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.