<![CDATA[Abstract. Mahardika RY, Siregar HH, Nusantara RW, Azizu MN, Afner DP, Erdiandini I, Fadilla U. 2026. Soil organic carbon density across peat humification levels in the acrotelm. Asian J Agric 10 (2): g100227. https://doi.org/10.13057/asianjagric/g100227. Tropical peatlands are major carbon stores, yet Soil Organic Carbon (SOC) density within the acrotelm may vary with peat decomposition and humification. This study compared volumetric SOC density and selected physicochemical properties between Hemic and Sapric peat in shrubland and an abandoned smallholder rubber plantation in West Kalimantan, Indonesia. Twenty peat samples, comprising 10 Hemic and 10 Sapric samples collected from paired acrotelm profiles, were classified using the von Post scale. SOC density was calculated from bulk density and LOI-derived SOC concentration and evaluated using resampling-based inference, effect-size estimation, quantile comparisons, variability analysis, Spearman correlations, and exploratory Principal Component Analysis (PCA). Sapric peat had higher SOC density (65.74 ± 13.77 kg C m-³) than Hemic peat (41.34 ± 6.97 kg C m-³), with a mean difference of 24.41 kg C m-³, permutation p = 0.0003, and Hedges’ g = 2.14. Sapric peat also had greater bulk density (0.125 vs 0.076 g cm-³), whereas SOC concentration differed only modestly (52.63% vs 54.30%). SOC density remained higher in Sapric peat across Q20-Q80, while evidence for greater variability was weak (CV ratio = 1.24, 95% CI 0.48-3.00; Fligner-Killeen p = 0.118). PCA showed partial separation primarily along PC1 (51.3%). These results provide site-specific evidence that humification-associated differences in peat structure, particularly bulk density, are related to volumetric SOC-density patterns at the investigated sites. Broader applicability requires validation across independently replicated peatlands and hydrological conditions.]]>
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