Effects of Crop Sequences and Fertilization Regimes on Soil Bulk Density Profiles In a Long-Term Experiment Under Conventional Tillage In Central Pennsylvania.

The assessment of soil bulk density under different cropping systems is a comparatively rapid and cost-efficient way to evaluate cumulative changes in soil properties due to applied cropping systems. Moreover, precise measures of depth-wise bulk density profiles over the existing natural soil variability are needed to estimate and extrapolate soil carbon concentrations to larger scales in studies of soil carbon sequestration. We characterized soil bulk density by depth in a 40-year-old crop management trial having 192 plots containing 4 field block replicates representing 16 combinations of crop sequences and three soil fertilization practices. We sampled one soil core (nominally 5.9-cm diameter x 1 m in length) from each plots using a tractor mounted hydraulic probe. The bulk density was determined for 10 soil segments per soil core at 10 cm depth increments. We hypothesize that depth-wise variation in bulk density profiles will be strongly influenced by rotation and fertilization method. Furthermore we suspect that observed patterns and trends will be associated with known traits of the applied cropping systems, including relative numbers of tillage and field passes, residue cover, and presence of live roots over time and at each depth. The soil bulk density profiles were found to be influenced by soil depth, followed by rotation, fertilization method, landscape position and interaction effects. The presentation will report how much of the differentiation in bulk density profiles within the long-term trial is explained by the applied treatments, and the degree to which the variation can be associated with the suspected agronomic factors.