Arundo Donax or Giant Reed
Arundo donax (L.) is a tall, perennial C-3 grass species belonging to the subfamily Arundinoideae of the Poaceae family that grows in damp soils, either fresh or moderately saline. Other common names include giant reed, giant cane, carrizo, arundo, Spanish cane, Colorado River reed and wild cane. Arundo donax generally grows to 6 meters (20 ft) and in ideal conditions it can exceed 10 meters (33 ft); the hollow stems, 3 to 5 cm thick, have a cane-like appearance similar to bamboo. The leaves are alternate, 30 to 60 centimeters (12 to 24 in) long and 2 to 6 centimeters (0.79 to 2.4 in) wide with a tapered tip, are grey-green, and have a hairy tuft at the base. Overall, it resembles an outsize common reed (Phragmites australis) or a bamboo (subfamily Bambusoideae).
Giant reed is one of the most promising crops for energy production for the Mediterranean climate, where it has shown advantages as an indigenous crop, durable yields, and resistance to long drought period. Several field studies have highlighted the beneficial effect of giant reed crop on the environment due to its minimal soil tillage, fertilizer and pesticide requirements. Arundo donax is a strong candidate for use as a renewable biofuel source because of its fast growth rate, ability to grow in different soil types and climatic conditions. Once established, A. donax is known to produce an average of three kilograms of biomass per square meter (25 tons per acre) [166, 167]. The energy density of the biomass produced is 17 MJ/Kg regardless of fertilizer usage. The ability of Arundo donax to grow for 20 to 25 years without replanting is also significant [166].
Energy crops like Arundo donax can significantly mitigate carbon dioxide anthropogenic emissions, partially replacing fossil fuels. It was estimated that 1 ha of energy crop would save approximately 5 Mg of fossil carbon [168]. It is interesting to note that this perennial crop has the potential to remove carbon due to minor tillage and soil respiration losses and root biomass. The characteristic root system and root distribution of Arundo donax has the capacity to accumulate carbon stocks in the soil. Furthermore, Arundo donax has shown higher root biomass and a proportionally deeper root system compared to other energy crops such as switchgrass, Miscanthus and sorghum. In some studies it has been observed that Arundo donax maintains overall higher soil moisture levels in the upper layers than other energy crops and constant water capture capacities along the root profile [168]. Chemical analysis of Arundo donax is described in several publications and a representative analysis is presented in Table 3.15.