Effect of Freeze-Thaw on Water Stability of Aggregates in a Black Soil of Northeast China

Soil aggregate stability, an important index of the physical characteristics of a soil, can provide a good indication of a soil's erodibility, and deserves special consideration in regions with cold climate. The objective of this study was to study the effect of freeze-thaw on soil water-stable aggregates in the black soil region of Northeast China. Samples of a typical black soil in the region were collected to measure water-stable aggregates after freeze-thaw under different conditions (i.e., initial moisture contents, freezethaw cycles and freezing temperatures) by wet-sieving into eight particle size groups (> 10, 10-6, 6-5, 5-3, 3-2, 2-1, 1-0.5, and 0.5-0.25 mm). Freeze-thaw had the most effect on aggregate stability when the samples had an initial moisture content of 400 g kg(-1). The water-stable aggregates of the four larger particle size groups (> 5, 5-3, 3-2, and 2-1 mm) reached a peak stability value, but those of the two smaller particle size groups (1-0.5 and 0.5-0.25 mm) reached a minimum value when the soil moisture content was 400 g kg(-1). Water-stable aggregates of the four larger particle size groups decreased while those of the two smaller particle size groups increased with the increase of freeze-thaw cycles. As temperatures fell, the water-stable aggregates of the four larger particle size groups decreased while those of the two smaller particle size groups increased.