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There is a growing demand for diverse biofuels in the United States. Potential feedstocks for cellulosic ethanol include corn (Zea mays, L.) stover and switchgrass (Panicum virgatum, L). Lands used to provide for corn production can provide some cellulosic feedstock through corn stover, but crop residue removal can have negative impacts on soil quality. Furthermore, arable land must supply both fuel and food. To meet both demands, lands considered marginal for row-crop production will likely be used to produce dedicated bioenergy crops such as switchgrass. Marginal lands are typically placed in conservation programs because they are prone to erosion and soil quality degradation, so it is imperative to understand the impacts biofuel production have on marginal soils. A long term, no-till, marginal site in eastern Nebraska was established to assess the impacts of management on soil quality. This study considers continuous corn, switchgrass, and soybean (Glycine max (L.) Merr.) as an interim crop, as well as nitrogen (N) and harvest practices in corn (residue retention/removal) and switchgrass plots (harvest in August or October). Soil microbial data, nitrous oxide (N2O) emissions, crop N use efficiency, and soil N were measured to assess management impacts on soil, water, and air quality at this site. Abundances of soil microbial biomarkers and biomass responded to all treatments, but crop type was the strongest determining factor. In one of two years of observation, there was no significant treatment effect on N2O emissions. In the second year, N2O emissions increased with N fertilization. Crop N recovery varied with all treatments and year. Relatively low levels of soil nitrate (NO3-) were found under switchgrass and soybean plots, compared to higher levels under corn plots. Switchgrass production on marginal soils appears less likely to result in N loss as N2O or NO3- than corn. High microbial biomass, soil organic matter and low NO3- concentrations also suggest soil quality will be better retained under switchgrass than corn.
Advisers: Daniel Snow, Virginia Jin