Where's the nitrogen? The timing and impacts of internal nitrogen cycling on switchgrass (Panicum virgatum L.) yield and biofuel quality.

摘要

Research focused on dedicated bioenergy crops that can be used to meet our advanced biofuels goal, i.e., made from non-food sources like agricultural residues and lignocellulosic feedstocks, has found switchgrass (Panicum virgatum L.) to be a leading candidate species. Switchgrass requires nitrogen (N) in greater quantities, compared to other nutrients, for plant biomass production, but high N concentration ([N]) is undesirable in the harvested biomass feedstock for two reasons: (1) it is economically and environmentally expensive to replace N removed from cropping system and (2) N reduces the conversion efficiency of biomass to biofuels via thermochemical conversion. Immediate reductions in the [N] of the harvested portions of perennial feedstocks, including switchgrass, can be achieved by exploiting seasonal internal N cycling. The biology of switchgrass provides some opportunity to naturally manipulate the [N] of this biomass feedstock, but there is a trade-off between the quantity and quality of the feedstock depending on the time of harvest. The research objectives of this project were to: (1) elucidate the spatial and temporal distribution of N in above- and below-ground tissues of field-grown switchgrass to determine its impacts on yield and N removal and (2) determine how switchgrass harvest date influences biofuel quality from fast pyrolysis. We recommend harvesting post-frost switchgrass biomass for improved long-term yields and reduced [N] in the harvested portions of biomass that can result in reduced N removal. This will benefit both biomass producers and also thermochemical facilities who will receive low-N biomass to reduce conversion costs.