16 June 1995

Bags of choice for energy

GROWERS seeking low input biomass crops for energy could soon be spoiled for choice. Besides willow, poplar and several types of miscanthus, or elephant grass, Rothamsted researchers are examining rye and several perennial grasses from warmer climates and/or adapted to low grade soils.

Among them are Spartina (cord grass), Phalaris (reed canary-grass), and seven varieties of Panicum (switchgrass) from the American prairies. The last two species can be grown from seed, which could be a big advantage, says Dudley Christian. Miscanthus, a sterile hybrid, must be propagated by planting rhizomes, he explains. "So its very expensive to establish."

One tonne of biomass dry matter contains roughly the same energy as 0.5t of coal, says Mr Christian. The coal emits 400kg of the greenhouse gas carbon dioxide when burned. But the CO2 released from the biomass is only that absorbed by the plant during growth. "Its a valuable environmental bonus."

After only a years trial it is too soon to say if the dry matter yields are sustainable, says Mr Christian. But with just 60kg/ha (48 units/acre) of nitrogen miscanthus has given up to 8t/ha (3.2t/acre) of dry matter. Switchgrass has given similar yields, but Phalaris managed as much as 20t/ha (8t/acre) in two cuts over a 12-month period, he notes. "We believe some of these other crops may be as good as willow."

Phalaris, for example, could become a useful "dual-purpose" crop, he suggests. It grows well at low temperatures and is used for forage in Canada and New Zealand. That offers the prospect of taking an early bite in, say, March and then growing it on for fuel, sharing the costs between two enterprises.

In Sweden, Phalaris fibres are used for making high quality paper. The waste is then powdered and used as a fuel in oil burners with little modification, says Mr Christian.

Rye as an annual has given up to 17t/ha (6.8t/acre) of dry matter – about half as grain. "If rye looks good we could go back to the breeders and see if they could introduce genes for less grain and more straw." This would reduce the need for post-harvest drying, he explains. Rye is known to do well on poor soils.

Panicum looks particularly useful with its range of maturity dates – some varieties being fit to cut in October, others as late as February.

"They all came off at roughly the same moisture – about 36%." The wider harvest window than for miscanthus could reduce storage needs, he explains. &#42