An appropriate forage feedstock resource is Arundo donax (further on Arundo), commonly known as ‘‘giant reed”, which is a fast-growing perennial rhizomatous grass that has an average biomass yield of 30–40 tons of dry matter (DM) per hectare per year. It can adapt to different types of soils and weather conditions, and requires very low cultivation inputs. For that reason, Arundo has been considered a promising biomass feedstock. However, Arundo goes beyond bio-refineries all the way to forage feedstock. It was first mentioned as a forage grass in 1948, and also as a forage-silage plant in 1975.
Forage Feedstock: Feeding and nutrient value
Figure 1: Arundo donax
Arundo (Figure 1) is not very palatable to livestock in general, animals graze young green shoots during the dry season. Arundo is readily browsed by cattle when young but cannot produce valuable forage as it matures very quickly and soon becomes unpalatable. Younger plants (50-100 cm height) and tips of older shoots are more palatable and of better nutritive value than older ones.
In an early study the upper and lower halves of young and old plants were analysed for nitrogen, phosphorus, calcium, magnesium, potassium, and acid hydrolysable carbohydrate. Nitrogen, phosphorus and potassium exhibited the greatest concentration in the upper half of the younger plants, while calcium and magnesium exhibited the greatest concentration in the upper parts of the older plants. Total acid hydrolysable carbohydrate was greater in the older plants, and especially so in the lower half.
Forage Feedstock: Digestibility
Due to its high fibre and low protein content, Arundo foliage takes time to digestible. Experiments that were conducted in Egypt reported 47-51% digestibility. Another study reported similar values, 50-52% for DM (dry matter) digestibility and about 54-56% for OM (organic matter) digestibility. Although a higher (69%) DM digestibility was reported in an early trial in India.
Several trials in Egypt have studied the value of the Arundo in ensiled or fresh form. Fresh Arundo forage feedstock and Arundo silage (ensiled 3% molasses on fresh basis) were better digested by Rahmani sheep than Arundo hay or Berseem hay. This can be explained by a higher microbial activity in the rumen with fresh or ensiled forages compared to the hays, as total volatile fatty acids concentration and microbial protein were higher 4 hours after the feeding. Arundo silage was found as digestible as maize silage, and better consumed than the Arundo hay or berseem (Trifolium alexandrinum) hay.
Forage Feedstock: Ensilage
Figure 2: Silo-bag
Ensilage (Figure 2) is a traditional method for storing green crops, such as corn stover, in the forage feedstock industry. During ensilage, lactic acid bacteria (LAB) break down free sugars in the biomass under anaerobic conditions, generating lactic acid, acetic acid, ethanol, and carbon dioxide. Besides, propionic acid can also be produced by propionic acid bacteria or heterofermentative bacteria during the ensilage process. The organic acids, especially lactic acid, can decrease the pH to around 4, which is low enough to inhibit growth of microorganisms.
Arundo can be harvested (Figure 3) at different times of the year. According to the literature, the harvest date can significantly affect biomass composition, such as moisture, nitrogen, mineral, and carbohydrate contents, which could further affect the performance of the subsequent ensilage process.
Figure 3: Arundo harvesting and silage, 2013
Effect of harvest date on composition of Arundo
In the study, DM (dry matter) contents of Arundo harvested in August, October, November, and December were 32%, 44%, 43%, and 50%, respectively, while the ODM (organic dry matter) contents varied slightly from 91% to 94%.
Generally, Arundo harvested at later dates (in October, November, and December) had lower moisture contents than that harvested at an earlier date (in August), thus a later harvest time could help reduce costs for biomass transportation and storage. However, it should be noted that Arundo leaves fall off in winter, which causes biomass loss.
The WSC (water soluble content, based on DM) in Arundo increased from 2.8% in August to about 5% in October, remained stable in November, and further increased to nearly 6% in December. Since WSC is the major substrate for lactic acid production by LAB (lactic acid bacteria), high WSC content generally results in high lactic acid levels and low pH during the ensilage process, which are indicators of a successful ensilage. Therefore, late-harvested Arundo (in December) may have better ensilage performance than early-harvested (in August) due to its higher WSC content.
Forage Feedstock: Effect of harvest date on changes in composition of Arundo during ensilage
About 99% of DM was preserved during 90 days of ensilage, except for the August harvested Arundo which showed a DM loss of about 8%.
Extractives and WSC contents in Arundo biomass for all harvests were reduced sharply in the first 3 days of ensilage. After 90 days of ensilage, Arundo harvested in December had more extractives and WSC remaining in the biomass and a lower pH than those harvested in August, October, and November.
