Crop Litter Has a Strong Effect on Soil Organic Matter Sequestration in Semi-Arid Environments

The agricultural soils in the Mediterranean are characterized by low stocks of soil organic matter (SOM) because of the intensive management practices and constraints on litter inputs to the soil imposed by environmental conditions (low precipitation, high evapotranspiration). To date, several studies have provided evidence for a low potential of Mediterranean agroecosystems, especially on its southern part, to store C, even under soil conservation practices (e.g., non-tillage), questioning the capacity of commonly applied practices to restore soil health, mitigate climate change and improve resilience of agroecosystems to climate extremes. Using paired orchards of avocado and olive trees, we show that soils in the South Mediterranean have a high potential for C storage that depends strongly on crop type and soil properties. Soils planted with avocado trees showed higher SOM contents compared to olive trees mainly in the upper soil layer (0–10 cm) which were linked to higher inputs and litter chemistry. Our findings enable us to re-define achievable thresholds of SOC (≈8%) in Southern Mediterranean soils to store C, to quantify the effect of different cropping systems, and the period required to reach this potential and how this potential is affected by soil properties. Thus, the findings have profound implications for the design of soil conservation practices compatible with Mediterranean conditions and developing initiatives describing achievable targets of SOM restoration depending on soil properties and cropping systems.