Redistribution of major mineral-forming elements (Fe, Al, Si, Mn) and nutrient-associated trace elements (Cu, Zn, P) following rice-to-pomegranate land-use conversion in Southern Italy

Aims This study explores the geochemical consequences of converting long-term flooded rice fields to non-flooded pomegranate orchards in calcareous, organic-rich soils of Southern Italy. Methods By analyzing topsoil (0–20 cm) and subsoil (50 cm) samples, we investigated how land-use change influences the distribution, speciation, and mobility of iron, copper, zinc, manganese, aluminum, phosphorus, and silicon. Sequential extraction, Mössbauer spectroscopy, and elemental analyses were employed to assess shifts in redox-sensitive mineral phases and nutrient pools. Results The transition to aerobic conditions induced substantial alterations in iron fractionation, including the loss of amorphous and acid-soluble phases and increased crystallization into more stable reducible forms. Despite these structural changes, Mössbauer spectroscopy revealed that iron redox states remained largely unaffected, indicating strong valence-state resilience. Copper became more strongly associated with manganese and (amorphous) iron oxides, while its acid-soluble fraction declined significantly, particularly in the subsoil. In contrast, zinc remained largely immobilized within the residual fraction, demonstrating greater geochemical stability. Conclusions Our findings underscore the complex interaction between redox conditions, mineral transformations, and nutrient dynamics during land-use transitions. Understanding these processes is critical for managing soil fertility and minimizing environmental risks in Mediterranean agroecosystems.