Quantifying Ecohydrologic Impacts of Perennial Rhizomatous Grasses On Tile Discharge, a Plot Level Comparison of Continuous Corn, Mixed Prairie, Upland Switchgrass, and Miscanthus x Giganteus.

Comparative analyses of candidate second generation biomass species are needed to understand the hydrologic, agronomic, and environmental impacts of species deployment for biomass production.   Our objective was to quantify tile drain event volume, nitrate concentrations and load for upland switchgrass (c.v. Shawnee), Miscanthus x giganteus, and big bluestem (Andropogon gerardii) dominant mixed prairie, as well as tilled continuous maize (Zea mays L.) control.   Plants were grown in large, in-ground lysimeters at the Purdue University Water Quality Field Station near West Lafayette, IN on soils characterized predominantly as Drummer silty clay loam.  Hourly drain flow was collected from 1995 to 2011 using tipping buckets fed by the 265 m² clay-lined lysimeters each draining a 0.1 m wide tile buried at a depth of 0.9m.  Nitrate concentration samples were collected as a mixed composite of tips accumulated every 24 to 72 hours during storm events from 1998-2011.  A paired regression analysis was used to mitigate environmental and climatic impacts on inter-tile variability to quantify shifts in total event flow.  Miscanthus-transitioned tile mean event flow decreased significantly at p<0.20, while switchgrass-transitioned tile response varied across replicates, including significant decreases (p<0.10) and significant increases (p<0.05) in mean event flow.  Average nitrate concentration decreased significantly in response to switchgrass and Miscanthus cropping system transitions.  Nitrate concentrations were significantly lower in Miscanthus-transitioned tiles compared to switchgrass and mixed prairie system tiles once plants were established.  Cumulative event nitrate loads were also significantly lower for all perennial plots compared to continuous maize control.  Results suggest that although transition into switchgrass and Miscanthus predominantly decreases total event flow, increases in tile drain event flow may be observed due to site-specific conditions including preferential flow.  Perennial crops improved tile nitrate concentrations significantly, which resulted in significantly lower net load from perennial system tile drains.