for 154 samples from Alberta, Canada. Samples were subjected to one cycle of freezing at --I?C, -25?C and -46?C and to ten cycles at - i?C. Each pattern was tested twice, on air-dry and on saturated samples. Little change occurred in air-dry samples, but many saturated samples showed acute change. Freezing once at --I?C produced increase in aggregation, but all other patterns produced marked decreases. These changes are discussed in relation to soil characteristics, and a general theory, in which the location of freezing nuclei and the moisture content are of prime importance, is advanced to explain the observations. MANY soil properties are significant in geomorphological processes, but the stability of soil aggregates appears to be of most fundamental importance. Together with other parameters of soil aggregation it controls both percolation capacity and particle detachability, and therefore the erodibility of soils (R. B. Bryan, I969a). Experimental work has demonstrated that the most efficient indices of soil erodibility are those based on measures of aggregate stability, although actual soil losses may depend on many other factors (Bryan, 1968a). Soil