Elephant grass (Pennisetum purpureum Schumach.) is a major tropical grass. It is one of the highest yielding tropical grasses. It is a very versatile species that can be grown under a wide range of conditions and systems: dry or wet conditions, smallholder or larger scale agriculture. It is a valuable forage and very popular throughout the tropics, notably in cut-and-carry systems (Mannetje, 1992; FAO, 2015).

Morphology

Elephant grass is a robust, rhizomatous, tufted perennial grass. It has a vigourous root system, developing from the nodes of its creeping stolons. The culms are coarse, perennial, and may be up to 4-7 m in height, branched above. Elephant grass forms dense thick clumps, up to 1 m across. The leaves are flat, linear, hairy at the base, up to 100-120 cm long and 1-5 cm wide, with a bluish-green colour. The leaf margin is finely toothed and the leaf blade has a prominent midrib. The inflorescence is a stiff terminal bristly spike, up to 15-20 cm in length, yellow-brown to purplish in colour. Spikelets are arranged around a hairy axis, and fall at maturity. Spikelets are 4-6 mm long and surrounded by 2 cm long plumose bristles. There is little or no seed formation. When seeds are present they are very small (3 million seeds/kg) (CABI, 2014; Francis, 2004; Mannetje, 1992; uke, 1983). Elephant grass is very similar in appearance to sugarcane (Saccharum officinarum) but its leaves are narrower and its stems are taller (DAFF, 2014).

Utilisation

Elephant grass is a very important forage in the tropics due to its high productivity. It is particularly suited to feed cattle and buffaloes. Elephant grass is mainly used in cut-and-carry systems ("zero grazing") and fed in stalls, or made into silage or hay. Elephant grass can be grazed, provided it can be kept at the lush vegetative stage: livestock tend to feed only the younger leaves (FAO, 2015). Elephant grass, as implied by its name, is an important source of forage for elephants in Africa (Tchamba et al., 1993; Francis, 2004).

Elephant grass is a multipurpose plant. The young leaves and shoots are edible by humans and can be cooked to make soups and stews (Burkill, 1985). The culms can be used to make fences, and the whole plant is used for thatch. It is considered a potential second generation energy source crop in the USA (EPA, 2013). Leaf and culm infusions are reported to have diuretic properties (uke, 1983). Elephant grass has several environmental applications. It can be used to make mulch and to provide soil erosion control. It is a weed controller and, in Africa, it has been reported to be used as a trap plant in push-pull management strategies to fight against stemborers in maize crops (see Environmental impact below) (Khan et al., 2007).

Many cultivars of elephant grass have been developed worldwide to suit local conditions and there is a wide range of habits, yield potential and nutritive value. "Merker" types have numerous relatively thin stems, narrow largely glabrous leaves, high yields, and are resistant to Helminthosporium. Dwarf cultivars ("Merkeron" and "Mott", developed at the Tifton Station in 1955 and 1988 respectively) are leafy and of high feed value (ook et al., 2005). Elephant grass has the capability to exchange alleles with other Pennisetum species, and several hybrids have been developed. Hybrids of pearl millet (Pennisetum glaucum) and elephant grass ("King grass", "Pusa Giant", "Bana grass", "Florida" and others) benefit from the desirable characteristics of pearl millet such as vigour, drought resistance, disease tolerance, forage quality and seed size, whereas elephant grass provides rusticity, aggressiveness, perennity, palatability and high DM yield (imbo et al., 2010).

Elephant grass originated from sub-Saharan tropical Africa (Clayton et al., 2013). It has been introduced as forage into most tropical and subtropical regions worldwide. It was introduced into the USA in 1913, in the 1950s into Central and South America and the West Indies, and in the 1960s into Australia. It is commonly naturalized and sometimes becomes invasive (CABI, 2014). Elephant grass in mainly found from 10 °N to 20 °S. It is often regarded as a weed in crops, along roadsides, waterways, wetlands, floodplain, swamps, forest edges, disturbed areas and wastelands (CABI, 2014; Francis, 2004). It can withstand drought conditions and is a pioneer species in arid lands such as the Galapagos Islands (CABI, 2014).

