**5. Napier grass**

large production of seeds, easy to grow nature, and status as a feedstock. There are few

*Cynodon sp*.: *Cynodon sp*. includes perennial grasses referred to as Bermuda grass or star grass, which are commonly grown in the topics and subtropics of the Americas, Africa, and South-East Asia [16]. Generally, they have been used for forage or as fodder for bioenergy [17]. Though Rengsirikul et al. [18] refer to Tifton grass as a type of Napier grass [18], Tifton grass is a specific breed of Bermuda grass (*Cynodon dactylon* L.) from Tifton, Georgia, USA, that was bred for its

*Digitaria decumbens*: Pangola grass, scientific name *Digitaria decumbens* or *Digitaria eriantha*, is a forage grass originating from South Africa that is currently grown worldwide in the Americas, Africa, Oceania, Australia, and Asia [19]. It has been grown in Thailand since 1983 due to its success as fodder for grazing animals and its ability to grow on lands that previously

*Miscanthus sinensis*: Miscanthus grass was generally called as Chinese silvergrass. Its scientific name is *Miscanthus sinensis*. Chinese silvergrass is native to eastern Asia, including Thailand. It is a perennial and clumping grass and also grown in some parts of the Americas and Europe. The grass can grow up to 2–3 meters tall [20]. Nowadays, this grass is used as cattle fodder

*Panicum maximum*: Purple guinea grass, or *Panicum maximum* cv. Tanzania, is originally from the Ivory Coast of Africa. It is another perennial grass with a high protein content that is currently used as a feedstock for grazing animals in Thailand, having been introduced to the

*Paspalum atratum*: Atratum grass, known by its scientific name *Paspalum atratum*, is a perennial grass that can grow 1–2 meters tall. It originated in South America and is now cultivated in the Americas, South-East Asia, and Australia, generally near the equator. Though atratum grass has low drought tolerance, it is popularly grown in Thailand due to its ability to flourish

*Pennisetum polystachyon*: Mission grass (*P. polystachyon*) is originally grown in tropical Africa. But for the past few decades, the grass has been spread throughout Africa, Asia, Australia, and Oceania. It can grow roughly 3 meters tall and is commonly known as a weed. The grass is a perennial and clumping grass. Mission grass is considered as an established weed that is

*Pennisetum purpureum: Pennisetum purpureum* Schumacher, more often referred to as Napier grass or elephant grass, is a perennial grass native to Africa that has since been cultivated in tropical areas in Asia, Oceania, and the Americas. Napier grass is a hardy grass that can grow up in clumps up to seven meters in height and is particularly important as a forage and pasture grass, erosion inhibitor, mulch, and as a windbreak for other crops. Due to Napier grass's attractive qualities, such as good productivity, high yields, and drought tolerance, several types of Napier grass have already been investigated in Thailand for their potential in bioethanol conversion to bioethanol. The types of Napier grass which were already investigated include

common, dwarf, Kamphaeng Saen, king, Muaklek, Taiwan, and WrukWona [6, 18].

draw backs like sensitivity to the dry climate and requirement of fertilizers [15].

improved digestibility as a potential biofuel feedstock [17].

and has been considered as a possible feedstock for biofuels.

currently not used for any specific purpose in Thailand [22].

during the rainy seasons and in wet soils [15].

cultivated rice [19].

158 Advances in Silage Production and Utilization

country in the 1980s [21].

Soil fertility is generally rich in Thailand. Genus Pennisetum (including Napier grass) has been reported as the most productive tropical grasses in Thailand. Eight cultivars of Napier grass, namely Dwarf, Muaklek, Bana, Taiwan A148, Common, WrukWona, Tifton and Kamphaeng Saen, are grown in Thailand. There are several cultivars regularly grown from this genus for domestic animal feed. King Napier, Bana, WrukWona, Merkerson, and the short type (Mott dwarf) are called as common Napier. It can produce highest biomass yields more than 25 t/ha/ yr dry matter when cut at 30-day intervals. In central Thailand (at Pak Chong), biomass yield was achieved at 75 t/ha/yr when cut at 60-day intervals. The scales of biomass yields demonstrated that Napier grass as a hopeful species for methane generation [18].

There is a huge awareness in the prospective utilization of Napier grass to produce ethanol in Thailand. Recently, these cultivars were selected for utilization as animal feeds, because of high leaf percentage, high nitrogen concentration, and low fiber levels. Because of its high dry matter yield, it was considered mainly as animal feed. On the contrary, for biofuels production, there is a need to get highest yield of biomass with suitability to be used either for direct combustion or for ethanol conversion. Therefore, the objectives of this paper were to quantify the yield and quality of biomass produced in different seasons by a range of Napier grass cultivars when cut at three monthly intervals throughout the year and to assess their potential as a source of energy for biofuel production in central Thailand.

In general, Rengsirikul et al. [18] confirmed that tall cultivars reach a greater length (2–4 m) than Dwarf (<1 m) with Muaklek intermediate. Furthermore, annual biomass yield was differed significantly among cultivars (**Table 2**). The tall cultivars yielded 46.3–58.4 t/ha/yr compared with 27.1 and 35.1 t/ha/yr for Dwarf and Muaklek, respectively. **Table 2** indicates that the potential of tall Napier grass cultivars to produce high biomass in Thailand to satisfy the increasing need for energy. Napier grass is tropical forage; thus, these findings can be applicable to other countries in the tropical region as well.


energy is an entirely recoverable in a closed lactic acid-dominant fermentation. On the contrary, there is negligible loss of energy; the production of ethanol by yeast during fermentation is undesirable because no acidification occurs. Correspondingly, under suboptimal ensiling conditions, secondary clostridial fermentation may lead to considerable total solids and energy losses due to extensive production of CO2 and H2 from the fermentation of lactate and hexose sugars. If grass is to be used for energy, it must be harvested and stored, usually as silage. Silage is currently made for feeding livestock, and grass silage is mostly used as co-substrate in biogas plants based on cattle, pig, or chicken manure because of its inappropriate high nitrogen content [32, 33] of about 14% of total solids. The influence of ammonia on anaerobic digestion in terms of process inhibition was found in several literatures [34–36]. However, several authors proved that monodigestion of grass silage is possible, although both applied

Grass Silage for Biogas Production http://dx.doi.org/10.5772/64961 161

Common cultivar of Napier grass was obtained from the agriculture farm which was cultivated at Mae Taeng district, Chiang Mai, Thailand. The grass was a first cut (cut at 45-day-old mature stage). Napier grass was crushed by machine into small particles. Stored grass was pulverized into small particles (1.0 mm) before use. Proximate, ultimate, chemical composition of Napier grass is shown in **Table 3**. The grass collecting and silage preparations are shown in **Figures 2** and **3**. The experiment was carried out in the Energy Research Center, School of Renewable Energy, Maejo University, Thailand. For all experiments, Napier grass (*Pennisetum purpur‐*

systems and experimental conditions differ occasionally significant.

**Property Biomass** pHa 4.85

Moisturea 77.74 Ash 3.18

Carbon (C) 44.19 Hydrogen (H) 6.00 Nitrogen (N) 2.00 Oxygen (O) 43.80 Sulfur (S) 0.06

**Table 3.** Proximate, ultimate, chemical composition of Napier grass.

**7. Biogas from Napier grass silage**

*eum*) was used as a monosubstrate.

**Proximate analysis (wt.%)**

**Ultimate analysis (wt.%)b**

As received at harvest.

Dry basis; unit % by weight.

a

b

**Table 2.** Annual dry matter (DM) yields of eight Napier grass cultivars.
