Soil carbon and nitrogen storage and biomass carbon reserves in silvopastoral systems of the subhumid tropics of Mexico

Abstract

The conversion of natural vegetation, such as forests, to full-sun pasture diminishes soil carbon (C) and nitrogen (N) stocks. Silvopastoral systems (SPS) are considered a viable alternative, as they contribute to carbon sequestration and nitrogen retention in soils and biomass. This study aimed to evaluate soil C and N stocks, along with C in tree biomass, in SPS with scattered trees in pastures (STP), monoculture pasture (PM), and dry forest (DF) in the sub-humid tropics of Mexico. Tree biomass (for trees with a diameter ≥10 cm) was estimated using an allometric model to determine the biomass C content. Soil C and N stocks were determined for five depth classes (0–10, 10–20, 20–30, 30–40, and 40–50 cm). Correlations between soil physicochemical properties and C and N stocks were analyzed. Furthermore, total C stocks (tree biomass and soil) were estimated for the three systems. The results indicated that DF exhibited a greater proportion of woody species with diameters of 10–30 cm and heights of 5–15 m than STP, storing the highest biomass C stock (72.6 Mg ha^–1). The DF and STP systems had higher C and N stocks than PM. The highest C and N stocks were found in the surface stratum (0–10 cm) compared with the other strata in all systems. However, soil C and N stocks (0–50 cm) in STP (113.3 Mg C ha^–1 and 16.1 Mg N ha^–1) were similar to DF (119.1 Mg C ha^–1 and 15.5 Mg N ha^–1). In contrast, total C stocks was highest in DF (191.7 Mg C ha^–1), followed by STP (122.9 C ha^–1) and the lowest in PM (81.7 Mg C ha^–1). Soil physicochemical properties showed distinct correlations with C and N stocks, depending on the land-use system. We conclude that the conservation of DF and the implementation of SPS, such as STP, are key strategies for preserving soil C and N stocks in areas with high pressure of land conversion for livestock production.