Brachiaria decumbens


Scientific name

Synonyms

Urochloa decumbens (Stapf) R.D. Webster

Family/tribe

Family: Poaceae (alt. Gramineae) subfamily: Panicoideae tribe: Paniceae.

Common names

signal grass (Australia);  Surinam grass , Surinamgras (German);  Australiano, braquiária, braquiária comum,  braquiária de alho, capim braquiária, decumbens (Portuguese – Brazil);  braquiaria, pasto alambre, zacate Surinam, pasto chontalpo, pasto de la palizada, pasto de las orillas, pasto peludo, pasto prodigio, zacate prodigio, pasto señal, señal, zacate señal, zacate signal (Spanish).

Morphological description

Low-growing, erect or decumbent, rhizomatous and stoloniferous perennial with bright green, moderately hairy leaves 7–20 mm wide and 5–25 cm long.  Leaves arise from trailing stolons that root at the nodes.  Leaf blades lanceolate .  Typical ‘signal’ seed head with 2–7 racemes, 1–5 cm long, borne on an axis up to 10 cm long.  Racemes almost at right-angles to the axis.  Elliptical spikelets, 4–5 mm long, borne in 2 rows on flattened (winged) rachis.  (In comparison, spikelets are borne in single rows for B. brizantha ).  Seed weight is 280,000/kg.
B. decumbens intergrades with B. brizantha and the species may be difficult to distinguish.  The main difference is in growth habit with B. brizantha more tufted and B. decumbens more decumbent and forming a denser cover.  The two are distinguished morphologically by the shape of the rachis, which is crescent-shaped in B. brizantha , and the arrangement and texture of spikelets.

Distribution

Native to:
Africa:  Central and East Africa from 500–2,300 m asl , including Burundi, Kenya, Rwanda, Tanzania, Uganda and Zaire.

Now widely distributed throughout tropical America, south-east Asia and the Pacific.

Cultivar Basilisk has been the most widely planted grass in South America.  Recent opinion is that ‘Basilisk’ is actually B. brizantha (see section on “Cultivars” for details).

Uses/applications

Mainly planted for permanent pastures, but also grown as fresh feed and for conservation under cut-and-carry systems by small- holders.  It has been planted as grazed ground cover in plantations and gives good cover for erosion control on hillsides.  Used in upland rice (Oryza sativa) systems in the Colombian savannas.  Can provide dense pasture cover for the control of Chromolaena odorata in China.

Ecology

Soil requirements

Grows on a wide range of soil types including those of low fertility, low pH (as low as pH 3.5) and high Al saturation.  Also moderately tolerant of Mn.  B. decumbens is much more tolerant of high Al than B. ruziziensis as it can detoxify Al in the root system by chelation with citrate and malate.  It does not respond to lime when grown on acid soils.
The root system of B. decumbens has finer and longer roots than some other Brachiaria species providing superior uptake of P and N from the soil.  However, it is less frequently grown on heavy clays subject to waterlogging , where it will not persist.

Moisture

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Grown in the humid tropics and warmer subtropics with rainfall generally 1,000–3,000 mm AAR (preferably >1,500 mm) but with a dry season up to 5 months.  In Ecuador, the species dominates on volcanic soils below 450 m asl and with an annual rainfall of 3,000 mm.
Stays green well into the dry season (better than B. brizantha ).  It can tolerate some short-term flooding but not temporary waterlogging (where B. humidicola is superior).

Temperature

Despite being native to the upland tropics, B. decumbens is most productive in the lowland humid tropics, or during summer in the subtropics or at higher altitudes.  Prefers temperatures above 19ºC.  Leaves are burnt off by light frost but the plants recover.

Light

Intermediate tolerance to shade and suitable for ground cover under more open plantations.  Common species under mature coconuts (>60% light transmission), but less tolerant of heavy grazing under reduced light than in full sun.

Reproductive development

Tetraploid aposporous apomictDiploid sexual biotypes are known, but have no commercial value.  Probably day-neutral in photoperiod response.

