Abstract:

This study employed a single-factor randomized block design with six treatments: control (CK), microalgal nutrient solution (WZ), desulfurization gypsum (SG), fulvic acid (HFS), organic fertilizer (YJF) and biochar (SWT). Combining field plot experiments with laboratory analysis, the research aimed to investigate the effects of different amendments on soil organic carbon (SOC) fractions and aggregate stability in saline-alkali soil of the Qaidam Basin. The improvement efficacy of the amendments was evaluated based on SOC fractions and aggregate stability. The results showed that biochar application significantly enhanced SOC fraction contents. The SOC, particulate organic carbon (POC), mineral-associated organic carbon (MAOC) and easily oxidizable organic carbon (EOC) contents under the SWT treatment were significantly higher than those under other treatments, reaching to 8.25, 2.00, 3.11 and 2.85 g/kg. Compared with the CK treatment, these values were increased by 112.53%, 282.19%, 70.13% and 203.19%, respectively. Fulvic acid application effectively increased the proportion of water-stable aggregates in the 0.053-0.25 mm and >0.25 mm size classes, showing increases of 17.89% and 7.14 % compared to CK. Furthermore, the HFS treatment yielded the highest mean weight diameter (MWD) and geometric mean diameter (GMD) values among all treatments, at 7.131 mm and 0.089 mm. These values were 5.69% and 18.67% higher than those of the CK treatment. Correlation analysis indicated no significant relationship between SOC fractions and either the composition or stability of water-stable aggregates. SOC and EOC showed a positive correlation with the content of aggregates <0.053 mm, but a negative correlation with the contents of 0.053-0.25 mm aggregates, >0.25 mm aggregates, MWD and GMD. In conclusion, biochar application facilitated SOC accumulation, while fulvic acid application promoted soil structural improvement.

Key words: soil amendments, saline-alkali soils, organic carbon fractions, aggregate stability