Landscape-scale soil C and N stocks assessment in contrasting olive systems.

Olive (Olea europaea L.) is of significant socio-cultural and dietary importance throughout the Mediterranean region. Its continuous net primary production sequesters CO2 in plant biomass and as soil organic carbon, improving soil health and sustaining the livelihood of smallholder farmers. However, soil carbon stock depends on the landscape position, soil properties, and management practices in the olive orchard. This work evaluates soil carbon and nitrogen stocks across a landscape of both intensively managed and traditional olive orchards in Ouazzane province, northern Morocco. The on-farm experiment is located in typical olive groves at two elevations 108 m apart, with 3 sites selected in traditional olive orchards at the summit and 3 sites in irrigated orchards at the toe-slope of the landscape. Soil samples were collected in February 2025 under the tree canopy and midway between tree rows, at depths of 0-10, 10-20, 20-40 and 40-60 cm. Soil samples were dried (<50 °C) and analyzed for total carbon (TC), total organic carbon (SOC), total inorganic carbon (SIC), and total nitrogen (TN). Olive groves at the summit averaged 4.5% TC and 2.5% SIC, whereas irrigated orchards at the toeslope had a mean of 1.5% TC and 0.3% SIC. There tends to be more SOC and TN under the tree canopy than in the inter-row area. This suggests that SIC stocks developed through pedo-climatic processes whereas SOC and TN stocks were influenced by tree canopies and agricultural management. The implications for quantifying soil carbon stocks in olive orchards will be discussed.