Soil organic carbon (SOC) dynamics are increasingly recognized as a cornerstone of soil health and ecosystem resilience. Yet, limited knowledge exists on how seasonal fluctuations and management practices (e.g., cover crops) shape both stable and labile carbon pools in the root zone of Mediterranean orchards. This study assessed the effects of winter cover crops on total organic carbon (TOC), active carbon, and nitrogen in the root zone of a Mediterranean almond orchard over three years. Cover crop treatments included ryegrass (2023), a legume–cereal–brassica mix (2024), and spontaneous vegetation (2025), all of which were terminated in late February.
Significant treatment and seasonal effects were observed. Across the 0–90 cm profile, TOC increased by 15–20% under cover crops, especially in the 0–40 cm layer, suggesting enhanced long-term carbon sequestration. Spring TOC values were lower by 10–12% than fall values, suggesting a significant impact of tree roots. Active carbon was 30–45% higher in spring under cover crops. These contrasting trends underscore the different stability of carbon fractions: TOC reflects longer-term sequestration, whereas active carbon represents short-term energy availability for soil biota. Nitrogen also benefited, with cover crops improving retention by 20–25% in the top 0-40 cm layer, reducing potential losses under fertigation regimes. Overall, Tree-line cover crops improved soil carbon, nitrogen retention, and seasonal carbon cycling across soil depths. This regenerative approach supports soil health under Mediterranean conditions and offers resilience under growing resource constraints.
