Organic Carbon Influences on Soil Particle Density and Rheological Properties
2006
Blanco-Canqui, Humberto | Lal, R. | Post, W. M. | Izaurralde, R. C. | Shipitalo, M. J.
Soil particle density (ρₛ) is not routinely measured and is assumed to range between 2.60 and 2.70 Mg m⁻³ or to be a constant (2.65 Mg m⁻³) when estimating essential properties such as porosity, and volumetric water and air relations. Values of ρₛ for the same soil may, however, differ significantly from the standard range due to management-induced changes in soil organic carbon (SOC) concentrations. We quantified the ρₛ and Atterberg limits of a Rayne silt loam for five long-term (>22 yr) moldboard-plowed continuous corn (Zea mays L.; MP), no-till continuous corn (NT), no-till continuous corn with beef cattle manure (NTm), pasture, and forest systems. We also assessed the relationships of SOC concentration with ρₛ and the Atterberg limits and the impact of ρₛ on soil porosity. Mean ρₛ across NT, NTm, and pasture (2.35 Mg m⁻³) was ∼7% lower than that for MP in the 0- to 10-cm soil depth (2.52 Mg m⁻³, P < 0.01). Forest had the lowest ρₛ of all soils (1.79 Mg m⁻³). The NTm caused a greater reduction in ρₛ and a greater increase in SOC concentration, liquid limit (LL), plastic limit (PL), and plasticity index (PI) than NT. Surface soils under MP had the highest ρₛ and ρb and the lowest SOC concentration, LL, PL, and PI. The SOC concentration was correlated negatively with ρₛ (r ² = 0.75) and positively with Atterberg limits (r ² > 0.64) at >20-cm depth. Estimates of soil porosity for NT, NTm, and pasture using the constant ρₛ overestimated the “true” porosity by 12% relative to that using the measured ρₛ
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