Full of prairie promise
A HIGH yielding perennial grass which can be grown cheaply from seed may prove a practicable attractive energy crop alternative to short rotation coppice and miscanthus.
Switchgrass, a native of the US prairies, has been in IACR-Rothamsted trials since 1993 and shows real promise, according to researcher Dudley Christian. "The best varieties we have yield 12-14t/ha of dry matter a year. This is similar to miscanthus on the same site and is as good as short rotation willow in the UK at present."
Like miscanthus, switchgrass has the extra efficient C4 metabolism, making it particularly suitable for producing biomass, explains Mr Christian. "It has a low nutrient requirement and tolerates drought very well." So far responses to nitrogen have been low. "The need for nitrogen fertiliser is only now showing after five years of production."
The crops key advantage is that it can be drilled conventionally. Compared with miscanthus, which must currently be established by planting rhizomes or small plants, that works out much cheaper, he explains.
Commercial US switchgrass seed costs $10-15/lb. At about 10kg/ha (9lb/acre), as used in the trials, establishment comes to about £220/ha (£90/acre). "Thats quite a saving on the £800-1000/ha for short rotation coppice and miscanthus which is currently about the same."
Unlike miscanthus, the thin woody stems of switchgrass -which grows up to 1.5m (5ft) depending on species – dry well in winter to about 30% moisture. That makes the crop well suited to conventional grass harvesting methods. "I dont see why it cant be forage harvested or mowed and big baled." *
• High dry matter output.
• Low input need.
• Drought resistant.
• Established from seed.