Microstructures in oxidic Oxisol under intensive cultivation

Intensive conventional cultivation leads to the deterioration of the original soil structural hierarchy. This study investigated the long-term impacts of irrigation and intensive management on the microstructural stability of an Oxisol (Typic Haplustox) across a 43-year chronosequence, in the 0–0.2 and 0.8–1.0 m layers. By integrating micromorphology, synchrotron-based X-ray microtomography (SR-μCT), and micro-chemical analysis (SEM-EDX), we show that cultivation promotes a systematic transition from stable coalesced blocks to individualized, degraded microaggregates. In the native vegetation (reference area), kaolinite acts as a primary agglutinating agent, maintaining a complex structural hierarchy of granular microaggregates. However, long-term liming and fertilization induce kaolinite dispersion, accelerating the breakdown of these blocks and the selective preservation of Al-Fe-rich aggregates. After 43 years of cultivation, the remaining microaggregates exhibit smaller sizes (0.7 mm) and higher roundness (≈ 1). Aggregate porosity increased due to the formation of new voids (32%), which are larger (7.75 μm), elongated (0.27), less connected (Euler number – 10993) and spherical (0.85) and lower tortuosity (1.79) in older cultivations. These findings demonstrate that intensive land use alters the microstructure starting from the first year of cultivation, promoting the selection of aggregates and the microstructural homogenization in the topsoil (0–0.2 m). • Intensive use alters the microstructure of the soil in the long term. • The blocks are fragmenting from coalescing structures in long-term by intensive use. • Kaolinite dispersion promotes microstructural homogenization. • Smaller, rounded Al/Fe aggregates selected over time under land use. • The intra-aggregate voids have larger, more elongated and less connected in long-term.