What is Miscanthus?

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In the 35 years since the potential for Miscanthus x giganteus (MG) as a biomass crop was first recognized in Europe, interest in MG crop has grown and research has led to the development of viable systems for growing, harvesting and utilizing the crop for energy production. High biomass yield, low ash, mineral and water content, a high energy output to input ratio relative to similar biomass feedstocks, ability to withstand cold conditions and poor soils increasingly make MG the key candidate biomass fuel crop.

The energy ratio of MG has been calculated to be, at 1:32, greater than that of any other current agricultural crop, including SRC willow (1:30), wheat (1:9) and oilseed rape (1:4). One ton of MG’s biomass can replace 0.6 tons of hard coal, and 400 liters of oil, outperforming wheat straw, hemp, switchgrass and other alternatives.

CropDM yield (tDM/ha/y)Lower heating value (MJ/kg DM)Energy production per hectare (GJ/ha)Water content during harvest (%)Ash content (%)
Miscanthus18 – 3217.50300 – 56015.003.00
Straw2 – 417.0035 – 6015.008.00

Hemp

10 – 1816.80170 – 300N/AN/A
Willow8 – 1518.50280 – 31553.002.00
Poplar9 – 1618.70170 – 30049.001.50
Arundo donax13 – 3516.30245 – 57050.005.00
Phalaris arundinacea6 – 1216.30100 – 13013.004.00
Switchgrass9 – 1817.00N/A15.006.00
Acacia5 – 1019.50100 – 20035.00N/A
Wood3 – 518.70N/A50.001.00 – 1.50
  • With an average yield of about 20+ tons of dry matter from the fourth year after planting and high cellulose content (45% – 52%), MG is one of the most promising crops in the European climate.
  • Only in the planting year and the first year post-planting weed control and fertilizing are necessary. For the remaining 20+ years, this is no longer needed due to leaf fall and the rapid growth of the MG.
  • The need for fertilization is very limited (from the third year after planting 30-60kg. N/ha). This is a result of the fact MG is a C4 crop, the crop dries and the nutrients sink back to rhizomes, after leaf fall and composting of the leaves the nutrients are absorbed by the MG rhizomes.
  • Unlike some other perennial crops, MG gives no problems with removal of the crop, hybridization MG is sterile, there is no concern about invasiveness from seed.

Miscanthus x giganteus represents a key candidate energy crop for use in biomass-to-liquid fuel conversion processes and biorefineries to produce a range of liquid fuels and chemicals; it has recently attracted considerable attention. Its yield, elemental composition, carbohydrate and lignin content, and composition are of high importance to be reviewed for future biofuel production and development. Starting from Miscanthus, various pre-treatment technologies have recently been developed in the literature to break down the lignin structure, disrupt the crystalline structure of cellulose, and enhance its enzyme digestibility. These technologies included chemical, physicochemical, and biological pretreatments. Due to its significantly lower concentrations of moisture and ash, Miscanthus also represents a key candidate crop for use in biomass-to-liquid conversion processes to produce a range of liquid fuels and chemicals by thermochemical conversion. MG composition of lignin, cellulose-hemicellulose plays a crucial role in optimizing strategies for biofuels

 

Cellulose (%)

Hemicellulose (%)Lignin (%)H:L ratioAsh (%)Moisture content (%wt)
43.06 – 52.2024.83 – 33.989.27 – 12.586.20 – 8.902.16 – 3.474.10 – 4.90
*H:L ratio: hemicellulose – lignin ratio

MG’s biomass can be burned when needed – in the same way as oil, gas or coal. MG can be pressed into fuel pellets/briquettes or chipped for combustion, or it can be used as a feedstock for cellulosic biofuel production. “Energy grass” Giant Miscanthus can be used for:

  • Combustion for electricity and heat production in either biomass-dedicated plants or by being co-fired in more traditional coal plants.
  • Conversion to liquid fuels. In cellulosic fuel processes, MG is a stable and cost-effective feedstock.
  • Paper, cellulosic fiber production and fiber-based materials (sustainable pulp and packaging)
  • Construction – incorporation in the manufacture of medium density fiberboard (MDF).
  • Chemical applications like renewable plastics and additives, in place of petroleum-based ingredients.
  • Animal bedding.

