Abstract: Taking the cropland soil in typical phaeozem region of Northeast China as test object, this paper analyzed its dry-sieved and water-stable aggregates composition, disruption rate (PAD_0.25, PAD_1.0), mean mass diameter (D_mm), mean mass soil surface area (SA_mm), and fractal dimension (D) under different water supplement and different frequency and rate of freeze-thaw cycle, aimed to study the effects of seasonal freeze-thaw cycle on the top soil aggregate characters in the region. No water supplement plus no freeze-thaw cycle and no water supplement plus freeze-thaw cycle increased the amounts of >5 mm dry-sieved and >0.25  mm water-stable aggregates significantly, and the D_mm of the aggregates by 7.98%-29.41% and 36.11%-44.44%, respectively. The measurement of SA_mm and D also indicated the promotion of the aggregation of macroaggregates. However, smaller water supplement plus freeze-thaw cycle and seasonal freeze-thaw cycle increased the amounts of <2 mm dry-sieved aggregates and 0.25-1 mm water-stable aggregates significantly, accelerated the disruption of air-dried aggregates, and decreased the SA_mm and D of water-stable aggregates by 10.88%-25.52% and 1.02%-3.40%, respectively, indicating that aggregation was somewhat promoted. After seasonal freeze-thaw cycle, the PAD_0.25 decreased by 33.45% (P<0.05) but PAD_1.0 had less change, suggesting that the seasonal freeze-thaw cycle in typical phaeozem region did not weaken soil splash-resistibility, while strengthened the water-stability of soil aggregates.

Key words: phaeozem, seasonal freeze-thaw cycle, soil aggregate, mean mass soil surface area, salt and alkali, grapevine, ion distribution.