Aboveground Biomass Production and Water Use Efficiency During a Shift to Biofuels Production.

Concerns about the continued use of fossil fuel have made it critical to conduct research on potential biofuels from renewable sources.  The main objective of this research is to evaluate effects of the transition to biofuel production on several edaphic parameters including C and N cycles, microbial activity and C sequestration and relate them to aboveground biomass production.  Research plots were established in the semi-arid region of the Columbia Plateau in north central Oregon on a soil low at level of organic matter.  Three irrigation regimes were established to provide three levels of net primary production (NPP).  Management systems included switchgrass (Panicum virgatum), wheat (Triticum aestivum), mustard (Brassica xxx) and a polyculture consisting of four perennial grass species and two legume species.  A cooler than normal spring in 2008 reduced the expected mustard yield.  Switchgrass yield in the highest NPP was almost 15 Mg per ha, the poly culture yielded nearly 11 Mg per ha, the wheat grain yield was 9 Mg per ha while the mustard seed only yielded slightly over 1 Mg per ha.  In the first year after establishment, taking two harvests from the grass species reduced the biomass yield compared to only one harvest regardless of NPP.  Water use efficiency in the high and intermediate NPP ranged from 15 to 35 kg biomass per ha per cm of water; however, the water use efficiency in the low NPP exceeded 275 kg per ha per cm of water.  Under conditions on the Columbia Plateau the temperate grasses very effectively utilized the rather limited amount of rainfall; however, with additional irrigation a substantial amount of biomass can be produced.