PNNL

Abstract

Soil particle density (rs) is not routinely measured and is assumed to range between 2.60 and 2.70 Mgm23 or to be a constant (2.65 Mgm23) when estimating essential properties such as porosity, and volumetric water and air relations. Values of rs for the same soil may, however, differ significantly from the standard range due to managementinduced changes in soil organic carbon (SOC) concentrations.We quantified the rs 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 rs and the Atterberg limits and the impact of rs on soil porosity. Mean rs across NT, NTm, and pasture (2.35 Mg m23) was |7% lower than that for MP in the 0- to 10-cm soil depth (2.52 Mg m23, P , 0.01). Forest had the lowest rs of all soils (1.79 Mg m23). The NTm caused a greater reduction in rs and a greater increase inSOCconcentration, liquid limit (LL), plastic limit (PL), and plasticity index (PI) than NT. Surface soils under MP had the highest rs and rb and the lowest SOC concentration, LL, PL, and PI. The SOC concentration was correlated negatively with rs (r 2 5 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 rs overestimated the ‘‘true’’ porosity by 12% relative to that using the measured rs.