Evaluating Switchgrass (<i>Panicum virgatum</i> L.) as a Feedstock for Methane Production in Northern Europe
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Interest in using warm-season grasses, including switchgrass (SG) (Panicum virgatum L.), as a bioenergy crop has increased in Europe. This study evaluated the effects of harvesting regimes with two cuts per year on productivity, chemical composition and methane potential of SG cultivars ‘Dacotah’, ‘Foresburg’ and ‘Cave in Rock’in environments with cool and moderate climates in Europe with minimal fertilizer application. The results of two harvest years suggest that biomass yield, chemical composition and energy potential depend on grass cultivars and harvesting time. Significant effects (P<0.05) of harvest date and cultivar were observed for most measured parameters for biomass and silage quality. All three SG cultivars harvested on August 8 produced the lowest (P<0.05) volume of methane per kg of biomass (181–202 normal litres (NL) per kg-1 volatile solids (VS) compared to biomass of the respective cultivar harvested on July 14 (287–308 NL kg-1 VS) or on October 3 as regrowth after the first cut made in mid-July (274–307 NL kg-1 VS). Stands of all three SG cultivars, when the first harvest was done in mid-July, achieved a higher annual area-specific methane yield than those harvested first in August (1128–1900 Nm3 ha-1 and 888–1332 Nm3 ha-1, respectively). Depending on the harvest regime and cultivar, annual gross energy presented as lower heating value varied from 31.8 GJ ha-1 to 68.0 GJ ha-1. It is concluded that SG growing under the cool temperate climate of Northern Europe could be an interesting alternative crop for methane production. Our study proved that cultivar choice also plays an important role.