*5.1.3. Ecological demands*

Because of its C4 photosynthetic pathway and perennial rhizome, *M. giganteus* exhibits a very good combination of radiation, water, and N-use efficiencies for biomass production [44]. Boehmel et al. [45] compared the N-use efficiency of different annual and perennial energy crops and concluded that *M. giganteus* showed a higher N-use efficiency value of 526 kg DM kg−1 when compared to the N-use efficiency of maize (65 kg DM kg−1). *M. giganteus* can be grown on a wide range of soils. The most important soil characteristic is the water holding capacity; therefore, sites with stagnant water are unsuitable. The highest yields have been reported in soils with a good water holding capacity. *M. giganteus* begins growth from the dormant winter rhizome when soil reaches temperatures of 10–12°C [46].

#### *5.1.4. Biomass yields and characteristics*

The production of aerial biomass depends on the duration of the growth period. After the first year, the start of the growing season depends on the last frost of spring. On the other hand, the end of the growing season depends on the flowering or the first autumn or winter, according to the date of harvest or location [47].

characteristics and quality of miscanthus are mainly a function of location and genotypes. For example, Lewandowski et al. [11] found that the ash contents of the biomass are correlated with high silt and clay content of the soil. In central Europe, miscanthus is harvested at the beginning of spring because the stems are dried during the winter and part of the ash, Cl, and K are leached by precipitation, which substantially improves the quality of the combustion. The most important management tool to improve biomass quality in miscanthus as a fuel is

**Common name Giant** *Miscanthus* **Switchgrass Reed canarygrass Giant reed** Scientific name *Miscanthus x giganteus Panicum virgatum* L. *Phalaris arundinacea* L. *Arundo donax* L.

> Wide range. Drought tolerant. Does not grow well in wet areas

Day length Long-day plant Short-day plant Long-day plant Long-day plant

15–60 15–20 10–23

Ash (%)\* 1.6–4.0 4.5–10.5 1.9–11.5 4.8–7.8

5–40 5–34 7–14 3–37

17–20 17 17–19 15–19

1020 1016 1100–1650 1100

Wide range. Drought tolerant, tolerant to wet areas

Wide range. Prefers well-drained soils with good water supply; also on saline soils

7

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Photosynthetic pathway C4 C4 C3 C3

tolerant to flooding. No soil compactation

The main advantages of *M. giganteus* as an energy crop are exceptional adaptability to different edaphoclimatic conditions; feasibility for growing on poor quality soils; high dry matter yields per unit surface; outstanding disease and pest resistance (application of pesticides is not necessary); very low fertilization requirements; herbicides are applied only during the first 2 years of establishment of the crop; and can be grown without any pest or weed control management once the crop is established [50, 51]. The main constrains of *M. giganteus* are its high establishment costs, its poor overwintering at some sites, and the insufficient supplies of water available in southern regions of Europe. It has been found that *M. giganteus* shows very little genetic diversity due to its sterility and vegetative mode of propagation. Most of the clones found in this species were obtained directly from the "Aksel Olsen" clone, as shown by isozyme and DNA studies [52, 53]. The small genetic base of *M. giganteus* is responsible

a delayed harvest.

*5.1.5. Miscanthus as a bioenergy crop*

**Table 1.** Perennial grasses species with potential as energy crop.

Soils Wide range. Not

Biomass yields (t ha −1)\*

Kg −1) \*

(°C)

\*Dry matter

Moisture content at harvest (%)

High heating value (MJ

Ash fusion temperature

The lifetime of the crop lasts approximately 20 and 25 years [11], during which biomass is produced during two phases: a yield-building phase, which lasts for 2–5 years, depending on climate and plant densities, and a plateau phase where the yield is maintained [48]. When crop water supplies are not limiting, maximum crop yields are reached more rapidly in warmer climates than in cooler climates [47].

Miscanthus stands need between 3 and 5 years to become fully established and reach the maximum yield level [11]. Biomass yields above 30 t DM ha−1 have been reported in southern European locations with a high incidence of annual global radiation and high average temperatures, but only under irrigation conditions. Maximum yields of up to 49 t DM ha−1 have been observed in Europe during an autumn harvest of mature crops with irrigation. Harvestable yields in the spring are 27–50% lower than those in the autumn [49].

