Topsoil and subsoil distribution of soil properties in an agricultural area

Soil health monitoring aims mostly topsoil (0-30 cm), resulting in a knowledge gap in the subsoil properties. Accurate predictions of soil organic carbon (SOC) stocks require understanding subsoil characteristics, however, the high cost of new sampling campaigns highlights the importance of existing legacy soil data, which remain underdeveloped. Harmonized these legacy datasets, including digitization and standardisation of methods, can enhance their applicability. This study deployed legacy data from a 1991 soil survey in the intensively cultivated agricultural region of Karditsa, Greece, to investigate variations in subsoil properties (organic matter, pH, CaCO₃, cation exchange capacity (CEC), clay, and silt) across various depths (0-30, 30-60, 60-90 cm). Relationships between these properties, vegetation indices (NDVI), and geomorphological factors (elevation, aspect) derived from remote sensing were also analysed. Results revealed significant depth-dependent decreases in organic matter and silt, alongside increases in pH, CaCO₃, and clay content. Notably, clay was correlated positively with organic matter and CEC but negatively with silt at intermediate depths. Elevation exhibited weak to significant negative correlations with silt, CaCO₃, and NDVI, particularly at 30-60 cm, while aspect showed no significant relationships. These findings highlight the integration of legacy data and remote sensing to advance subsoil monitoring in the Mediterranean region, as demonstrated by the PRIMA SOILS4MED project. Abstract submitted to the "Soil Health: Current Status and Future Needs Conference".