Quantifying and visualizing soil macroaggregate pore structure and particulate organic matter in a Vertisol under various straw return practices using X-ray computed tomography

The structure of soil pores plays a crucial role in determining the distribution and retention of particulate organic matter (POM) within soil aggregates, yet the specific effects of different straw return practices on POM stabilization through soil pore structure remain poorly understood. This study aimed to quantify and visualize soil macroaggregates POM distribution and pore structure using advanced X-ray computed tomography (CT) and image processing techniques under three straw return practices: no-tillage with straw mulching (NTS), traditional rotary tillage with straw incorporation (RTS), and deep plowing with straw incorporation (DPS) in a Vertisol. A total of 27 soil aggregates (4–6 mm) from soil depths of 0–10, 10–20, and 20–40 cm were analyzed at an 8-μm resolution. The results showed that NTS significantly increased POM content and surface area density in the 0–10 cm soil layer compared to RTS. In contrast, DPS was most effective in deeper soil layers (20–40 cm), maintaining high POM content and promoting the development of extensive and well-connected pore networks, as evidenced by significantly higher connected porosity and mean breadth density of POM. Additionally, strong positive correlations were observed between POM content, connected porosity, and pore connectivity (P < 0.05). These findings highlight the importance of selecting appropriate straw return practices to optimize POM retention and enhance soil C storage, particularly in the context of sustainable soil management in Vertisols.