About Cenchrus purpureus (Schumach.) Morrone
Cenchrus purpureus, commonly called napier grass or elephant grass, is a monocot C4 perennial grass in the Poaceae grass family. It grows tall and forms large, robust bamboo-like clumps. This species is heterozygous, but its seeds rarely fully develop, so it most often reproduces vegetatively via stolons—horizontal shoots that grow above the soil, extending from the parent plant to produce new offspring. It has low requirements for water and nutrient inputs. Elephant grass has been crossed with pearl millet to create the hybrid Bajra Nappier, and further work has been done to reduce the internode length of elephant grass. Napier grass plantations produce approximately 40 tonnes of dry biomass per hectare per year, with an average energy content of 18 GJ (5 MWh) per tonne, and the grass can be harvested multiple times per year. When used as animal fodder, its main use, the grass is generally harvested at relatively short intervals of every 1 to 3 months. When used for bioenergy, it is harvested at longer intervals of 4 to 12 months. Longer harvest intervals increase the stem-to-leaf ratio, which makes the forage harder for animals to chew and digest, but annual dry yield often increases with longer intervals. After 4 months of growth, napier grass can reach a height of 7 to 8 meters. It grows best between 25 and 40 °C, shows little growth below around 15 °C, and stops growing entirely at 10 °C. While frost kills the above-ground portions of the plant, it regrows when warm, moist conditions return. Napier grass grows at elevations ranging from sea level to over 2,000 meters. While it can be propagated from seeds, inconsistent seed production makes seed collection difficult. As an alternative propagation method, it can be planted using stem cuttings taken from stolons. These cuttings can be planted by inserting them along furrows spaced 75 cm apart, both within rows and between rows. Napier grass is the most important fodder crop for dairy farmers in East Africa, and its high productivity makes it especially well-suited for feeding cattle and buffaloes. Hairless varieties such as the Ugandan hairless cultivar have much higher value as fodder. Because it can grow with little water and nutrients, grazing napier grass allows arid lands to be used productively for food production. It is also used as a trap plant in the pull-push management system, which incorporates livestock for additional economic value. For African landscapes, napier grass is valuable because it prevents soil erosion. It can also be used as a fire break, a wind break, and to improve soil fertility. More recently, napier grass has been used to reduce pressure on food production for bioenergy, since 2 billion hectares of non-arable land is suitable for growing energy crops. Thermal pyrolytic conversion can be used to process napier grass into charcoal, biogas, and bio-oil. Although this technology is not currently in widespread use, it could be implemented to provide energy to African communities while also enriching local soils. Napier grass is also used directly as a fuel source. Its young leaves and shoots are edible, and are cooked to make soups and stews. A Dutch company has processed the grass into a plastic suitable for use in packaging.