Defoliation

Very tolerant of heavy grazing.  The leaf area recedes showing some bare soil under lower rainfall conditions but the stolons persist.  Shading reduces tolerance of heavy grazing.  Persistent under regular cutting, but very frequent cutting results in prostrate leaf growth which is difficult to harvest.

Fire

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Usually not subjected to regular burning because leaf is normally heavily grazed or harvested before fires occur.  However, B. decumbens can be burnt during the dry season and recovers rapidly from stolons and seed with the onset of rains.

Agronomy

Establishment

Large areas are easily planted with the large, free-flowing seed. Seed is frequently dormant for 6 months after harvest and should be stored or scarified before planting.  Seed is broadcast at a rate of 2–4 kg/ha, then lightly harrowed and rolled.  Commonly planted with a range of forage legumes.
Can also be planted easily from vegetative sets (leaf with rhizomes) although it does not spread and cover new land as quickly as B. humidicola .

Fertiliser

Tolerant of low fertility but responds strongly to N and P fertiliser.  Animal production declines after a few years on acid soils cleared from rainforest unless maintenance fertiliser is applied every 2–3 years.
In Brazil, it is estimated that 40% of plant N comes from associated N-fixation under natural conditions, although the processes by which this occurs are not well understood.

Compatibility (with other species)

Good ground cover, aggressive growth and decumbent habit result in poor compatibility with broadleaf species.  Under lower defoliation pressure and on more fertile soils, B. decumbens can form a mono-specific sward .  Under heavier grazing with lower soil nitrogen but added phosphorus, B. decumbens can combine well with creeping legumes.

Companion species

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Legumes:  Desmodium heterophyllum , D. heterocarpon subsp. ovalifolium, Arachis spp., Stylosanthes guianensis var. guianensis, Centrosema molle , C. macrocarpum , Desmodium intortum .
On sandy soils in Colombian, Venezuelan and Brazilian savannas, Stylosanthes capitata .  Under higher rainfall and heavy grazing, Pueraria phaseoloides .  On very acid, sandy soils in Guyana, a number of small, native Desmodium species.

Pests and diseases

Relatively free from diseases and pests including leaf-cutting ants but susceptible to spittlebugs (Aeneolamia, Deois and Zulia spp.).  Spittlebug susceptibility has greatly reduced the use of signal grass in tropical America, although mature stands may recover from attack.  Some susceptibility to rust (Uromyces setariae-italicae).

Ability to spread

Spreads well and covers soil rapidly.  Has become naturalised in large areas of the neo-tropical lowlands.

Weed potential

Has become an environmental weed by vigorously colonising disturbed environments.

Feeding value

Nutritive value

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Moderately high (similar to other tropical grasses) but greatly dependant on the fertility status of the soil.  Intermediate to high digestibility (50–80%), chemical composition and intake.  CP ranges from 9–20% depending on soil fertility and management, but can decline rapidly with age of leaf, from 10% at 30 days to 5% at 90 days.
The inclusion of the legume D. heterocarpon subsp. ovalifolium increased the nitrogen concentration of the grass and the total N yield equivalent to 200 kg/ha N but the legume’s low palatability meant that little legume was eaten.

Palatability/acceptability

Moderately good but greatly depending on the fertility status of the soil.  Rejected by equines.  Livestock reject frosted grass .

Toxicity

Young cattle, sheep and goats can develop hepatogenous photosensitization although prevalence appears to be strongly related to environment.  For example, it is of major concern in Brazil and Papua New Guinea but is unheard of in Vanuatu and rare in Australia.  Transferring stock to pasture of different species can alleviate symptoms.  Photosensitization in bovines can be avoided by a rotation of 2 weeks on and 2 weeks off the grass .
Sporadic outbreaks have been related to mycotoxins from the saprophytic fungus Pithomyces chartarum, but also to saponins.

