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.