Miscanthus × giganteus
Miscanthus × giganteus, also known as the giant miscanthus, is a sterile hybrid of Miscanthus sinensis and Miscanthus sacchariflorus. It is a perennial grass with bamboo-like stems that can grow to heights of 3– in one season. Just like Pennisetum purpureum, Arundo donax and Saccharum ravennae, it is also called elephant grass.
Miscanthus × giganteus' perennial nature, its ability to grow on marginal land, its water efficiency, non-invasiveness, low fertilizer needs, significant carbon sequestration and high yield have sparked significant interest among researchers, with some arguing that it has "ideal" energy crop properties. Some argue that it can provide negative emissions, while others highlight its water cleaning and soil enhancing qualities. There are practical and economic challenges related to its use in the existing, fossil based combustion infrastructure, however. Torrefaction and other fuel upgrading techniques are being explored as countermeasures to this problem.
Use areas
Miscanthus × giganteus is mainly used as raw material for solid biofuels. It can be burned directly, or processed further into pellets or briquettes. It can also be used as raw material for liquid biofuels or biogas.Alternatively, it is also possible to use miscanthus as a building material, and as insulation. Materials produced from miscanthus include fiberboards, composite miscanthus/wood particleboards, and blocks. It can be used as raw material for pulp and fibers as well as molded products such as eco-friendly disposable plates, cups, cartons, etc. The pulp can be processed further into methylcellulose and used as a food additive and in many industrial applications. Miscanthus fiber provides raw material for reinforcement of biocomposite or synthetic materials. In agriculture, miscanthus straw is used in soil mulching to retain soil moisture, inhibit weed growth, and prevent erosion. Further, miscanthus' high carbon to nitrogen ratio makes it inhospitable to many microbes, creating a clean bedding for poultry, cattle, pigs, horses, and companion animals. Miscanthus used as horse bedding can be combined with making organic fertilizer. Miscanthus can also be used as a fiber source in pet food.
Life circle
Propagation
Miscanthus × giganteus is propagated by cutting the rhizomes into small pieces, and then re-planting those pieces below ground. of miscanthus rhizomes, cut into pieces, can be used to plant 10–30 hectares of new miscanthus fields. Rhizome propagation is a labor-intensive way of planting new crops, but only happens once during a crop's lifetime. Alternative propagation techniques are available, or in development such as nodal propagation. For seed based propagation, a halving of the cost is predicted.Management
The plant requires little if any herbicide, and only at the beginning of its first two seasons. Afterwards the dense canopy and the mulch formed by dead leaves effectively reduces weed growth. Because of miscanthus' high nitrogen use efficiency, fertilizer is also usually not needed. Mulch film, on the other hand, helps both M. x giganteus and various seed based hybrids to grow faster and taller, with a larger number of stems per plant, effectively reducing the establishment phase from three years to two. The reason seems to be that this plastic film keeps the humidity in the topsoil and increases the temperature.Yield
Miscanthus is unusually efficient at turning solar radiation into biomass, and its water use efficiency is among the highest of any crop. It has twice the water use efficiency of its fellow C4 plant maize, twice the efficiency as the C3 energy crop willow, and four times the efficiency as the C3 plant wheat. The typical UK winter harvest of 11–14 tonnes dry mass per hectare produce of energy per year. This compares favorably to maize, oil seed rape, and wheat/sugar beet. In the USA, M. × giganteus has been shown to yield two times more than switchgrass.In many locations in Europe, miscanthus plantations produce more net energy than any competing energy crop, because of high yields and low demands for farm management energy use. The main competitors yieldwise is willow and poplar, grown at short rotation coppice or short rotation forestry plantations. In the northern parts of Europe, willow and poplar approach and sometimes exceed miscanthus winter yields in the same location. Globally, FAO estimates that forest plantation yields range from dry mass per year. Russian pine have the lowest yield, while eucalyptus in Argentina, Brazil, Chile and Uruguay, and poplar in France/Italy, have the highest, with 7.8–12.2 t/ha for eucalyptus and 2.7–8.4 t/ha for poplar. IPCC estimates that global plantation forest yields varies between 0.4 and 25 tonnes, with most plantations producing between 5 and 15 tonnes. Natural forests have lower yields however, between 0.1 and 9.3 dry tonnes per hectare per year, with most natural forests producing between 1 and 4 tonnes. The average yield for natural forests in temperate climates is 1.5 to 2 dry tonnes per hectare per year before harvest related losses.
The miscanthus peak yield is reached at the end of summer but harvest is typically delayed until winter or early spring. Yield is roughly one third lower at this point because of leaves drop, but the combustion quality is higher. Delayed harvest also allows nitrogen to move back into the rhizome for use by the plant in the following growing season.
In Europe the peak dry mass yield has been measured to roughly, depending on location, with a mean peak dry mass yield of 22 tonnes. Individual trials show peak yields of 17 tonnes, 17–30 tonnes, 25 tonnes, 39 tonnes, and 42–49 tonnes. Individual trials also show delayed yields of 10 tonnes, 11–17 tonnes, 14 tonnes, 10–20 tonnes, 16–17 tonnes, 22 tonnes, 20–25 tonnes, 26–30 tonnes and 30 tonnes. A different trial showed delayed yields of 15 tonnes in Germany. Researchers have estimated a mean delayed yield of both 10 tonnes for the UK, and between 10.5 and 15 tonnes for the UK.
