Post-Senescence Composition and Yield of Two Switchgrass Cultivars Receiving Three Nitrogen Rates.

Post-senescence composition and yield of switchgrass (Panicum virgatum L.) are important to determine its value as a biofuel. ‘Liberty’, a lowland x upland cultivar bred for increased biomass, and ‘Shawnee’ an upland cultivar developed for increased digestibility were evaluated in field studies. Plots were located near Roann and Trafalgar, Indiana. Cultivars received three nitrogen rates, 0, 67, and 134 kg ha-1, and were sampled on September 21 (Trafalgar) and September 27 (Roann) in 2016. Compositional analysis was completed using NIRS and known calibration equations. Acid Detergent Fiber (ADF) and Neutral Detergent Fiber (NDF) did not differ between locations within a cultivar. ADF and NDF were significantly higher in Liberty as compared to Shawnee across all nitrogen rates. On average, ADF and NDF values were 25 and 30 mg kg-1 higher, respectively, in Liberty than Shawnee. There were no significant differences in Acid Detergent Lignin (ADL) between Shawnee and Liberty; however, ADL was significantly different with increasing nitrogen rates for each cultivar. ADL ranged from 79 (0 kg N ha-1) to 85 mg kg-1 (134 kg N ha-1). Nitrogen concentration was not significantly different between cultivars. Increasing nitrogen rates resulted in higher nitrogen concentration. Values ranged from 1.6 (0 kg N ha-1) to 3.9 mg kg-1 (134 kg N ha-1). Digestibility of Shawnee was 38 mg kg-1 higher than Liberty. When harvested in November, Liberty and Shawnee yielded 7730 and 6270 kg ha-1, respectively. Overall, increased yield and fiber in Liberty demonstrates that cultivar development is an important contribution to the future use of switchgrass as a biofuel feedstock.