[Effects of freeze-thaw cycles on aggregate stability of black soil]

The stability of 3-5 mm aggregates of black soil collected from Heilongjiang Province were analyzed by Le Bissonnais method under different freeze-thaw cycle treatments (0, 1, 3, 5 and 9). The aggregate porosity were measured by wax-coated method. The results showed that the contents of different size aggregates fluctuated with the freeze-thaw cycles, and the variation coefficient of aggregate content turned stable gradually. There were significant differences of the content of above 0.25 mm aggregate among the treatments of fast wetting, slow wetting, and wet stirring. Aggregate porosity increased with increasing freeze-thaw cycles, ranging from 32.4% to 41.4%. Low variation of aggregate contents occurred in different breakdown patterns with increasing freeze-thaw cycles. There was negative correlation between porosity and mean weight diameter, suggesting the aggregate porosity was important in the aggregate stability under freeze-thaw condition.