Switchgrass Biomass Quality as Affected by Nitrogen Rate, Harvest Time, and Storage

Abstract

Core Ideas Switchgrass, being an efficient perennial biofuel crop, can be used as an alternative to fossil fuels and help in the sustainability of energy. Thus, it is important that we understand the effect of storing switchgrass for extended periods of time. Storing switchgrass for an extended period may have an impact on quality and yield. Storing switchgrass in bales or as a standing crop in the field are two storage methods assessed in this study. The purpose of this study was to assess the changes in switchgrass (Panicum virgatum L.) biomass quality as affected by N rate, harvest time, and storage. This research was conducted near Bristol, SD, in 2010 and 2011. Treatments included three N rates (0, 56, and 112 kg N ha−1) applied annually and each N rate replicated four times. After a killing frost, all of the plots were harvested and baled in large round bales in October 2010 and November 2011. An area of about 30 m2 from each plot was left unharvested to represent storage of standing switchgrass over the winter and to determine dry matter yields. Switchgrass was analyzed for hemicellulose, cellulose, lignin, mineral elements, N, and C. In the first season, storage of the fall harvested switchgrass bales numerically increased the concentrations of hemicellulose, lignin, and N. In the second season, they increased significantly. Mineral elements significantly increased in both sampling seasons. Delaying harvest until spring decreased lignin, N, and mineral elements concentration, and increased cellulose and hemicellulose concentrations, but also reduced biomass yield. Results from this study suggest that delaying the switchgrass harvest until spring increased the overall feedstock quality for ethanol production, but yield reductions must be considered to determine the overall economic impact of a delayed harvest.