Soil Nitrogen Distribution Mediated by Soil Organic Matter in Traditional and Irrigated Olive Systems under Mediterranean Conditions

Olive-based agroecosystems dominate large areas of the Mediterranean basin and play a key role in regional food production and rural livelihoods. Nitrogen (N) availability is a central determinant of olive productivity and environmental sustainability.  Its spatial and vertical distribution in olive grove soils remains poorly characterized, particularly across contrasting management systems. Because SOM constitutes the main reservoir and regulator of soil N, understanding N dynamics requires explicit consideration of SOM patterns. This study investigates how SOM mediates soil N distribution in traditional rainfed and irrigated olive systems in Northern Morocco. Soil samples were collected at three depths (0–20, 20–40, and 40–60 cm) and at two positions relative to the tree (under the canopy and inter-row). Analyses focused on TN and its association with SOM, as well as P₂O₅, K₂O, CEC, soil moisture, and calcium carbonate. Results show that TN closely followed the SOM distribution across depths and positions in both systems. Traditional rainfed orchards (TM) exhibited consistently higher SOM and associated TN stocks than irrigated systems (IS), particularly under tree canopies and in surface layers. Surface SOM values in TM frequently exceeded 5%, corresponding to higher TN concentrations, while irrigated soils generally remained below 3% SOM and displayed lower TN levels despite increased soil moisture. Across both systems, TN decreased with depth, but TM maintained higher TN concentrations in subsoil layers, indicating greater vertical stability of ON pools. Strong positive relationships between SOM and TN, together with higher P₂O₅, K₂O, and CEC in SOM-rich zones.