Soil Carbon Sequestration in Nothofagus obliqua Forests with Different Canopy Cover Levels under Silvopastoral Management

Agroforestry contributes to slowing deforestation, favouring ecosystem regeneration and improving land use sustainability. In this study, we evaluated the effect of agroforestry on the recovery of degraded soils in a native forest and its capacity to capture and stabilize carbon (C) and nitrogen (N) in the soil. We conducted the study in a native forest of Nothofagus obliqua (oak) located in Ranchillo Alto (37°04′52″ S, 71°39′14″ W), in the Ñuble region, Chile. This site includes three silvopastoral systems with different levels of forest degradation: open (Op), semi- open (SOp) and semi-closed (SC), together with a control treatment without silvopastoral treatment (Ctr). The analysis was conducted at four soil depths (0-10, 10-20, 20-30 and 30-60 cm). To evaluate carbon and nitrogen sequestration and fixation in relation to the different forest cover treatments, we performed chemical, physical and biological soil analyses. We also included a physical fractionation by particle size to separate soil organic matter (SOM) into meaningful fractions with different characteristics and dynamics: particulate organic matter (POM) and organic matter associated with the mineral matrix (MAOM). Our results indicated that Op, despite being the most degraded condition, showed the highest values of C, N and non- oxidizable carbon (Cnox). This condition could be associated with the history of potato burning in this sector, which generates stable pyrogenic carbon in the soil. Analyses of C and N, as well as Cnox in the MAOM fraction, and C stock revealed that the three silvopastoral systems showed higher values than the control treatment without silvopastoral treatment. This suggests that the adoption of silvopastoral practices can improve soil quality and contribute to long-term carbon sequestration. These results support the application of sustainable practices to mitigate soil degradation and enhance carbon sequestration in degraded ecosystems.