Elephant grass is a summer growing grass that grows from sea level up to an altitude of 2000 m (Francis, 2004). It does well in places where temperatures range from 25 °C to 40 °C (FAO, 2015) and where annual rainfall is over 1500 mm. It stops growing below 15 °C and is sensitive to frost, though it can regrow from the stolons if the soil is not frozen (uke, 1983). Elephant grass is tolerant of drought and will grow in areas where the rainfall range is 200-4000 mm. Elephant grass is not tolerant of flooding and prefers well-drained soils. With poor drainage, it is best grown on raised beds (öhl, 1982). It does better on rich, deep soils, such as friable loams, but can grow on poorly drained clays, with a fairly heavy texture, or excessively drained sandy soils with a pH ranging from 4.5 to 8.2 (FAO, 2015; ook et al., 2005; uke, 1983). Elephant grass is a full sunlight species that can still produce under partial shade but does not withstand complete shade under a dense tree canopy (Francis, 2004).

Establishment and yields

Elephant grass produces very few seeds and is mostly propagated vegetatively through stem cuttings consisting of at least 3 nodes, 2 of which are buried in rows. Row width ranges from 50 to 200 cm and distance within rows is between 50 and 100 cm (Mannetje, 1992). After planting, elephant grass grows vigorously and can reach 4 m in 3 months (kerman et al., 1990). Elephant grass is fast growing and has a high annual productivity that depends on the climatic conditions, especially temperature and rainfall (Aroeira et al., 1999; rtus-Poliakoff et al., 1991). Elephant grass requires high levels of fertilizer and a regular water supply (Mannetje, 1992). Yields range from 20 to 80 t DM/ha/year under high fertilizer inputs (Francis, 2004; kerman et al., 1990). With no, or inadequate, fertilizer, yields are in the range of 2-10 t DM/ha/year (ogdan, 1977). Cuttings can be made at 45-90 day intervals, depending on location (FAO, 2015).

Association

Though elephant grass is mainly grown in pure stands, it can be cultivated in association with legumes such as puero (Pueraria phaseoloides), centro (Centrosema pubescens), perennial soybean (Neonotonia wightii) and leucaena (Leucaena leucocephala) (Mannetje, 1992). Such associations have higher nutritional value than elephant grass alone and can produce higher DM yields, suppress weeds and improve soil fertility. In central Kenya, a comparison of three legumes (Desmodium intortum, Macrotyloma axillare, Neonotonia wightii) associated with elephant grass concluded that Desmodium intortum was the best choice whereas Neonotonia wightii gave the lowest performance (Mwangi et al., 2004). Elephant grass is sometimes intercropped with banana and cassava in home gardens (Mannetje, 1992).

Fresh grass

The ideal harvest regime depends on the cultivar, weather conditions, soil fertility, management practices and livestock needs. In Kenya, the recommendation is to harvest elephant grass for the first time when it attains a height of 1-1.2 m, usually 3-4 months after planting. Thereafter the grass should be harvested at intervals of 6 to 8 weeks, at the same height. Well-managed elephant grass can be harvested every month in hot and wet environments, or every 2 months in drier areas. Harvesting at longer intervals produces higher DM yields but lower quality forage as protein and ash content, digestibility and leaf-to-stem ratios decline. Leaving 10-15 cm high stubble provides sufficient carbohydrate reserves for subsequent regrowth (Orodho, 2006).

Elephant grass is often fed fresh in cut-and-carry systems. It can be manually or mechanically chopped prior to feeding to reduce the selection of leaves and stems by the animal. Chopping and then wilting in the sun for several hours reduces moisture, stimulates appetite, facilitates rumination and thus improves forage utilisation (Moran, 2011).

Pasture

When used for pasture, elephant grass should be heavily grazed so that most of the young leaves and shoots, which have the highest nutritive value, are available to ruminants. Grazing at 6-9-week intervals at a height of about 90 cm gives good utilization. Nitrogen can be applied after each grazing or cutting in high-rainfall areas. Any coarse, leafless stems should be mowed (FAO, 2015).

Hay and dry grass

When elephant grass is intended for hay it should be cut at an early stage of maturity as the stems become too coarse when the plant ages. In Taiwan, elephant grass is used for the production of dehydrated grass pellets used as a supplementary stock feed (Manidool, personal communication cited by ">FAO, 2015).

Silage

Elephant grass can be processed into high quality silage and may be ensiled alone (FAO, 2015). However, its high cell wall content and low concentration in water soluble carbohydrates (WSC) impair the ensiling process. In Zimbabwe, it was concluded that elephant grass should be harvested for ensiling between 6 and 7 weeks, at the peak of WSC concentration, to increase DM content and optimize herbage production without affecting nutritive value. In practice, the high moisture of elephant grass when its nutritive value is highest is an obstacle for using it as silage, because it results in undesirable fermentation with considerable nutrient losses (Manyawu et al., 2003a). For these reasons, elephant grass is often ensiled with materials that improve the quality of the silage and its nutritional value (protein or energy). The following table lists materials cited in the literature.