The main characteristics of miscanthus biomass as a fuel are listed in **Table 1**. The main problem of miscanthus biomass as fuel is its relatively low ash-melting point (1020°C). Biomass


**Table 1.** Perennial grasses species with potential as energy crop.

characteristics and quality of miscanthus are mainly a function of location and genotypes. For example, Lewandowski et al. [11] found that the ash contents of the biomass are correlated with high silt and clay content of the soil. In central Europe, miscanthus is harvested at the beginning of spring because the stems are dried during the winter and part of the ash, Cl, and K are leached by precipitation, which substantially improves the quality of the combustion. The most important management tool to improve biomass quality in miscanthus as a fuel is a delayed harvest.

#### *5.1.5. Miscanthus as a bioenergy crop*

of *Miscanthus sinensis* and *M. sacchariflorus*. This natural hybrid is a giant, perennial warmseason grass native to Asia that is generating much enthusiasm for extremely high yields and

*Miscanthus × giganteus* is a sterile hybrid that does not produce viable seed and therefore propagates vegetatively underground through its rhizomes (by planting underground stems). The rhizomatous C4 grass has been considered as a strong candidate as an energy crop due to its potential to deliver high biomass yields (up to 30 ton ha−1) under low input conditions, and its

Because of its C4 photosynthetic pathway and perennial rhizome, *M. giganteus* exhibits a very good combination of radiation, water, and N-use efficiencies for biomass production [44]. Boehmel et al. [45] compared the N-use efficiency of different annual and perennial energy crops and concluded that *M. giganteus* showed a higher N-use efficiency value of 526 kg DM kg−1 when compared to the N-use efficiency of maize (65 kg DM kg−1). *M. giganteus* can be grown on a wide range of soils. The most important soil characteristic is the water holding capacity; therefore, sites with stagnant water are unsuitable. The highest yields have been reported in soils with a good water holding capacity. *M. giganteus* begins growth from the dormant win-

The production of aerial biomass depends on the duration of the growth period. After the first year, the start of the growing season depends on the last frost of spring. On the other hand, the end of the growing season depends on the flowering or the first autumn or winter, according

The lifetime of the crop lasts approximately 20 and 25 years [11], during which biomass is produced during two phases: a yield-building phase, which lasts for 2–5 years, depending on climate and plant densities, and a plateau phase where the yield is maintained [48]. When crop water supplies are not limiting, maximum crop yields are reached more rapidly in warmer

Miscanthus stands need between 3 and 5 years to become fully established and reach the maximum yield level [11]. Biomass yields above 30 t DM ha−1 have been reported in southern European locations with a high incidence of annual global radiation and high average temperatures, but only under irrigation conditions. Maximum yields of up to 49 t DM ha−1 have been observed in Europe during an autumn harvest of mature crops with irrigation.

The main characteristics of miscanthus biomass as a fuel are listed in **Table 1**. The main problem of miscanthus biomass as fuel is its relatively low ash-melting point (1020°C). Biomass

Harvestable yields in the spring are 27–50% lower than those in the autumn [49].

very high cold tolerance.

6 Advances in Biofuels and Bioenergy

*5.1.3. Ecological demands*

*5.1.2. General species description*

economic as well as environmental benefits [41–44].

ter rhizome when soil reaches temperatures of 10–12°C [46].

*5.1.4. Biomass yields and characteristics*

to the date of harvest or location [47].

climates than in cooler climates [47].

The main advantages of *M. giganteus* as an energy crop are exceptional adaptability to different edaphoclimatic conditions; feasibility for growing on poor quality soils; high dry matter yields per unit surface; outstanding disease and pest resistance (application of pesticides is not necessary); very low fertilization requirements; herbicides are applied only during the first 2 years of establishment of the crop; and can be grown without any pest or weed control management once the crop is established [50, 51]. The main constrains of *M. giganteus* are its high establishment costs, its poor overwintering at some sites, and the insufficient supplies of water available in southern regions of Europe. It has been found that *M. giganteus* shows very little genetic diversity due to its sterility and vegetative mode of propagation. Most of the clones found in this species were obtained directly from the "Aksel Olsen" clone, as shown by isozyme and DNA studies [52, 53]. The small genetic base of *M. giganteus* is responsible for the fact that the same clone has almost always been used in most studies or for cultivation. The sterility of *M. giganteus* is particularly interesting because it prevents the risk of invasion of the species; but on the other hand, it is a limitation to improve biomass production and to adapt it to a wide range of climatic conditions [47]. The sterile hybrid *M. giganteus* has to be propagated asexually using plantlets produced in tissue culture (micropropagation) or by rhizome divisions (macropropagation). The optimal planting density is one to two plants per square meter [11]. It has been reported that irrigation during the first growing season significantly improves the establishment rates.

