Impact of Biomass Production Strategies On Nitrate-Nitrogen Concentrations and Fluxes In Iowa.

Nitrate-nitrogen export from row-crop systems throughout much of the U.S. cornbelt is a concern for local water quality and Gulf of Mexico Hypoxia.  As dedicated bioenergy crops are pursued there is a need to investigate the impacts of these production systems on nitrate-nitrogen concentrations and fluxes.  Three studies in central Iowa are specifically examining this need through monitoring of nitrate-nitrogen in subsurface drainage or soil water within the plant root zone.  The studies are comparing various perennial or annual-based biomass production strategies to a corn-soybean or continuous corn system for grain production.  The perennial based systems include diverse prairie, monoculture switchgrass, and a tree-based system.  Annual-based systems include continuous corn with and without a winter rye cover crop and stover removal, triticale/sorghum with biomass removal for both, and a corn-soybean-triticale/soybean rotation with biomass removal for corn and triticale. Early results indicate dramatic reductions in nitrate-nitrogen concentrations within or leaving the root-zone when perennial-based systems are used even when these perennial systems are fertilized with nitrogen fertilizer.  Also, annual systems that include more year-round cover (e.g. with a cover crops or triticale/sorghum system) have been found to have reduced nitrate-nitrogen concentrations.  At locations where the flux of nitrate-nitrogen has been monitored from subsurface drainage dramatic reductions have been observed.  These results indicate the potential that perennial-based biomass production systems have for reducing nitrate export to downstream waterbodies.