The following table shows analyses results from biomass collected in Croatia:

Quality features% in dry matter% in sample
Total moisture18.80
Chlorine0.0330.027

Sulphur

0.1060.086
Ash composition% in dry matter% in sample
P2O51.831.48
Na2O0.480.39
K2O4.663.78
CaO5.774.68
MgO5.634.56
Al2O30.580.47
TiO20.020.02
Fe2O30.320.26
SiO379.3664.28
SO31.341.08
Ash melting point temperature°C
SST – shrinkage temperature1200
DT – deformation temperature1230
HT – hemisphere temperature1260
FT – flow temperature1300

As energy independence becomes a growing concern both environmentally and economically, regional communities must focus on ways to produce energy from own local natural resources. Miscanthus x giganteus (MG) can be cost-effectively converted into clean energy to help local communities meet their energy independence goals; also it can be a strong contributor to rural development. MG provides a renewable, environmentally-friendly energy source that can be locally grown and burnt. MG cultivation in rural areas can have immediate positive impacts because just one biorefinery can generate over 300 direct and indirect jobs. MG will be grown local to each facility, thereby creating jobs immediately in the areas.

The energy ratio of MG has been calculated to be, at 1:32, greater than that of any other current agricultural crop, including SRC willow (1:30), wheat (1:9) and oil seed rape (1:4). One ton of MG can replace 0.6 tons of hard coal, and 400 liters of oil, outperforming switchgrass and other alternatives. MG is a Cost-Effective Fuel, from the ground up, it just makes sense:

• Produces up to 30 harvested tons per hectare at maturity

• Up to 16 mm BTU/ton, on dry matter basis

• Moisture content at harvest of 10-15%

• Highly efficient at carbon storage 5.2-8.2 tC/ha/yr,

• Low ash content & mineral content—very clean burning

FuelkWh/tPrice/tEuro/kWhValue per GJ
Miscanthus (coppice)3.80560 €0.016 €4.36 €
*€4.36 per Giga Joule is equivalent to €0.16 cent per liter of home heating oil.

MG composition of lignin, cellulose-hemicellulose plays a crucial role in optimizing strategies for biofuels. It’s more challenging to release the sugars in this feedstock for conversion to biofuels and chemicals, but MG as a cellulosic feedstock offers several advantages over starch- and sugar- based feedstocks. MG is nonfood, it is cheaper and more abundant, so perfectly serves and provides a solution for producing more substantial amounts of biofuels and biochemicals to replace fossil fuels.

Cellulose (%)

Hemicellulose (%)Lignin (%)H:L ratioAsh (%)Moisture content (%wt)
43.06 – 52.2024.83 – 33.989.27 – 12.586.20 – 8.902.16 – 3.474.10 – 4.90
*H:L ratio: hemicellulose – lignin ratio

 

Growing MG provides many environmental benefits as well as Carbon Capture and Storage. One of the major drivers for growing MG is it potential for the reduction of Green House Gas (GHG) emissions. There are two mechanisms in which growing MG as a RES can offset carbon emissions.

Carbon mitigation:

•The energy content of MG is approximately 19 MJ kgˉ¹. One hectare produces the equivalent energy of 3,300 – 5,700 liters of light heating oil and an average medium sized house will burn around 3000 liters of oil per year, which releases 8.2 tons CO2

• MG is a carbon neutral fuel as carbon that is released during its combustion has been absorbed by the plants when they were growing.

• Greenhouse gas emissions from MG cultivation will be lower than those from other agricultural activities. This is due to lower amounts of fertilizer usage and the absence of animal related emissions.

Carbon sequestration:

• MG can store (sequester) carbon preventing its release into the atmosphere. Sequestration occurs when the inputs of carbon dioxide are greater than removals from harvesting and decomposition.

• Carbon is stored in the rhizomes and roots of MG as well as in un-harvested stubble. In addition, an increase in soil carbon will occur if MG is planted into former tillage land. Carbon captured by MG can be further enhanced if plantations are used for the bioremediation of effluents and sludge.

Besides all above MG is not a food crop like corn used for ethanol production or a forest product like conventional timber, so it does not impact food or lumber prices. MG can be grown effectively on marginal soils, mitigating the pressure for farmers & landowners to convert existing lands.

The growth pattern of the Miscanthus Giganteus (MG) crop is simple. From the underground rhizomes new shoots are produced annually. These shoots develop into erect, robust stems, which reach 0.5 – 1m in height by late August of the first year of planting, with a diameter of up to 10mm. The stems, which have an appearance similar to bamboo canes, are usually unbranched and contain spongy pith. From the third season onwards the crop can be expected to achieve a maximum height of 2.5 – 3.5m.

From late July the lower leaves senescence as canopy closure prevents sufficient light penetration. Following the first air frost in autumn senescence accelerates and nutrients move back to the rhizome. Leaves then fall and a deep leaf litter develops. Any remaining foliage dies and the stems dry to relatively low moisture content (30-50%) during winter. By March, free standing, almost leafless, canes remain and moisture content in the biomass decrease to less than 20% and it is these which are harvested mechanically. This growth cycle is repeated once spring-time temperatures increase again.

