Soil Quality Under Poplar and Agricultural Management.

Woody bioenergy feedstock production in United States has been increasing, however, there is little information on how these management practices impact surface soil chemistry. In order to understand the soil processes under poplar (Populus spp.) trees and adjacent agricultural sites, surface (0-15 cm) soil samples were collected from four northwestern United States locations over time. Initial and final surface soil samples were analyzed for various soil chemical parameters including organic matter, pH, cation exchange capacity and nutrient concentrations. Fields selected to compare poplar and agricultural management initially differed in some key soil chemical parameters. Many soil chemical parameters changed over time and the magnitude of changes often depended on location; however, initial differences between management types within any one location did not change over time. Consistent in-location differences between management types over time show poplar did not alter soil chemical parameters relative to agricultural management during the study period. Soil samples collected from deeper profile indicated that nitrate-N was probably taken up by poplar or, agricultural root systems by up to 77% compared to surface soil. Estimated phosphorus saturation ratio (PSR) of the studied soils could be impacted by P beyond 0.5, and 1.0 PSR for the soils with > 10%, and < 10% organic matter, respectively. Additionally, lysimeter water samples were also collected, and analyzed for various nutrients over time under different management to understand nutrient leaching. Together all of the observations indicate that only little of the overall soil chemistry was impacted by introduction of poplar in the traditionally agricultural fields. The synthesized knowledge from this study may help producers, land owners, and policy makers to take decision on continuous poplar production in the studied sites.