Physical properties and associated ecosystem services of Oxisols from Brazilian biomes as influenced by soil structure and mineralogy

Oxisols are the most weathered-leached soils in the world, containing quartz and muscovite in the coarse fractions, while in the clay fraction, kaolinite, goethite, hematite, and gibbsite, in different proportions, largely predominate, which strongly influence soil properties, particularly the structure. This study aimed to: (1) evaluate how variations in clay fraction mineralogy influence soil structure, physical properties, and derived-ecosystem services in Oxisols across different biomes of Brazil; (2) evaluate the performance of five machine learning algorithms to predict soil physical properties; and (3) analyze the differences and similarities between soils from temperate climate regions and Brazilian Oxisols at this respect. A dataset comprising soil physical and chemical properties, and clay mineralogical composition from B horizon of Oxisols was analyzed using linear correlation and principal component analysis. Despite the high variability observed among the evaluated soils, the clay fraction mineralogy strongly controls soil structure and its associated physical properties. Oxisols with higher contents of gibbsite in the clay fraction tend to develop granular structure, resulting in greater macroporosity, lower bulk density, and higher saturated hydraulic conductivity, whereas kaolinite-rich Oxisols were associated with block structure, higher microporosity, and lower permeability values. The soil structure plays the main role in the ecosystem functions of Oxisols from different Brazilian biomes. In terms of prediction models, the extreme gradient boosting (XGB) model was the most efficient for predicting soil attributes in Oxisols, where soil texture and structure were the most important predictors, followed by clay fraction mineralogy. In Brazilian Oxisols, structure is more important than texture in influencing their physical properties. According to the authors’ knowledge, this behavior is unique in terms of soil classes worldwide. Compared to temperate climate soils, Oxisols exhibit lower bulk density and higher macroporosity values, driven by intense weathering in tropical zone that promotes a unique relationship between gibbsitic clay mineralogy and microgranular structure.