Switchgrass is a perennial grass with a C₄ photosynthetic pathway. It is sown from seed and forms clumped growth above ground and gradually spreading rhizomes below ground. It is distributed across North, Central and South America and in parts of Africa. The stiff erect stems grow to 0.5 – 2.5 m in height. There are two main ecotypes, the lowland tall type with coarse leaves and the upland slower growing type with finer leaves but varieties exist suited to a range of climatic conditions.

Agronomy

Seeds are sown using a small seed drill in spring into a well prepared seed bed (ploughed and harrowed) at a depth of 1cm when soil temperature has reached 10-15°C. Plant density can be up to 400 plants per m², but in the UK a seed rate of 10kg / ha produced a range of between 189-301 plants per m2 (Christian, 1994). Plants will tolerate acid conditions but additions of lime to achieve a neutral soil pH will produce best establishment and growth. Fresh seed can have a high % of dormancy, thus to achieve a high germination rate year old seed are often used.

Switchgrass is highly frost tolerant, however, is not competitive during the first year and therefore requires the elimination of weed species (Vogel, 1995). Phosphorus and potassium may be added to deficient soils to encourage seedling development, but nitrogen additions to a new crop early in spring will encourage weed coverage at a time when the crop is particularly susceptible to competition. Treatment with pre-emergent herbicide is recommended, particularly to combat broadleaved weeds. Switchgrass has a low nutrient demand, as nutrients are transported to, and conserved within, the rhizome before harvest. It displays efficient water-use so can tolerate periods of dryness. Once established, switchgrass demonstrates a good resilience to pest and disease.

Under good weed control, shoots emerge in late spring and senescence starts with falling autumn temperatures. Crops can be harvested during winter. Crops are harvested with a standard mower conditioner and are baled to required sizes. Moisture content at baling is variable at between 15-30% which is low enough to allow the crop to be stored without a period of drying. The average yield for the three best varieties in the UK at the end of a four year growing period was 11t/ha dry matter per year but yields have reached up to 18 odt/ha in south-east England (Bullard et al., 2004). Switchgrass has a productive lifespan of 10-15 years. In the USA, Parrish et al. (1993) demonstrated that 50 kg/ha Nitrogen additions produced optimal results. Nutrient content at harvest is very low for switchgrass which is beneficial to combustion efficiency and emission levels. The crop is capable of producing an energy content of 18.4 MJ/kg.

Switchgrass is currently not considered a front-runner in the search for viable and productive biomass crops in the UK. The main reason for this is the required intensity of weed management needed in the establishment phase of the crop. On a commercial scale this level of unreliability makes switchgrass a high risk crop. However, familiarity with the crop may develop to such a stage that low establishment costs, high yields and standard management techniques make it an attractive proposition. Alternative uses for switchgrass include fodder, bedding, paper fibre, composite manufacture and ethanol production (280 litres per tonne of dry matter).

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Bullard et al (2004) Identifying the yield potential of Miscanthus x giganteus: an assessment of the spatial and temporal variability of M. x giganteus biomass productivity across England and Wales. Biomass and Bioenergy 26 (1): 3-13

Christian, D.G. (1994) Quantifying the yield of perennial grasses grown as a biofuel for energy generation. Renewable Energy 5(2): 762-766.

Moser, L.E. & Vogel, K.P. (1995) Switchgrass, Big Bluestem and Indiangrass. In: Barnes, R.F., Miller, D.A. and Nelson, C.J. (eds) An introduction to grassland agriculture. Forages, 5th edn, vol.1, Iowa State University Press, Ames, pp.409-420.

Parrish, D.J., Wolf, D.D. and Lee Daniels, W. (1993) Perennial species for optimum production of herbaceous biomass in the Piedmont. Management study, 1987-1991, ORNL/Sub/85-27413/7. National Technical Information Service, US Departmrnt of Commerce, Springfield, USA.