Genesis and properties of representative Ferralsols from the Brazilian Cerrado of Piauí

Ferralsols cover substantial areas in tropical regions, yet their pedogenesis on sedimentary rocks remains insufficiently understood. This study aimed to characterize the morphological, physical, chemical, and mineralogical properties of five representative sandy-textured Ferralsols developed in the Cerrado of the state of Piauí, Brazil, while assessing low-frequency magnetic susceptibility (χ lf ) as a auxiliary pedogenic proxy. Soils samples collected across identified horizons for routine physical, chemical, and mineralogical analyses. Results show predominantly coarse textures (sand content from 541.4 to 909.1 g·kg − 1 ), with kaolinite (Kt) dominating the clay fraction and quartz dominating the sand fraction. Chemical properties revealed strongly acidic condition (pH from 4.3 to 5.4) and low cation exchange capacity (CEC from 0.9 to 12.3 cmol c ·kg − 1 ). Weathering indices (Ki < 1.4; Kr < 1.0) indicate moderate weathering intensity, with no gibbsite detected. The studied soils exhibited low χ lf (< 10 × 10 − 8 ·m 3 ·kg − 1 ), with no correlation with other soil properties. Sandy Ferralsols from Piauí exhibit low nutrient retention capacity and high aluminum saturation, are moderately weathered, with quartz predominance in the sand fraction and Kt predominance in the clay fraction. The low χ lf values, uncorrelated with soil properties, confirm the limited ferrimagnetic content in these quartz-dominated systems, establishing χlf as a complementary rather than standalone pedogenic proxy.