Particle Density Variability of Selected Pedons and Catenas in Iowa.

Soil particle density is an important physical parameter often used to calculate porosity. Particle density varies with the mineral suite and organic content of the soil, but is generally assumed to be 2.65 g cm^-3. We examined seventeen benchmark Mollisol and Alfisol pedons from across Iowa, as well as four closed-basin catenas in north central Iowa, to determine the particle density distribution both within the profile and across the landscape.  Parent materials include hillslope sediment, eolian deposits, Late Wisconsinan loess, Late Wisconsinan till, and Pre-Illinoian till. We found that particle density increases with depth in some profiles but not others, and ranges from 2.12 – 2.71 g cm^-3 at the surface to 2.65 - 2.84 g cm^-3 at depth. In the catenas, particle density increases with depth and with distance from the basin center.  Overall, our particle density values vary systematically within profiles and across the landscape, calling into question the general assumption of a constant density. Furthermore, these findings show that particle density is an indicator of pedogenic processes and therefore the documentation of particle density will facilitate quantitative pedogenic modeling.