Soil organic carbon stocks, litter decomposition, and soil macrofauna diversity across contrasting land uses within a dual-purpose cattle farm in the Colombian Amazonian foothills.

Abstract

Silvopastoral systems and other tree-based land uses are increasingly promoted for soil conservation and climate-change mitigation in tropical livestock landscapes. However, their relationships with soil organic carbon (SOC), litter decomposition, and soil macrofauna remain poorly characterized in Amazonian production systems. In this single-farm case study, we assessed SOC distribution and stocks, soil bulk density (ρb), early litter decomposition, and soil macrofaunal communities across five contrasting land-use sites in the Colombian Amazonian foothills. The silvopastoral site had been established 18 months before sampling, allowing characterization of its early-stage soil conditions. Depth-stratified sampling showed pronounced SOC enrichment in the 0-10 cm layer at the silvopastoral site, which also had lower overall ρb than open pasture (1.29 vs. 1.48 g cm-3). However, SOC stocks from the independently sampled 0-30 cm profile were comparable between these sites. Cumulative litter mass loss increased during the 60-day evaluation and varied among forage species and sites, whereas C and N concentrations and C:N showed no statistically supported temporal changes. Macrofaunal organization varied among sites and soil depths; the silvopastoral site had the highest observed Shannon diversity in the 0-10 cm layer (H' = 1.14), although no site consistently showed the greatest diversity and evenness across all depths. Overall, the silvopastoral site combined favorable surface soil attributes with comparatively high upper-layer macrofaunal diversity. Given the cross-sectional design and single-site representation of each land use, these findings constitute a baseline characterization of site-specific conditions rather than evidence of changes attributable to silvopastoral establishment.