Sustainable Intercropping of Switchgrass and Hybrid Poplar for Bioenergy Production

Emi Kimura

Switchgrass (Panicum virgatum L.) is a perennial warm-season grass that has been selected as an important lignocellulosic feedstock to support bioenergy production. Intercropping of two perennial species, switchgrass and hybrid poplar (Populus spp), will maximize the benefits of perennial cropping system through improving land and water use efficiency, soil N cycles, and diversifying the ecosystem. However, establishment of switchgrass is hindered by the dormant seeds that produce weak seedlings in the fields. Limited information is available on switchgrass biomass production and forage quality in west of the Rocky Mountains under irrigation. The objectives of our study were to; (1) determine the influence of freeze-thaw treatment on the seed dormancy; (2) quantify the effect of freezing storage at -20°C or at -80°C for five storage lengths to enhance seedling vigor of seven seed lots of switchgrass; (3) determine the influence of hybrid poplar on switchgrass biomass, architecture, and land use efficiency of the two perennial species under irrigation; and (4) determine the influence of intercropping switchgrass with hybrid poplar on the forage quality of three switchgrass cultivars over multiple growing seasons. No freeze-thaw treatments were effective on breaking seed dormancy of all seed lots used in this study. The extreme temperatures may have increased seed damage possibly by damaging the seed coat. Seed storage at freezing temperatures enhanced seedling vigor through increasing germination percentage, seedling emergence speed, and total shoot and root DM regardless of storage length up to eight months of freezing storage. Switchgrass yield decreased each year under both cropping systems due to the water stress from excessive irrigation water that was supplied to maximize hybrid poplar growth. Despite the yield loss, land use efficiency of intercropping was maintained at LER 1.7. Significant quality differences developed after second production year due to slow growth rate under intercropping compared to monoculture cropping. Forage quality by plant component revealed that the influence of intercropping was different on leaves and stems. This work provides an understanding of switchgrass seed dormancy and effects of intercropping on biomass production and forage quality in the Pacific Northwest under irrigation.

Sustainable Intercropping of Switchgrass and Hybrid Poplar for Bioenergy Production

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