Themeda triandra (PROSEA)
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Introduction |
Themeda triandra Forssk.
- Protologue: Fl. Aegypt.-Arab.: 178 (1775).
- Family: Gramineae
- Chromosome number: 2n= 20, 30, 40, 50, 60, 70, 80
Synonyms
Themeda imberbis (Retzius) Cooke (1908), T. australis (R. Br.) Stapf (in part) (1919).
Vernacular names
- Red oat grass, kangaroo grass (En)
- Indonesia: merakan lanang (Javanese)
- Philippines: bagokbok (Tagalog), samsamon (Ilokano), ipatpatey (Bontok)
- Cambodia: sbö':w
- Laos: hnaaz fèèk
- Thailand: ya-faek
- Vietnam: co' bông cao ru'[n]g khôp, co'tam hu[n]g.
Origin and geographic distribution
The natural distribution of red oat grass is pantropical/subtropical with extension into the temperate zone as a summer growing grass. It is most likely of Gondwanan origin with a predominant distribution in Australia, South-East Asia, India and Africa.
Uses
Red oat grass is used as part of the naturally occurring savanna pastures for domestic livestock production and wildlife.
Properties
In native pastures the N concentration of red oat grass ranges from 2.7% in green material from the early flush of the growing season to 0.5% in dry forage by the end of the dry season. Digestibility varies from about 60% to 35%.
Botany
A tufted leafy perennial, growing up to 1.5 m tall, erect, culms usually unbranched but quite variable in morphology, smooth, often becoming golden at maturity, nodes hairless. Leaves both basal and on the culms; leaf-sheath keeled, coarsely striate, hairless below but becoming quite short-hairy towards the ligule, the margins translucent; ligule short and membranous, later splitting into a broad rim of short hairs with some longer, marginal hairs; leaf-blade 15-50 cm × 2-5 mm, green or sometimes bluish, folded with a more or less hairy clasping base, becoming more or less flat towards the acutely pointed tip, flexuous, smooth or slightly rough down the margins. Inflorescence a loose, narrow spathate usually reddish-coloured panicle, the flexuous peduncled racemes slightly nodding; panicle branches slender and smooth, often quite widely separated along the axis and bearing clusters of one to several racemes (spikelet clusters), each at first enclosed by, and later subtended by a strongly keeled, sheath-like spathe; spikelet clusters are composed of a sessile, fertile awned spikelet surrounded by an involucre of 2 pairs of sessile and 1 pair of pedicellate male or sterile (often reduced) spikelets; florets 2 in the fertile spikelet, the lower sterile and reduced to a lemma, the upper bisexual, 1 in the involucral and pedicellate spikelets which are male, sterile or reduced to a lemma; fertile spikelet sessile and awned, about 8 mm long including the dark brown, sharply pointed, densely and stiffly hairy barbed callus; awn up to 7 cm long, puberulous, twisted and geniculate, hygroscopically active so that the seed can bore itself into the ground. Caryopsis lanceolate, channelled on one side.
The fruits ("seeds") of red oat grass fall individually to the ground. They probably have similar seed dormancy and germination control mechanisms to speargrass Heteropogon contortus (L.) Beauv. ex Roemer & Schultes and other Andropogoneae. Flower initiation is obligately to facultatively short-day in the tropics, short-day to day-neutral in the subtropics and long-day in the temperate zone. There is some evidence of a cold stratification response in materials occurring in subalpine areas, these forms also being polyploid. The reproductive system is also likely to be obligately to facultatively apomictic as in the majority of Andropogoneae.
The species is very polymorphic, and based on the hairiness of the inflorescence parts, has been subdivided repeatedly in the literature. Without clear correlations with geographic distribution, these subdivisions are of little value.
Ecology
Red oat grass is a typical andropogonoid grass of the tropical and subtropical savannas which are characterized by a marked seasonality of warm wet, and cooler dry seasons. It is a savanna grass in seasonally wet/dry climates of moderate rainfall. However, it also occurs in quite arid environments along drainage lines and run-on areas. It is relatively drought-tolerant, with its main range of distribution being within 500-1200 mm of annual rainfall. It has been recorded at above 3000 m in the Himalayas. However, an interesting departure from this is its adaptation to growing during the warm season of the temperate zone provided there is moisture at that time. In the subtropics red oat grass will produce green growth in the cool season if there is some out-of-season rainfall, which is atypical of andropogonoid grasses. However, it is sensitive to continued intensive grazing and this unseasonal growth places it at greater risk from overgrazing when almost everything else is senesced and dormant. It has been shown to be particularly sensitive to heavy grazing when the growing points are elongating late in the growing season. Like Heteropogon contortus , red oat grass responds to dry-season burning, but being more sensitive to grazing, it will predominate in areas which are burnt and not significantly grazed, e.g. some road and railway exclosures. It grows on a wide range of soil types except heavy clays.
Agronomy
The wide variety of growth forms and habitats of red oat grass makes generalizing somewhat hazardous. Its intolerance of prolonged heavy grazing is sometimes belied by areas which have survived many years of close grazing or mowing where the species has developed a prostrate growth form. Heteropogon contortus often replaces red oat grass following sustained grazing and dry-season burning.
As red oat grass is susceptible to prolonged heavy grazing pressure, it requires very careful control of grazing when used in conjunction with management practices such as oversowing legumes or provision of feed supplements such as mineral licks, urea/molasses, and other externally supplied feeds. These practices usually lead to increased grazing pressure, especially early in the growing season when red oat grass is more susceptible to defoliation than is Heteropogon contortus . This appears to be becasue of the interactive effect of defoliation with the different pattern of synchrony of growing points in these two species at the start of the growing season.
No diseases and pests of any consequence have been recorded.
The annual yield depends very much on the amount and favourable distribution of rainfall occurring during the warm season. The normal savanna environment means that growth and quality are seasonal so that there is a fluctuating amount of biomass and level of feed quality on offer for livestock grazing. Production is likely to range between 0.5-5 t/ha of DM, depending on conditions.
Genetic resources and breeding
It is unlikely that substantial germplasm collections are being maintained.
Prospects
In production systems where a stable alternative can be established, either naturally as with replacement by Heteropogon contortus , or by conversion to planted pastures, there could be little disadvantage in losing red oat grass. However, where there are no viable and acceptable alternatives or where there is the need to preserve its particular type of ecosystem, as in some national park systems, it may be important to maintain it, which requires careful management of livestock or wildlife.
Literature
- Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 286-290.
- Bor, N.L., 1960. The grasses of Burma, Ceylon, India and Pakistan. Pergamon Press, Oxford. p. 254.
- Lazarides, M., 1980. The tropical grasses of southeast Asia. Phanerogamarum Monographieae Tomus XII, J. Cramer, Vaduz. pp. 76-78.
- Mott, J.J., Ludlow, M.M., Richards, J.H. & Parsons, A.D., 1992. Effects of moisture supply in the dry season and subsequent defoliation on the persistence of the savanna grasses Themeda triandra, Heteropogon contortus and Panicum maximum. Australian Journal of Agricultural Research 43: 241-260.
- Skerman, P.J. & Riveros, F., 1990. Tropical grasses. FAO, Rome. pp. 721-724.
- Tothill, J.C. & Hacker J.B., 1983. The grasses of southern Queensland. University of Queensland Press, Brisbane [as T. australis]. pp. 402-404.
Authors
J.C. Tothill
