Switchgrass and Miscanthus long-term yield across Michigan and Wisconsin

Perennial grasses like switchgrass (Panicum virgatum) and miscanthus (Miscanthus × giganteus) are expected to supply a substantial amount of the United States bioeconomy’s feedstock demand. However, uncertainties around patterns of long-term yields challenge the viability of this potential. To resolve long-term yield patterns, we analyzed over 200 plantings of switchgrass and miscanthus across Michigan and Wisconsin USA measured over 5 to 15 years. During a yield-building phase, peak yields occurred within 4 – 5 years after planting, followed by a 6 – 7 year yield-decline phase in which switchgrass and miscanthus lost 30 – 47% and 14 – 40% of peak yields, respectively. Added nitrogen increased peak-yields by 10 – 20% and attenuated the yield decline by 20 – 50%. A farm-to-gate economic analysis suggests replanting switchgrass and miscanthus 5 and 9 years following their peak yields optimize profit over a 30-year time horizon. This conserved long-term yield pattern has implications for crop management, breeding programs, policy, and global bioenergy with carbon capture and storage modelling.

Methods
Switchgrass and M. × giganteus long-term Yield data for this analysis was collected from were collected from multiple long-term experiments along Michigan and Wisconsin, USA. The 12 different experimental sites were planted through 2007 – 2013 and provided a wide range of conditions experimental conditions, plot sizes, and N fertilization rates. Given the multiple planting years our long-term yield dataset included different experiment lengths; 16 plots with up to 5 years of data, 86 plots with up to 9 years of data, 60 plots with up to 10 – 12 years of data, 32 plot with up to 13 years of data, and 20 plots with up to 15 years of data at the moment of analysis.