Objective The aims were to clarify the composition, stability characteristics and main influencing factors of different saline soil aggregates in the Yinbei area of Ningxia, and to provide scientific basis for the quality evaluation and structural improvement of saline soil in the region.

Method The mechanical stable and water-stable aggregate composition of non-saline, slightly, moderate, heavy saline soils and saline soils in the Yinbei area were determined using dry screening and wet screening methods.

Result The distribution of mechanical stable aggregates in soils with different degrees of salinization in the Yinbei area was mainly in the > 2 mm aggregates (average 78.73%), with the lowest content in the < 0.25 mm aggregates (average 2.92%). The contents of aggregates did not show a regular change due to the degree of salinization < 0.25 mm water-stable aggregates account for 94.23%. With the increase of soil salt content, the contents of water-stable aggregates in 0.25 ~ 2 mm (except for moderately saline soil) and 0.053 ~ 0.25 mm gradually decreased, while the contents of < 0.053 mm particle size gradually increased. The average weight diameter (MWD_d) of mechanical stable aggregates in saline soil is significantly higher than that of water-stable aggregates (MWD_w). The MWD_d of saline soil was significantly lower than that of other soils (P < 0.05). The variation trend of the geometric mean diameter (GMD_d) of mechanical stable aggregates with different degrees of salinization was consistent with MWD_d. The geometric mean diameter (GMD_w) of water-stable aggregates and the contents of aggregates > 0.25 mm (WR_0.25) gradually decreased with the aggravation of salinization (except for severe WR_0.25). The erodible factor (K_d) and fractal dimension (D_d) of mechanical stable aggregates in saline soil were significantly higher than those in soils with other degrees of salinization (P < 0.05). The non-saline soil water stable soil had the lowest erodible factor (K_w) and fractal dimension (D_w). The destruction rate (PAD) of non-saline soil aggregates was the smallest, while the PAD of saline soil was the largest. The contents of water-stable aggregates between 0.25 ~ 2 mm and < 0.053 mm were generally significantly correlated with the basic physical and chemical indicators of soil. The MWD_w, WR_0.25, and GMD_w of water-stable aggregates were significantly or extremely significantly negatively correlated with salt content, pH and Na ⁺ , and significantly or extremely significantly positively correlated with organic matter and nutrients, while the correlations among K_w, D_w and PAD with various soil indicators were generally opposite to the relationship between MWD_w and various indicators.

Conclusion With the increase of soil salinity, the contents of water-stable aggregates ranging from 0.053 ~ 2 mm gradually decreases, while the contents of < 0.053 mm aggregates gradually increases. The degree of salinization, organic matter and nutrient content significantly affect the composition, stability and erodibility of soil water stable small and microaggregates in the Yinbei area of Ningxia.