*5.2.2. General species description*

considered to be lower than that of miscanthus [11].

cultivars are tetraploid or hexaploid [62].

*5.2.3. Ecological demands*

term waterlogging.

areas that receive run-on water.

soil temperature is below 15.5°C [63].

Switchgrass is one of the best herbaceous energy crops due to its habit of perennial growth, high yield potential on a wide variety of soil conditions, and compatibility with conventional agricultural practices [59]. Switchgrass has a deep rooting system that contributes to the accumulation of organic matter in the soil and, therefore, carbon sequestration [60]. In full development of the plant, the underground biomass is similar or even greater than the aerial biomass.

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Switchgrass can be established through seeds; therefore, it has lower production costs that make it a practical option among the energy crops. However, the switchgrass biomass yield is

Switchgrass can grow to more than 3 m height and develop roots to a depth of more than 3.5 m. The inflorescence is a typical open and diffuse panicle of 15–55 cm long. Each panicle consists of many to hundreds of spikelets at the end of long branches, with two dissimilar florets in each spikelet [61]. The expected life of a pasture would be 10 years or more if properly managed. Switchgrass is a cross-pollinated plant that is largely self-incompatible, and most

Switchgrass will grow best on well-drained good quality soils but will also sustain lower quality soils and shallow rocky soils. It can grow on sand to clay loam soils and tolerates soils with pH values ranging from 4.9 to 7.6 [63]. It is drought tolerant, but the grass does not grow in locations where precipitation is below 300 mm per year. Switchgrass can tolerate short-

Switchgrass can be categorized into two groups or ecotypes classified by their habitat preference: the upland ecotype and the lowland ecotype. Upland ecotypes occur in upland areas that are not subject to flooding, while lowland ecotypes are found on floodplains and other

The upland ecotype is generally thinner stemmed and shorter than lowland ecotypes, is adapted to drier and wetter environments, and is generally derived from accessions collected in the northern regions of North America. Lowland plants have a later heading date and are taller with larger and thicker stems. Lowland ecotypes are tetraploids, while upland ecotypes are either octoploids or tetraploids. There are ecotypical differences among switchgrass ecotypes for important compositional features, such as fiber, nitrogen, and ash, among others. Dry matter produced by lowland ecotypes has higher cellulose and hemicellulose contents and lower N and ash contents than upland ecotypes, and dry matter produced by upland ecotypes contains higher lignin contents [64]. Upland and lowland tetraploids have been crossed to produce F1 hybrids that have an increase in yield of 30–50% over the parental lines. These hybrids are promising sources of high yield biomass cultivars [64]. Most seedlings of switchgrass will germinate after 3 days at 29.5°C. However, they germinate very slowly when the

Miscanthus does not respond to N fertilization at several sites in Europe; therefore, N fertilization is necessary only on soils with low N contents. Weed control in miscanthus in the year of planting is crucial for establishing a successful and healthy stand. The first 2 years are most critical, with little weed management thereafter. There are very few labeled herbicides for use on miscanthus crop, but various herbicides suitable for use in maize or other cereals can be used. It can be harvested only once a year, and the harvest window depends on the local conditions. The later the harvest can be made, the better the quality of the combustion, since it will decrease the moisture content and the mineral content of the biomass.

However, there is a trade-off between improving the quality and yield, since yield losses of up to 35% can occur between maximum yield and late harvest in early spring [54]. From an economic point of view, a late harvest with biomass water content lower than 30% is recommended in order to reduce the costs for harvesting and drying of the biomass [55]. Bilandzija et al. [1] state that harvest delays, from autumn to spring, had statistically significant influence on moisture, C, H, O, N, and S contents. They found that delayed harvest enhanced the quality of biomass in terms of combustion process, primarily through lowering moisture content, which is particularly important if biomass producers do not have drying systems.

Given its potential to be exploited for energy purpose, *Miscanthus × giganteus* is presently used mostly for electricity or heat generation in direct combustion [56], mostly in the form of wood chips, pellets/briquettes, and bales [57]. It is estimated that replacing fossil fuels with biomass from *Miscanthus × giganteus* can enable reducing the CO2 emission by 75–93% [48]. However, because there is presently only one commercially available clone, *Miscanthus × giganteus*, it has some limitations such as a lack of winter hardiness during the establishment period [7] and it needs to be propagated vegetatively resulting in high field plantation costs.

#### **5.2. Switchgrass**
