Long-term structural changes in oxidic Latosols under intensive agricultural cultivation and irrigation

Soils with inherently high structural stability, such as highly clayey oxidic Latosols, are generally considered resistant to degradation; however, intensive and irrigated cultivation may compromise their aggregate stability. This study aimed to evaluate structural changes in these soils, addressing a knowledge gap on the long-term impacts of irrigated intensive agriculture on the physical resilience of oxidic tropical soils. Aggregate stability was assessed by wet sieving and sonication using aggregates of 4.75-2.00 mm, complemented by scanning electron microscopy analyses. Samples were collected from native Cerrado vegetation and cultivated areas with 1, 17, 22, 28, 32, and 43 years of intensive use, at depths of 0-0.2 and 0.8-1.0 m. A systematic design was applied, and ANOVA and regression analyses were performed considering the Cerrado as the reference (time zero). Both methods revealed significant losses in aggregate stability under irrigated cultivation, particularly in older fields (32 and 43 years). Wet sieving indicated a reduction in macroaggregates (-43.3 %) and an increase in mesoaggregates (+60.4 %) and microaggregates (+64 %) over time. Sonication confirmed the highest stability in native soils and the lowest in the 1-year cultivated area, where the methods yielded contrasting results. These findings demonstrate that intensive irrigated cultivation leads to long-term degradation of aggregate stability, with the greatest structural disruption occurring in the first years of use. The study indicates that the mean weighted and geometric mean diameters obtained by the wet sieving method were not efficient indicators of aggregate stability for oxidic soils.