By Sally Brown, University of Washington

Switchgrass is a high biomass crop that is a potential feedstock for cellulosic ethanol.  It is an environmentally friendly alternative to corn based ethanol, because it is a perennial rather than an annual crop, and because all of the above ground plant tissue can be used for fuel production.  Steve Fransen from WSU is the switchgrass expert for the Northwest and he is predicting that demand for this feedstock will soon skyrocket, particularly with a cellulosic ethanol plant under construction in Boardman, OR.

The University of Washington got a $2 million grant to study ammonia oxidation mechanisms in bioenergy production- namely the role of different soil organisms in oxidizing ammonia and any associated differences in N2O release.  While N2O emissions are typically associated with denitrification, there are also emissions associated with this stage of the nitrogen cycle.  Previously it had been thought that two types of bacteria were the only soil microbes that were able to oxidize ammonia in a two step reaction.  Recently it has been discovered that archaea, a primitive family of single celled organisms that are critical in anaerobic digestion systems, can also mediate this reaction.  With some additional funding from NBMA and King County, biosolids treatments were integrated into the field design at one of the study sites.  As an agronomic crop with a high nitrogen demand, switchgrass has the potential to be an end use crop for Class B biosolids.

Biosolids were added at 4 and 8 dry tons per acre to a field site in Paterson, WA.  Dried material we used in the study was provided by Natural Selection Farms.  The low and high biosolids were paired with high and low rates of synthetic fertilizers.  We just finished applying biosolids and fertilizers for the 2nd growing season.  Yield results from the two first season harvests are forthcoming.  Initial results from the field gas measures are shown in the graph above.  Although N2O emissions were generally low, they were slightly increased in the high biosolids treatment in comparison to the control.  Initial results are also suggesting that the biosolids soils have different microbial populations in terms of relative abundance of different communities of archaea and bacteria.  Additional results will be shown at this year’s Biofest poster session.