Effects of freeze-thaw cycles on aggregate stability of sandy loam on the Eastern Qinghai-Tibet Plateau

Freeze-thaw cycles (FTCs) have an important effect on soil aggregate stability by altering soil structures, thereby influencing soil wind and water erosion on the eastern Qinghai-Tibet Plateau. However, the effects of FTCs on the stability of these soils remain unclear. Here, we conducted freeze-thaw simulations in laboratory to investigate the effects of FTCs (0 to 15 cycles) on the wet- and dry-sieving aggregate stability of undisturbed sandy loam from Maqu county, which was treated with different initial soil moisture contents (1% to 25% in increments of 4%) and initial aggregate diameters (< 2, 2–5, 5–10, and 10–15 mm). Results show that soil aggregates with initial diameters larger than 2 mm exhibit higher soil organic carbon contents (1.45%–1.57%) and silt contents (34.63%–35.52%) than those smaller than 2 mm (0.93% and 31.38%, respectively). The stability of both wet- and dry-sieving aggregates increases with larger initial diameters. Increasing initial soil moisture content from 1% to 25% reduces aggregate stability, with reductions of 2.4%–88.0% for wet-sieving aggregates and 2.1%–25.5% for dry-sieving aggregates (> 2 mm). With increasing FTCs, wet-sieving aggregate (> 2 mm) stability exhibits a fluctuating upward trend, with increases of 79.2%–87.4% after 15 FTCs, while dry-sieving aggregate (> 2 mm) stability decreases significantly (5.7%–21.7%) upon the first FTC and remains unchanged thereafter. The stability of both the wet- and dry-sieving aggregates smaller than 2 mm remains unchanged with increasing FTCs (p > 0.05). SOC content decreases by 22.3% on average with increasing FTCs from 1 to 15 and shows no significant correlations with wet- and dry-sieving aggregate stability. Higher silt content (r = 0.39, p < 0.05) and lower sand content (r = -0.38, p < 0.05) enhances the wet-sieving aggregate stability of sandy loam. Frequent FTCs tend to improve wet-sieving aggregate stability but reduce dry-sieving aggregate stability in the sandy loam. The findings provide certain guidance for preventing freeze-thaw-induced wind erosion.