Soil carbon concentrations are highly variable spatially. Measures of variability usually consider horizontal variance in a plot, field, or landscape. Soil C also varies vertical, however, such as down a soil profile. Here I quantify variance on soil pit faces capturing both fine scale (10 cm) horizontal and vertical variance. I hypothesized that variance in soil pit faces would vary with land cover as a result of time since disturbance and extent of rooting. As such, soil C structure in pit faces should be greatest in relatively undisturbed hardwood forests, slightly less in aggrading pine forests, and lowest in agricultural fields. At the Calhoun Critical Zone Observatory in the USA’s Southern Piedmont we excavated soil pits under each land use with 2 to 4 replicates. We used visible/near infrared reflectance spectroscopy to measure soil C on a 50 cm wide by 150 cm deep grid using a cyclical sampling design. Each face included 35 to 40 samples with a minimum distance of 10 cm and a maximum of 150 cm. Semi-variogram analysis that was anisotropic given general declines with depth did not indicate strong differences in spatial structuring of soil C between land uses.
Markewitz, D., L. Sutter, D. Richter (2019): Soil C Spatial Variance within Soil Profile Pit Faces Under Three Land Uses As Measured By VNIRS. ASA-CSSA-SSSA International Annual Meeting, 10-13 Nov. 2019, San Antonio, Texas.
This Paper/Book acknowledges NSF CZO grant support.