42 Years of straw incorporation drive macroaggregation, enhancing macropores and POM in a Vertisol: Insights from X-ray μCT

• X-ray μCT revealed 3D macropores and fresh/decomposed POM within aggregates. • 42-year straw incorporation + NPK increased SOC, GRSP and MBC in a Vertisol. • Straw-driven binding agents promoted 3–5 mm macroaggregates and higher MWD. • High straw increased surface-connected porosity by 230% and connectivity by 94.6%. • High straw increased fresh and decomposed POM densities by 281% and 93.9%, respectively. Soil macropore structure plays a critical role in the accumulation of fresh and decomposed particulate organic matter (POM). However, how long-term straw incorporation affects aggregate stability, as well as the dynamics of POM and aggregate pore structure, through its influence on soil binding agents, remains unclear. This study investigated the effects of four decades of distinct fertilization regimes on POM accumulation, macropore structure, and aggregate stability in Shajiang black soil (Vertisol). The regimes comprised no fertilization (Control), chemical fertilization alone (NPK), and chemical fertilization combined with either half (NPKLS) or full (NPKHS) straw incorporation. Using X-ray computed tomography, we quantified macropore characteristics and POM within aggregates, along with key soil binding agents, including glomalin-related soil protein (GRSP), soil organic carbon (SOC), and microbial biomass carbon (MBC). Our results showed that compared to control, straw incorporation (NPKLS, NPKHS) significantly increased GRSP by 57.6%-81.6%, SOC by 34.3%-51.7%, MBC by 69.2%-131%. This enhancement contributed to the formation of large macroaggregates (3–5 mm) and improved aggregate stability. Furthermore, the NPKHS significantly increased aggregate surface-connected porosity, isolated porosity, and connection probability by 230%, 166%, and 94.6%, respectively ( P < 0.05). It also increased the volume density of both fresh and decomposed POM within aggregates by 281% and 93.9% ( P < 0.05). In summary, carbon input from straw incorporation enhanced the formation of soil binding agents, which facilitated the development of 3–5 mm macroaggregates. Long-term chemical fertilization combined with full straw incorporation is an effective strategy for enhancing POM accumulation, improving macroaggregate pore structure, and increaseing aggregate stability in Vertisols.