Comparative effects of tillage methods and depths on soil aggregate stability and organic carbon in sugarcane fields

To assess the effectiveness of Smash-Ridging Tillage in improving soil structure and fertility, this study compared the impacts of traditional rotary tillage at 20 cm depth and Smash-Ridging Tillage at depths of 20 cm and 40 cm (F40) on soil aggregate distribution and stability meanwhile with its soil organic carbon characteristics in sugarcane fields of Guangxi, China. The results demonstrated that Smash-Ridging Tillage significantly reduced soil bulk density and enhanced soil total nitrogen content. Notably, it markedly increased the proportion of water-stable macroaggregates (> 0.25 mm) (p < 0.05), with the F40 achieving the highest macroaggregate content (51.17-60.72%). Aggregate stability, as indicated by mean weight diameter (MWD) and geometric mean diameter (GMD), was also significantly improved under Smash-Ridging Tillage. Pearson correlation and redundancy analyses revealed that macroaggregate content and the contribution rate of organic carbon associated with macroaggregates were positively correlated with MWD and GMD, but negatively correlated with fractal dimension and soil erodibility factor. The F40 showed the highest contribution rate of macroaggregate organic carbon, which was approximately 20.58-32.57% higher than that under traditional rotary tillage. Overall, deep smash-ridging tillage at 40 cm significantly improved soil structural stability, which enhanced organic carbon stabilization within macroaggregates, providing a scientific reference for optimizing tillage practices to improve soil structure and organic carbon sequestration in subtropical sugarcane fields.