Variety interacts with space and time to influence switchgrass quality

Efficient conversion of biomass crops to energy requires an understanding of plant quality, including cell wall and mineral composition. We compared key quality parameters of two leading switchgrass (Panicum virgatum L.) varieties, lowland ‘Kanlow’ and upland ‘Cave-in-Rock’, over two growing seasons and across five landscape positions. Through a nonmetric multidimensional scaling (NMS) analysis, wherein two ordination axes together explained most of the variation in the data (r² = 0.89), we found plant mineral composition (N and ash concentrations) was influenced more by landscape position, while plant cell wall components were affected more by year of growth. Switchgrass at the floodplain position was “dirtier,” containing greater ash concentration (110 g kg⁻¹) and N concentration (6.2 g kg⁻¹) known to contaminate biochemical and thermochemical pathways. Furthermore, variety influenced quality; for example, Kanlow had less lignin than Cavein-Rock, but all biomass had greater lignin in 2011 than in 2010. Kanlow and Cave-in-Rock contained greater concentrations of total nonstructural carbohydrates (TNC) in 2010 than in 2011 by as much as 8 and 20%. While considerable work has focused on breeding for improved quality and regional-scale environmental effects, our results indicate that variety also significantly interacts with subfield-scale environmental and interseasonal effects.