Long-term mulched drip irrigation enhances the stability of soil aggregates by increasing organic carbon stock and reducing salinity.

Soil aggregate stability is critical to ensure the provision of agricultural land. Mulched drip irrigation (MDI) is widely used in arid region of northwest China, but the response of soil aggregate stability to soil organic carbon (SOC) and salinity as affected by continuous MDI is still unclear. In this study, we examined four MDI ages (9, 13, 15, and 23 years) of cotton fields that were converted from wasteland (CK, 0 year) and evaluated the impact of MDI age on soil aggregate size distribution, aggregate stability, and aggregate-associated SOC/salinity. The results showed that the proportion of macro-aggregates (>0.25 mm) and aggregate stability (MWD, GMD) initially decreased and then increased as MDI age progressed. As MDI age increased, the concentration of aggregate-associated SOC in all fractions significantly increased, while salt concentration significantly declined. Compared to the CK (0 year), the total SOC stock in cotton fields aged 9, 13, 15 and 23 years increased by −0%, 11%, 17%, and 87%, respectively; whereas the total salt stock decreased by 33%, 68%, 67%, and 76%, respectively. Moreover, due to the significant increase in macro-aggregate content and associated SOC concentration with MDI age, the storage of SOC in older MDI ages (15–23 years) was more reliant on macro-aggregates. Pearson correlation and principal component analysis indicated a negative correlation between salinity and macro-aggregates, aggregate stability, and SOC, while there was a positive correlation among MDI age, SOC, macro-aggregates, and aggregate stability. Based on our findings, we concluded that long-term MDI promotes the formation of macro-aggregates, enhances aggregate stability by reducing soil salinity and increasing SOC stock. • Long-term MDI strongly affects soil aggregate characteristics. • Long-term MDI significantly increased SOC stock and decreased soil salt stock. • SOC and salinity are key factors affecting macro-aggregates formation under MDI. • SOC storage is primarily dependent on macro-aggregates under long-term MDI. [ABSTRACT FROM AUTHOR]