ARS | Publication request: Switchgrass influences soil biogeochemical processes in dryland region of the Pacific Northwest

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 2012
Publication Date: N/A

Interpretive Summary: Switchgrass and other warm-season grasses are fast growing and can be made into a fuel for cars. However, long-term removal of biomass of this crop might deplete organic matter in the soil. This study evaluated how the soil would change when the biomass of switchgrass was removed. An irrigation system was used to apply low, intermediate, and high levels of water and produce three levels of biomass. Grown over three years, switchgrass increased carbon in the soil under each watering level, but the greatest effect was in the high watering regime where this crop was most productive. Release of CO2 during decay of crop litter by microbes depended upon switchgrass productivity, with greatest CO2 production in the high water level. Microbial breakdown of organic N and C under switchgrass was greater than under a conventional wheat crop. Introduction of switchgrass initiates major changes in the soil through organic matter input.

Technical Abstract: Switchgrass and other perennial grasses have been promoted as biomass crops for production of renewable fuels. The objective of this study was to evaluate the effect of biomass removal on soil biogeochemical processes. A three year field study consisting of three levels of net primary productivity (low, intermediate, and high growing season precipitation) and two biomass crops (winter wheat and switchgrass) was conducted near Pendleton, OR. Switchgrass increased soil C:N ratio, but the effect varied with net primary productivity (NPP) and soil depth. In-situ soil respiration (CO2) rate from switchgrass increased with NPP level, but switchgrass had higher cumulative flux than wheat in medium and low NPP. Nitrogen mineralization rate under switchgrass was significantly higher than wheat at high and medium NPP and the same trend was observed in the case of microbial biomass carbon. Introduction of switchgrass initiates major changes in soil nutrient dynamics through organic matter input.