Imperata cylindrica (L.) Beauv.

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Graminae

Common names

Var. major: alang-alang or lalang (Malaysia), kunai (New Guinea), blady grass (Australia), cotton wool grass, spear grass (Nigeria). Var. africana: silver spike (southern Africa), cogon grass (Philippines), cotranh (Viet Nam), illuk (Sri Lanka), yakha (Laos), gi (Fiji), sword grass (Zaire).

Description

A perennial up to 120 cm high with narrow, rigid leaf-blades. Lower leaf-sheaths bearded at the mouth, upper usually glabrous; blades glabrous or hairy on the lower part, up to 100 cm long, often less, usually 3-10 mm wide, expanded; panicle 5-10 cm long; spikelets surrounded by hairs 1015 mm long. Imperata roots penetrated to 58 cm in alluvial soil at Varanasi, India, with a production of 20 480 kg air-dried roots per hectare (Ramam, 1970). There are five varieties. 1. cylindrica var. africana has the culm nodes usually glabrous and the spikelets 5 mm long, while in var. major the culm nodes are bearded and the spikelets to 3.5 mm long (Napper, 1965). Var. europaea occurs in Europe, var. Latifolia in Tibet and var. condensata in Chile (Hubbard et al., 1944).

Distribution

India, Australia, eastern and southern Africa and other warm temperate and tropical regions of the world.

Altitude range

Sea-level to 2 000 m in the Himalayas.

Rainfall requirements

It grows over a wide rainfall range of 250-6 250 mm, with maximum performance over 1 500 mm.

Drought tolerance

It can survive quite long droughts because of its rhizomes.

Soil requirements

It generally occurs on light-textured acid soils with a clay subsoil, but can tolerate a wide range of soils from strongly acidic to slightly alkaline, with a pH of 4.0-7.5, but germination is promoted by a pH of less than 5.0 (Sajise, 1973).

Ability to spread naturally

It spreads readily by rhizomes and seed. If the rhizomes are cut by cultivation, propagation can take place from pieces with as few as two nodes.

Seedling vigour

It establishes well in a burn.

Vigour of growth and growth rhythm

More than 80 percent of shoots originate from the rhizomes less than 15 cm below the soil surface (Ivens, 1970).

Response to defoliation

It cannot stand continuous heavy grazing and in Thailand it is superseded by weeds if grazed very heavily. Repeated cutting and rolling will weaken the stand and the rhizomes can be destroyed by systematic cultivation.

Grazing management

If the grass is not to be eradicated, it can be burnt periodically and grazed rotationally when 15-25 cm high.

Dry-matter and green-matter yields

In Indonesia it was found that the average number of shoots of Imperata at the places studied was 4.5 million per hectare, producing 11 500 kg of leaves and 7 000 kg of rhizomes (Soerjani, 1970). Chadokar (1977) followed the nutritive value of Imperata cylindrica at two-week cutting intervals after burning at Erap, Papua New Guinea.

Suitability for hay and silage

Most of the hay material is used for thatch and is not for fodder. It can be used as low-quality roughage in conjunction with concentrates (Soewardi et al., 1974).

Diseases

No major diseases affect it.

Optimum temperature for growth

30°C, maximum 40°C.>

Minimum temperature for growth

20°C.a

Ability to compete with weeds

Imperata competes very successfully with weeds and suppresses them, but it is an important weed in its own right.

Pests

In Indonesia, a gall fly (Urseoliella javanica) attacks the apical meristem (Soerjani, 1970) but is itself heavily parasitized by a Chalcid wasp which destroys some 50 percent of the larvae. It exerts some biological control.

Palatability

It is eaten by livestock in the young stage, but avoided in the mature state. Elephants eat it in the Queen Elizabeth National Park, Uganda, during the dry season (Field, 1971). The extreme point and the margins of the leaves are sharp, causing irritation in the mouth, so cattle do not like it (Soerjani, 1970). The rhizomes are eaten by pigs.

Chemical analysis and digestibility

Göhl (1975) lists analyses from Pakistan, India and Malaysia.

Natural habitat

Subhumid and humid grassland and open woodland.

Tolerance to flooding

It cannot stand continuous flooding and flooding is one method of control.

Fertilizer requirements

Chadokar (1977) found that yields of Imperata responded markedly to increased nitrogen rates, but nitrogen had less effect on improving the protein content.

Compatibility with other grasses and legumes

It usually forms a monospecific sward by repeated burning. Bor (1960) stated that in the Philippines the leguminous shrub Leucaena leucocephala can grow with it and upgrade its forage value.

Genetics and reproduction

2n=20 (Fedorov, 1974).

Economics

It covers more than 16 million hectares of waste land in Indonesia, with an annual increase of more than 150 000 hectares. Another 23 million hectares are still used for shifting cultivation, which serves as a source of area increase, and shifting cultivation increases by 100 000 hectares annually. It is a noxious weed in rice, cotton, coffee, cinchona, tea, oil-palm, coconut, rubber and teak plantations. It is used for soil erosion control, mulch in coffee plantations, fodder, thatching, paper-making, packaging, fuel, ornamental purposes and for the sacrificial thread of the Hindu and as a bouquet material in the marriage ceremony in Java (Soerjani, 1970). The rhizomes and root extracts are used medicinally. In Lesotho rhizomes are eaten raw by herders and are used as a remedy for chest colds in children.

Animal production

The young shoots make good pasture (Henty, 1969). In Papua New Guinea, Holmes, Lemerle and Schottler (1976) recorded liveweight gains of 0.22, 0.25, 0.21 and 0.20 kg per day at stocking rates of 0.78, 0.94, 1.25 and 1.64 beasts per hectare for heifers grazing Imperata pasture, compared with the highest weight gain of 0.45 kg per day for heifers grazing a Hamil grass/legume pasture at a stocking rate of 1.69 and 2.17 beasts per hectare. In the Philippines, Magadan, Javier and Madamba (1974) recorded live-weight gains of cattle grazing Imperata at a stocking rate of one beast per hectare as 0.27 kg per day or 100 kg per year compared with the gain on Para/ centro pastures, which was more than three times this figure. In Florida, 52.4 kg beef per hectare were produced from grass alone. Imperata mixed with Panicum repens, unmanured, yielded 61.9 kg/ha. In the Thai highlands (Falvey & Andrews, 1979) the local cattle gain was about 16 kg live-weight gain per animal per year.

Further reading

Falvey, 1980; Falvey, Hengmichai & Hoare, 1979; Soerjani, 1970.

Dormancy

There is no dormancy. Germination of the seed in the dark increased from 9 percent at 20°C, to 55 percent at 30°C, declined somewhat at 35°C, and was about 70 percent in the light with alternate 12-hour periods at 20 and 30°C. 0.2 percent KNO3 solution increased germination in the dark, but not in the light. Germination declined gradually after 13 months' storage (Dickens & Moore, 1974).#S

Value for erosion control

It is effective in controlling erosion, but there are more useful fodder grasses which can also stabilize the soil. In eastern Nepal, of four grasses tested for soil binding ­ Imperata cylindrica, Brachiaria mutica, Cynodon plectostachyus and Cymbopogon spp. ­ Imperata produced the most "roots" (rhizomes and roots): 3 620 kg DM/ha in the top 7.5 cm of soil in its second year of growth and 4 574 kg/ha in its third year (Khybri & Mishra, 1967). It is used for stabilizing mine dumps in Zimbabwe (Hill, 1972).

Tolerance to fire

Frequent fires encourage the uniformity of an Imperata sward, and generally it occurs as a fire disclimax. The leaves burn readily, and regrowth from rhizomes is rapid (Chadokar, 1977).