(221a) High Temperatures and Low Soil Moisture Synergistically Reduce Switchgrass Yield and Inhibitbiofuel Production from Marginal Field Sites

Marginal field sites are defined based on their unsuitability for food production, and for this reason are
considering promising locations for production of bioenergy crops, which have lower input
requirements. However, the effect of drought in some marginal sites may be more severe than in arable
cropland. This has implications for both bioenergy crop yields and downstream conversion, as we have
previously shown that severely drought-stressed switchgrass completely inhibited downstream yeast
fermentation. The objective of this project was to understand how marginal field sites with various soil
characteristics under simulated drought conditions influenced switchgrass yields, composition, and
conversion to biofuels. An experiment was designed at five marginal sites with diverse soil
characteristics, spanning a latitudinal gradient in Michigan and Wisconsin. Rainout shelters were
installed in three replicate field plots at each location to simulate drought stress. During the first year of
installation (2018), the rainout shelters reduced the rainfall by 60%, causing a statistically significant
reduction in switchgrass fermentability harvested at the Wisconsin Central - Hancock field site
compared to the ambient samples, which was not observed at the other locations. Among the five sites,
the Hancock site had a unique Entisol soil type that led to comparatively low soil moisture and high soil
temperatures during the growing season, which was exacerbated by the simulated drought. This
reduction in fermentability was not expected based on either the biomass or hydrolysate composition,
which were comparable between the control and treatment, indicating that more research is needed
before we can predict the impact of drought on biofuel production.