As can be seen, yields are highest in southern Europe; in general 25–30 tonnes under rainfed conditions. With irrigation, individual trials in Portugal yielded 36 tonnes, Italy 34–38 tonnes, and Greece 38–44 tonnes. Trials in Illinois, USA, yielded. Like in Europe, yields increase as you move south.
For biomass in general, yields are expected to be higher in tropical climates than in temperate climates. For Miscanthus × giganteus specifically, researchers disagree about the yield potential however. Since there are no actual field trials done in the tropics yet, only estimates based on theory is possible. Some argue that the plant tolerates heat, and that the yield potential is between 60 and 100 dry tonnes per hectare per year. Others argue that heat tolerance is low, and subsequently predict low yields. There is agreement that other miscanthus genotypes have a high tolerance for heat, e.g. Miscanthus Sinensis. Other elephant grass types clearly suited to high temperatures have been shown to yield up to 80 tonnes per hectare, and commercial napier grass developers advertise yields of roughly 100 dry tonnes per hectare per year, provided there is an adequate amount of rain or irrigation available.
In general, yield expectations are lower for marginal land than for arable land in the same geographical area. Marginal land is land with issues that limits growth, for instance low water and nutrient storage capacity, high salinity, toxic elements, poor texture, shallow soil depth, poor drainage, low fertility, or steep terrain. Depending on how the term is defined, between 1.1 and 6.7 billion hectares of marginal land exists in the world. For comparison, Europe consists of roughly 1 billion hectares, and Asia 4.5 billion hectares. According to IRENA, 1.5 billion hectares of land is currently used for food production globally, while " about 1.4 billion ha additional land is suitable but unused to date and thus could be allocated for bioenergy supply in the future." The IPCC estimates that there is between 0.32 and 1.4 billion hectares of marginal land suitable for bioenergy in the world. The EU project MAGIC estimates that there is 45 million hectares of marginal land suitable for Miscanthus × giganteus plantations in the European Union, with three classes of expected yield.
Miscanthus × giganteus is either moderately or highly tolerant of heat, drought, flooding, salinity, and cool soil temperatures. This robustness makes it possible to establish relatively high-yielding miscanthus fields on marginal land, for instance in coastal areas, damp habitats, grasslands, abandoned milling sites, forest edges, streamsides, foothills and mountain slopes. 99% of Europe's saline, marginal lands can be used for M. × giganteus plantations, with only an expected maximum yield loss of 11%. Since salinity up to 200 mM does not affect roots and rhizomes, carbon sequestration carry on unaffected. Researchers found a yield loss of 36% on a marginal site limited by low temperatures, compared to maximum yield on arable land in central Europe. They also found a yield loss of 21% on a marginal site limited by drought, compared to maximum yields on arable soil in central Europe.
Researchers predict an average yield of 14.6 dry tonnes per hectare per year for miscanthus on marginal land in China, 12.6% below expected average yield on arable land. They calculate that miscanthus on marginal land in China can produce 31.7 EJ of energy annually, an amount equivalent to 39% of the country's 2019 coal consumption. An individual trial in Ireland showed an average delayed yield of 9 tonnes per hectare per year on a site troubled by low temperatures, waterlogging during winter, and dried out, cracked soil during summer. Researchers reported yields ranging from 17 to 31 tonnes on a variety of soils in the USA, and compared those to a specific trial with lightly fertilised 3 year old miscanthus crops on eroded claypan soils, common in the Midwest The miscanthus crops yielded 20–24 tonnes per hectare per year. The authors concluded that " eroded claypan soils may not negatively impact Miscanthus establishment or yield."
Yield prediction software Miscanfor predicts that 30 days of soil dryness is the mean maximum amount of time a miscanthus crop can endure before wilting, while 60 days is the maximum before its rhizomes are killed and the crop has to be replanted. In addition to adequate rainfall, soil water holding capacity is important for high yields, especially in dry periods. In soils with poor water holding capacity, irrigation in the establishment season is important because it allows the roots to reach far deeper underground, thereby increasing the plants' ability to collect water.
Miscanthus grows relatively well in soils contaminated by metals, or by industrial activities in general. For instance, in one trial, it was found that M. × giganteus absorbed 52% of the lead content and 19% of the arsenic content in the soil after three months. The absorption stabilizes the pollutants so they don't travel into the air, into ground water, neighbouring surface waters, or neighbouring areas used for food production. If contaminated miscanthus is used as fuel, the combustion site need to install the appropriate equipment to handle this situation. On the whole though, " Miscanthus is suitable crop for combining biomass production and ecological restoration of contaminated and marginal land." Researchers argue that because of miscanthus' ability to be " productive on lower grade agricultural land, including heavy metal contaminated and saline soils " it can " contribute to the sustainable intensification of agriculture, allowing farmers to diversify and provide biomass for an expanding market without compromising food security."