The Impact of Switchgrass Cultivar Diversity on Nitrogen Use Efficiency

Abstract:

The search for new sources of sustainable energy has cast attention on switchgrass (Panicum virgatum L.) as a potential biofuel crop. However, growing switchgrass in a high-input, low-diversity cropping system can have negative environmental consequences, such as enhanced nitrate (NO₃) leaching and nitrous oxide (N₂O) emissions. Increasing plant diversity has been shown to promote plant production by increasing nitrogen (N) use efficiency (NUE), which may lower fertilizer requirements in cropping systems. With this study we asked how increasing cultivar diversity of switchgrass impacts NUE. The study took place at Fermilab National Environmental Research Park in Batavia, IL. In 2013, we applied a ¹⁵N tracer label to switchgrass planted in monocultures and mixtures of 2-types, 4-types, and 6-types of cultivars. We harvested the aboveground biomass and collected soil cores after one growing season. Preliminary data showed that cultivars differed significantly in yield and in the total ¹⁵N content in aboveground biomass, but there are no differences in tissue ¹⁵N concentration. In addition, there appears to be no effect of diversity level on ¹⁵N contents or concentrations. We intend to use this aboveground and soil ¹⁵N data to calculate NUE. These results could suggest that choosing the cultivar that most efficiently takes up N and produces the most yield may be more important than increasing diversity to promote the efficacy of biofuel feedstock production. However, increasing diversity can have other positive ecological consequences and does not appear to have negative impacts on yield or the N cycle.