Bothriochloa pertusa (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Bothriochloa pertusa (L.) A. Camus

Protologue: Ann. Soc. Linn. Lyon 76: 164 (1931).

Family: Gramineae

Chromosome number: 2n= 40 (tetraploid), 50 (pentaploid), 60 (hexaploid)

Synonyms

Holcus pertusus L. (1771), Andropogon pertusus (L.) Willd. (1806), Amphilophis pertusa (L.) Nash ex Stapf (1916).

Vernacular names

• Indian couch grass, Indian bluegrass, sweet pitted grass (En)
• Indonesia: suket putihan (Javanese), rebha las-alasan (Madura)
• Malaysia: rumput embun
• Philippines: salay-parang (Tagalog), salay (Pangasinan)
• Thailand: ya-hom (central), ya-hangma (northeast)
• Vietnam: huyêt tha'o lô.

Origin and geographic distribution

Indian couch grass is widely distributed in Asia from Arabia to South-East Asia, and is particularly prominent on the Indian subcontinent. It has been introduced to other tropical areas and is now naturalized in tropical America, Australia and on several island groups (e.g. Hawaii).

Uses

Indian couch grass is used mainly as a forage for ruminants, but also for soil conservation, revegetating mine sites, lining floodways, lawns, recreation areas and playing fields.

Properties

Chemical composition and nutritive value depend upon age and soil fertility. Young green leaves may contain more than 2% N and 0.2% P, and be 70% digestible. These values decrease with age and at the end of the wet season will be considerably lower. Indian couch grass develops a high stem to leaf ratio with age and this reduces both the quality and palatability of herbage. Standing forage in the dry season may contain only 0.5% N, 0.05% P and be 45% digestible. Indian couch grass is moderately palatable as cattle sometimes avoid eating it whilst other grasses are available. It has a strong odour when crushed.

There are 650-750 seeds/g.

Botany

A low growing, stoloniferous perennial of variable size and growth habit. Stolons root readily at the nodes and produce small tufts of leaves. Culms are smooth, erect or geniculately ascending, up to 60 cm tall and 3 mm in diameter; nodes are prominent and may be glabrous or covered with hairs up to 3 mm long. Leaf linear-acuminate, 5-10(-30) cm × 4-6 mm, bright to dark green, usually glabrous except for a few hairs up to 3 mm long especially in the throat; ligule a shallow membrane surrounded by long ciliate hairs. Inflorescence 3-6 cm long, subdigitate, bearing 3-13 racemes each 2-7 cm long; spikelets in alternate pairs, one sessile, one pedicelled, on a slender rachis; sessile spikelet with a short blunt ciliate-hairy callus, a lower glume with a circular depression (pit) in upper half and upper lemma with a kneed and twisted scaberulous awn 1.5 cm long; pedicelled spikelet usually neuter, pitless. Seed awned, with weak antrorse hairs.

Seeds germinate early in the wet season and vegetative growth continues until soil water is exhausted. Time of flowering varies widely between strains but may commence 3-4 weeks after the start of the wet season and continue until growth ceases. Seed matures in 3-4 weeks. The onset of flowering can be delayed by poor growing conditions and flowering is checked by frost.

B. pertusa is morphologically indistinguishable from the mainly African B. insculpta (A. Rich.) A. Camus, but they do not interbreed. B. pertusa is less robust, more stoloniferous, and bears fewer and shorter racemes. It is also closely related to B. decipiens (Hack.) C.E. Hubbard, B. longifolia (Hack.) Bor, B. panormitana (Parl.) Pilger and B. radicans (Lehm.) A. Camus.

Seed of naturalized strains (particularly Bowen strain) is available in northern Australia. Cultivars "Medway" and "Dawson" were released in Queensland in 1991. They are later flowering and leafier than the Bowen strain. "Dawson" is particularly useful as a lawn grass.

Ecology

Indian couch grass grows in tropical areas with warm season dominated rainfall of 500-1400 mm per year. It survives in areas which are subject to frost, although its vigour is reduced, as frost kills the plant tops leaving only the basal parts alive. Indian couch grass hays off rapidly when soil moisture becomes depleted but can withstand moderate drought. Prolonged drought or fire will substantially reduce the basal area of the stand, although regrowth is rapid when growing conditions become favourable. Indian couch grass is found on a wide range of soil types. It is most competitive on infertile to moderately fertile soils. Prolonged waterlogging will kill or reduce its basal area.

Agronomy

Indian couch grass can be established vegetatively from runners, but is normally established from seed. Freshly harvested seed is dormant, but dormancy breaks down after 4-8 months storage. It can be established under a variety of conditions, but best results are obtained by sowing on or near the soil surface of a well cultivated seed-bed during the early wet season. Some seed-harvesting ants remove the seed, so early sowing should be avoided where these are present. Seeding rate is 1-3 kg/ha.

Indian couch grass can be used by continuous or rotational grazing, or cutting. It will stand close defoliation and is most prominent in heavily grazed or closely mown areas. It is used in association with legumes, although some problems have been experienced as it may exclude Stylosanthes hamata (L.) Taub. and other low-growing legumes. Indian couch grass is usually grown without fertilizers. However, yields can be increased substantially by fertilization as it responds well to both N and P. There are no important diseases or pests although it is attacked by rust. Indian couch grass is harvested by grazing animals but can be made into hay. It produces 1-5 t/ha of dry matter depending on seasonal conditions, soil fertility and associated species.

Genetic resources and breeding

There is a wide variation in Indian couch grass in morphological, flowering and agronomic characteristics. Collections, mainly originating from India, are held by ATFGRC (CSIRO, Australia) and the Queensland Department of Primary Industries.

There are no breeding programmes and any improvement will depend on selection from naturally occurring populations. Important objectives for any selection process will be to increase herbage yield, quality and palatability whilst maintaining the adaptability to a range of environments, ability to provide effective soil cover, persistence under heavy grazing and colonizing ability.

Prospects

Indian couch grass is an effective colonizing grass which provides good ground cover, reasonable quality herbage, is tolerant of heavy grazing and suited to the drier regions of South-East Asia. It has no rhizomes and is easily killed by cultivation so is unlikely to become a weed in cropping areas.

Literature

• Bisset, W.J., 1980. Indian bluegrass has special uses. Queensland Agricultural Journal 106: 507-517.
• de Wet, J.M.J. & Higgins, M.L., 1963. Species relationships within the Bothriochloa pertusa complex. Fyton 20: 205-211.
• McIvor, J.G., 1984. Phosphorus requirements and responses of tropical pasture species: native and introduced grasses and introduced legumes. Australian Journal of Experimental Agriculture and Animal Husbandry 24: 571-578.
• Skerman, P.J. & Riveros, F., 1990. Tropical grasses. FAO, Rome. pp. 230-233.
• Truong, P.N. & McDowell, M., 1985. Indian bluegrass for soil conservation and land stabilization in Queensland. Journal of Soil Conservation Service of New South Wales 41: 38-44.

Authors

J.G. McIvor & S.M. Howden