Integrating Soil Compactness, Carbon Stocks, and Pieri-Index-Based Structural Vulnerability for Soil Quality Assessment Across Tropical Land-Use Systems

Integrated assessments combining soil compactness, carbon storage, and structural vulnerability remain scarce in tropical soils of the Colombian Orinoquia. Soil physical condition was compared across natural forest (n = 21), secondary vegetation (n = 27), agricultural use (n = 12), and improved pastures (n = 67) in Arauca, Colombia, using stratified purposive sampling. The 127 samples from the 0–30 cm layer were analyzed for pH, soil organic carbon (SOC), bulk density, and particle-size distribution. Texture-adjusted packing density, fixed-depth SOC stock, and the Pieri index were calculated. Comparisons used Kruskal–Wallis and Dunn’s tests with Holm adjustment and epsilon-squared (ε2) effect sizes. Soil pH and texture did not differ among categories. SOC stock differed significantly (p = 0.001, ε2 = 0.104), with a median of 56.5 Mg C ha−1 in natural forest and 30.0–35.3 Mg C ha−1 in the other categories. Higher SOC stock in natural forest coincided with higher SOC concentration despite lower bulk density, indicating that stock differences were associated with carbon concentration rather than texture. The Pieri index also differed (p = 0.002, ε2 = 0.095), with lower inferred structural vulnerability in natural forest. Packing density showed a weaker association with land use (PD-R: p = 0.041, ε2 = 0.043), with no significant pairwise differences after Holm adjustment. Because the study was cross-sectional and observational, these differences should not be interpreted as causal effects of land-use conversion. These findings indicate that management and restoration assessments should prioritize soil organic matter status while using compactness indicators to identify sites requiring further evaluation.