Miscanthus Grass

Miscanthus x giganteus is a giant grass similar to sugar cane. It grows up to 4 metres tall and is showing promise for a variety of primary industry applications. The possible uses for this long-lasting perennial from Japan range from shelterbelts that work with central pivot irrigators; a biomass source for renewable fuel; an effective mulch for horticulturalists; and a plant for absorbing nitrogen to reduce leaching into ground water.

Miscanthus is a ‘C4 grass’ which means that its photosynthesis is much more efficient than normal plants. Its rapid growth means the plant absorbs large amounts of nitrogen from the soil, prohibiting excess nitrogen from leaching into ground water.

It has been grown and used in Europe as a commercial energy crop since the early 1980s. It is used for combustion in furnaces (predominantly co-firing in traditional coal powered furnaces) and is a biomass source for conversion into biofuel. Global research shows Miscanthus x giganteus grown in Europe could supply 12% of the EU's energy need by 2050.

Professor Steve Wratten at Lincoln University has been involved in a variety of research around the myriad of possibilities for Miscanthus x giganteus in New Zealand. With a drive for more sustainable fuels and commitments (like that of Air NZ to using biofuel blends in the near future) the initial research focused on the grass as a source of energy.

With funding from Westland Milk Products Ltd, Steve Wratten initially looked at Miscanthus as shelter and biomass for alternative fuels here in New Zealand. The low mineral, moisture and ash content make it an attractive choice as a biofuel and unlike first generation biofuels produced from canola, the hardy grass does not require or have to take up premium food growing land. The grass is tolerant to a variety of conditions from high winds, light frosts and soil temperatures down to -3°C to drought conditions. It also grows on poor soils and is low maintenance, with no significant issues with disease or pests and no trimming or fertilizer requirements (beyond some nitrogen when the seedlings are young).

The grass is traditionally harvested for fuel in late winter from the second year of growth onwards. It can yield up to 40 tonnes of dry matter per hectare. This could produce about 9,000 litres of renewable diesel at $1.17 per litre.

In order to convert the dry matter to biofuel on a commercial scale requires specialist equipment that is not yet in New Zealand. Some Miscanthus fuel is being shipped to New Zealand in order for analysis work to be done to show that the fuel has a lower sulphur and higher cetane than mineral diesel – making it a more attractive option.

Unlike other biomass crops, Miscanthus does not require large plants for conversion.

Harvesting is usually done with a maize/forage harvester. Farmer Mark Williams, who was involved in the shelterbelt research, said they harvested some with standard haymaking equipment but the grass was “pretty tough on the gear”.

Steve Wratten has a vision for smaller collective producers – for example a group of farmers could collectively own a plant and share the initial capital outlay. They could then grow a crop for their own use with a percentage of fuel in proportion to the dry matter they contributed. Wratten says there are opportunities to build mobile units for smaller-scale processing on farms to supply directly to farm fuel tanks or sell. Alternatively, a plant could be set up as a mobile operation.

Another fuel use is in furnaces used by industries such as pulp and paper mills, dairy factories, meat processors and coal fired power stations. The dry matter can be readily processed to the requirements of existing or new boilers and co-fired (in proportions up to 50% or more) with coal without major boiler modifications.

Creating pellets for pellet burners also offers potential locally and for export.

Fonterra investigated dried Miscanthus as a fuel for its milk drying plants but it proved too light for compatibility with its coal-fired furnaces. Further work is needed to look at the use of dried pellets for fuelling furnaces.

Fonterra also have a 2ha trial plot at their Darfield plant to take advantage of the ability of Miscanthus to take up nutrients. It has reportedly had a dramatic effect on the reduction of nitrogen leaching from factory effluent.

Wratten, along with Miscanthus NZ Ltd, is looking at other uses too. An early project looked at the grass as a multi-functional tool for dairy farmers on the Canterbury plains. PhD student Chris Littlejohn worked with Canterbury dairy farmer Mark Williams with funding from Westland Milk Products and DairyNZ to trial the grass as a shelterbelt.

In 2013 trial belts 6 metres wide were planted along paddock margins on Mark’s farm (although it is anticipated that end belts will be around 3 metres wide). Researchers were particularly interested in Canterbury farms in order to quickly replace shelterbelts that have been removed to allow the operation of large centre pivot irrigators.

Centre pivots can operate easily by pushing over the grass and the grass flicks back up without snapping (unlike related bamboos).

The grass grows fast – up to 4 metres within 3 to 4 years and it does not compete with adjacent pasture. Data shows that it actually increases pasture growth by 14%.

Additional research by Morgan Shields shows the grass improves biodiversity – providing a habitat for native skinks and encouraging bumblebees and, unlike flaxes and toi toi, it does not encourage rodents.

Biodiversity benefits in regards to pollinators and lack of competition with pasture or crops suggest Miscanthus has considerable potential value for horticulture.

There is also research underway with Miscanthus as mulch in orchards. Early evidence is showing it to be excellent at retaining moisture and an attractive habitat for native earthworms.

Dry Miscanthus is absorbent and can be used as bedding for calves, poultry or sheep – and in turn producing a nutrient-dense mulch for recycling.

Miscanthus is a sterile hybrid so it can't reproduce itself by seed and spreads only slowly by creeping rhizomes (about 10cm a year). The rhizomes that develop after two years can be split for new plants.