Figure 4: Lactic acid bacteria
Generally, glucose and fructose in WSC are primary fermentation substrates for LAB (Figure 4). Although pentoses from hydrolysis of hemicellulose are also fermented. During ensilage of Arundo harvested on different dates, more than 60% of cellobiose and glucose were consumed in 3 days. After that, a small amount of cellobiose (about 2% of initial DM) was maintained in Arundo harvested in December, which indicates that the pH in the ensiled biomass was low enough to prevent significant consumption of the cellobiose.
During ensilage of Arundo harvested in August, October, November, and December, cellulose content in the biomass decreased by 8.6%, 5.1%, 3.6%, and 3.3%, respectively. More cellulose was preserved as the harvest date changed from August through December. Hemicellulose was easier to degrade than cellulose during ensilage, and showed decreases of 12.3% (August), 12.4% (October), 5.0 (November), and 5.0% (December). Higher hemicellulose degradation than cellulose degradation has also been observed during ensilage of other forage feedstock; such as corn stover and orchard grass.
During the ensilage process, degradation of lignin in Arundo harvested in August, October, November, and December was in the range of 4.8–6.8%. The relatively high lignin degradation in Arundo could result in improved digestibility, since lignin is the most recalcitrant component in lignocellulosic biomass.
Effect of harvest date on organic acids and ethanol production during ensilage
Lactic acid production was increased as the harvest date changed from August through December. Besides lactic acid, other organic compounds were also produced during the ensilage process, with the highest content of total organic acids and ethanol observed in Arundo harvested in November.
Arundo harvested in August showed higher acetic acid and butyric acid contents than those harvested in October, November, and December. Arundo harvested in October and November had higher propionic acid and ethanol contents than others.
Arundo harvested in August showed a low ensilage quality, as primarily evidenced by the high level of butyric acid, which is a critical indicator of an inadequate ensilage.
Forage Feedstock: Effect of harvest date on enzymatic digestibility of non-ensiled and ensiled Arundo biomass
Enzymatic digestibility of non-ensiled Arundo (Figure 5) decreased from 42% to 36% as the harvest date changed from August through December. It has been known that lignin is one of the major contributors to the recalcitrance of lignocellulosic biomass, and removal of lignin makes cellulose more accessible to enzymes and thus improves the enzymatic digestibility. The lignin content of Arundo biomass increased with later harvest dates, which could partially explain the decrease of digestibility.
Figure 5: Detailed view of the internal cellular structure of Arundo donax with perforations
During the ensilage process, enzymatic digestibility of Arundo generally increased, which was also consistent with the decreased lignin contents as. After 90 days of ensilage, Arundo was 8%, 14%, 15%, and 20% more digestible (p < 0.05) than non-ensiled Arundo harvested in August, October, November, and December, respectively. All the ensiled Arundo biomass achieved enzymatic digestibility of about 43–46%. These results indicated that ensilage can effectively improve enzymatic digestibility of Arundo with lignin removal.
Forage Feedstock: Feeding trials
Limited reports are available on feeding trials (Figure 6) of Arundo in fresh, ensiled or form.
Trials in Egypt detected that fresh Arundo forage and Arundo silage (ensiled 3% molasses on fresh basis) were better digested by Rahmani sheep than Arundo hay or berseem hay. This can be explained by a higher microbial activity in the rumen with fresh or ensiled forages compared to the hays, as total volatile fatty acids concentration and microbial protein were higher 4 hours after the feeding.
Figure 6: Feeding trial for finishing lambs
Moreover, Arundo silage was found as digestible as maize silage in feeding trials of sheeps and goats.
It was also found that silage or fresh forage fed to Zairibi goats gave higher milk yields than Arundo hay. The milk composition did not differ between diets.
When Arundo silage was fed by sheeps, better reproductive performance was detected than fresh reeds and reed hay and the results obtained were closed to those observed with berseem hay. Also ensiled and fresh Arundo forage gave better fattening performance than Arundo hay, the latter being close to berseem hay in that respect. Also blood parameters were analysed, and found similar values for all the treatments, except red blood cells which were higher for the fresh or ensiled reeds. Dressing values, carcass weight and more generally carcass quality (shoulder and leg cuts) were significantly improved with silage or fresh Arundo forage feedstock compared to berseem hay and Arundo hay.
Arundo silage had no adverse effects when fed with whole dates and olive cake in order to solve the shortage of green fodder in Egyptian oases.
Experiments conducted in India found that extracts from Arundo had anthelmintic properties (around 55% of efficacy) against gastrointestinal parasites (Ascarissp., Oesophagostomumsp. and Paramphistomumsp.) of cattle. A commercial bolus made of a mixture of several powdered plants including Arundo donax improved milk yield in dairy cows, which was attributed to the presence of components reported to be galactogogues.
If you are interested in purchasing Arundo to produce forage feedstock, do not hesitate to get in touch with us at info@arundobioenergy.com or here. Further information on forage feedstock from Arundo can be found on our website.
