Soil carbon and bulk density distribution within 10 Southern Piedmont grazing systems

Abstract

Sufficient and consistent distribution of carbon (C) across pastures can influence and improve production and sustainability in pasture-based grazing systems. The objective of this research was to determine spatial distribution of bulk density, soil C measured as loss-on-ignition (LOI) C, and permanganate oxidizable C (POXC), in continuously stocked Southern Piedmont pastures as affected by landscape position and management to enable producers to make better informed management decisions. Soil samples were collected from three depths (0 to 5, 5 to 10, and 10 to 20 cm), on a 50 m grid (matrix) and within areas of interest (AOIs, where cattle tended to frequent) from 10 pastures (ranging from 9.2 to 21.8 ha) fertilized with only mineral fertilizer. Mean soil bulk density was greatest (μ = 1.62 g cm⁻³) in the 5 to 10 cm soil layer. Median soil LOI and POXC were greatest in the 0 to 5 cm soil layer (medians = 6.16 g kg⁻¹ and 776 mg kg⁻¹, respectively), and both were strongly correlated to soil organic C. Soil phosphorus (P) was lowest in the 10 to 20 cm samples (median = 2.12 mg kg⁻¹), regardless of sampling location. Multivariate analysis of variance (MANOVA) determined that bulk densities were lower closer to hay and water sources (usually within 0 to 39 m from sources) not located in areas vulnerable to erosion likely because of added C combined with the moderate hoof action to incorporate C into the soil. However, LOI values in the surface 0 to 5 cm soil layer associated with hay, water, and shade in areas vulnerable to erosion demonstrated relatively few differences in distance from a hay, water, or shade source, and these differences often did not occur until 200 m or greater from a pasture equipage. This research indicates that producers can more efficiently utilize nutrient resources and improve soil health measures with strategic placement of hay, waterers, or shade to facilitate best use of limited resources.