RCCZO -- Geology, Soil Biogeochemistry, Soil Texture -- Lithology, Coarse Fraction, Bulk Density & TOC -- Reynolds Creek Experimental Watershed -- (2014-2016)

Pedotransfer functions (PTFs) have been developed to estimate soil bulk density (BDFF) using the relationships with soil organic carbon content (SOC) and particle size distribution. Current PTF’s implicitly assume that coarse fraction (CF) content and lithology do not influence BDFF. In this study, we examine the influence of CF content and lithology on BDFF estimates by developing PTF’s for total bulk density (BDT), which includes both fine and coarse fragments, using measured SOC in soils derived from felsic and mafic lithologies (148 felsic and 64 mafic, 212 total). Our results show that SOC is highly correlated with BDT in soils derived from felsic (r2 value of 0.79, p2 value of 0.84, p 2 mm), and we adjust BDT with soil pedon CF content to determine fine fraction bulk densities (BDFF-CFadj). A validation subset of 70 samples was used to compare our model against 23 published PTFs. When BDT is corrected for CF, which is highly variable vertically and horizontally within the watershed, we observe substantial improvements (average of 10.05 ± 4.89 %) in BDFF-CFadj estimation and associated errors compared to other PTFs. Findings from our study demonstrate that incorporation of CF and lithology into BDFF estimations can substantially improve BDFF and consequently soil carbon stock estimates.土壤传递函数（Pedotransfer Functions，PTFs）是一类借助土壤有机碳（Soil Organic Carbon，SOC）含量与粒度分布的相关关系，估算细粒土壤容重（BDFF）的方法。现有PTFs默认粗粒组分（Coarse Fraction，CF）含量与岩性不会对BDFF产生影响。本研究针对源自长英质与镁铁质岩性的土壤（共212份样本，其中长英质148份、镁铁质64份），通过实测SOC构建适用于总容重（BDT，包含细粒与粗粒碎屑）的PTFs，以此探究CF含量与岩性对BDFF估算的影响。研究结果显示，SOC与长英质岩性土壤的BDT呈高度相关（r²=0.79，p<0.001），与镁铁质岩性土壤的BDT相关性同样显著（r²=0.84，p<0.001）；针对粒径大于2mm的土壤，我们通过土壤剖面CF含量对BDT进行校正，以得到细粒组分容重（BDFF-CFadj）。我们选取70个样本作为验证子集，将本研究构建的模型与23篇已发表的PTFs开展对比。当针对流域内空间与垂向变异极强的CF对BDT完成校正后，相较于其他PTFs，BDFF-CFadj的估算精度与相关误差表现均得到显著提升（平均提升幅度为10.05±4.89%）。本研究结果证实，将CF与岩性纳入BDFF的估算流程，可显著优化BDFF的估算精度，进而提升土壤碳库的估算结果。