First year MG grows to approximately waist height producing 2-3 canes, year 2 it grows to approximately head height with probably 15 canes, in year 3 it grows to about 2.4-meter height with about 50 canes. MG is on a yield building phase over the first 3 years. Growth potential is dependent in temperature, sun, the water capacity within soil and the rainfall levels. Therefore sunlight and moisture are important.

Yields will vary according to age of the crop and environmental factors specific to any one particular site. The crop will take three to four years to reach a mature yield (up to five years on marginal sites). After this initial yield-building phase, MG will continue for at least 15 years. The yield from the first season’s growth, at 2-3 t/ha, is not worth harvesting; the stems do not need to be cut and so may be left in the field until the following season. However, if spring-time applications of translocated herbicides are planned then, the MG stems should be flailed in order to avoid any risk of crop uptake. From the year 2  onwards the crop is harvested annually. The second year harvestable yields may range from 8-12 t/ha, and those in the third year may achieve between 16-25 t/ha or more at 20% moisture content. Harvestable yields reach a plateau after 3-4 years. The reasons for the variation in the yield building phase duration and yield in the plateau phase depends on planting material, planting density, soil type, climate. Where moisture supply or exposure limits yield there may be a longer ‘yield-building’ phase.

Source:  Miscanthus Best Practice Guidelines

Since Miscanthus x giganteus (MG) is a sterile hybrid, the crop cannot be planted from seeds, but instead must be established with vegetative materials such as seedlings, plantlets or rhizomes (root growths – shown in Figures). Some other varieties of Miscanthus can be invasive, so it is important to choose true MG rather than other varieties. Using vigorous and healthy planting material is vital. For phytosanitary reasons, MG rhizomes should only be sourced from European or Mediterranean countries. There is currently no rhizome certification or quality standards protocol available anywhere.

MG can be adapted to various kinds of soil conditions, fields need to have well-drained soils, and the soil pH level is recommended to be in the range of 5.5-8. A soil test in the year before MG stand establishment can suggest the amount of lime that would be required to attain the recommended pH. Lime needs to be applied at least six months prior to the planting of MG.

A plant population of 13,000-15,000 plants per hectare is optimal in an established GM plantation. To achieve the target population, over-planting in the first year is recommended since 20-30% of the plants may not grow, so planting rate of 18,000 rhizomes/ha (0,75 x 075 m) is estimated to give an emergence of 13-15,000 plants/ha. This rate allows for some establishment losses while still providing the plant density required to achieve optimal yields from year three onwards and effective weed suppression through competition.

For good soil contact, rhizomes should be planted at a depth of 5-10 centimeters. Planting is typically done in late spring after the last frost. April – May is the recommended planting time, and a longer growing season in the first year helps rhizome growth. Early planting takes advantage of springtime soil moisture and allows an extended first season of growth and enables larger rhizome systems to develop.

Nitrogen, phosphorus, and potassium are three key nutrients that are vital for growth of MG and can be applied any time before or after planting. Water is also vital for rhizome growth, so irrigation is highly recommended in drier areas. Weed control is very critical for MG, especially in the early establishment stage. Competition from weeds could lower the establishment rate or even cause a complete establishment failure for the MG stand. For land is to be converted from fallow or forage, weed control should be started the year before rhizome planting by pre-planting herbicide tolerant crops followed by a winter cover crop. In the spring of the planting year, tillage, burndown, and application of a pre-emergence herbicide are recommended to help control weeds. Once properly established, the MG stand can outperform weeds and should not require any herbicide application after establishment (year 2 and beyond). Fertilizer amounts in the first year are recommended at the same level as would be applied for growing corn. From the second-year forward, fertilizer application is linked to the removal of nutrients through harvesting, and there is a recommended rate by USDA (2011) accounting for the removal of each dry ton of MG biomass during harvest.

Based on growing conditions, MG dry-matter yields range from 15-25 t/he with lower yields at more northern latitudes due to harsher winters. Harvest can occur in the second year and can be carried out for an estimated 20 years before the field needs to be replanted.  After growing vigorously during the summer, MG stops growing during autumn. The leaves drop off the crop and the stems dry as the winter proceeds reaching a moisture content of approximately 30% the following spring. Harvesting is optimal when the moisture content is less than 20% and when it is easier to store MG, also the calorific value of biomass increases with decreasing moisture content. Early harvesting can produce a product with high moisture and leaf content which will be unsuitable for many applications. Delayed harvesting can damage the new growth of the emerging crop. Consequently, the optimum time of harvest is between these two extremes. MG can be harvested by mowing and baling or can be cut and chipped. Harvesting of biomass can be done with a silage harvester or a mower-conditioner if baled. When harvesting, 5-10 centimeters of stubble should be left in the field to reduce moisture and soil content in the biomass bales by avoiding contact with the soil and picking up leaf litter. Overall, caution while harvesting is required to produce clean bales to deliver to the energy plant for combustion or processing.

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