Production potential

Dry matter

DM yields can be very high under heavy fertiliser application, with yields of 10 t/ha/yr DM commonly recorded, possibly up to 30 t/ha under ideal conditions.  Production reduces dramatically in the dry season and will cease in winter in subtropical environments.
On fertile soils in humid-tropical Vanuatu, it produced 29 t/ha/year DM in the first year of growth, but only 16 t/ha/year as fertility declined in the second year of growth.  At high latitudes in Paraguay, yields were 14 t/ha/year.

Animal production

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Heavily fertilised pastures can be highly productive (up to 1,300 kg/ha liveweight gain) due to the high yields of herbage and ability to carry high stocking rates.  In humid-tropical Queensland, signal grass pastures fertilised with 336 kg/ha N and grazed at 7.7 head/ha produced 1,290 kg of liveweight gain.
In Brazilian savannas, at stocking rates of 2.5 head/ha, 340 kg/ha/yr LWG have been recorded.  In the humid tropics of Peru, at 4 head/ha, B. decumbens with D. heterocarpon subsp. ovalifolium gave LWGs of 380 g/hd/day and 640 kg/ha/yr.
On more fertile soils with a reasonable legume component, gains of 450–600 g/head/day for individual cattle and 400–600 kg/ha/yr are commonly achieved.

Genetics/breeding

Obligate apomict and tetraploid but some diploid accessions may show isoenzyme polymorphism.  Cross pollination can produce a (sterile) triploid hybridChromosome number 2n = 18, 2n = 4x = 36.

Seed production

B. decumbens seed in Australia and Brazil can be produced by direct heading with high-capacity harvesters capable of handling the large bulk of decumbent leaves which hold fallen seed.  At 16°S in Brazil, seed can be harvested 35–44 days after flowering, with 2 harvests per year (early and late in the wet season).  High seed yields of 400–1,000 kg/ha are common in Brazil and Australia, but seed yields are commonly poor at latitudes close to the equator.
Seed has a high percentage of dormancy following harvest.  Primary dormancy is physiological, whilst long-term dormancy is mechanical, caused by a restriction of the seed coat.  Dormancy may be broken by 6–9 months storage or by acid scarification .

Herbicide effects

Tolerates pre-emergence application of atrazine when establishing in weedy cultivation land.

Strengths

  • High productivity under intensive management.
  • Withstands heavy grazing.
  • Persists on low fertility, acid soils.
  • Good seed yields and therefore relatively low cost seed.

Limitations

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  • Susceptible to spittlebug attack in the New World tropics.
  • Poor compatibility with many legumes.
  • Low tolerance of poor drainage.
  • Photosensitization in sheep and goats.

Other comments

  

Selected references

CIAT (1992). Pastures for the Tropical Lowlands . CIAT, Cali, Colombia.
Lenné, J.M. and Trutmann, P. (eds) (1994) Diseases of Tropical Pasture Plants . CABI, Wallingford, UK.
Miles, J.W., Maass, B.L. and do Valle, C.B. (eds) (1996) Brachiaria : Biology, Agronomy and Improvement. Joint publication by CIAT, Cali, Colombia and Embrapa/CNPGC, Campo Grande, MS, Brazil.
Peters, M., Franco, L.H., Schmidt, A. and Hincapié, B. (2003) Especies forrajeras multipropÓsito: Opciones para productores de Centroamérica. CIAT Publication No. 333. CIAT, Cali, Colombia.
Schultze-Kraft, R. and Teitzel, J.K. (1992) Brachiaria decumbens Stapf. In: 't Mannetje, L. and Jones, R.M. (eds) Plant Resources of South-East Asia No. 4. Forages. pp. 58-59. (Pudoc Scientific Publishers, Wageningen, the Netherlands).
Thomas, D. and Grof, B. (1986) Some pasture species for the tropical savannas of South America. III. Andropogon gayanus , Brachiaria species and Panicum maximum . Herbage Abstracts, 56, 557–565.

Internet links

Cultivars

Cultivars

Country/date released

Details

Widely known as a cultivar of B. decumbens , cv. Basilisk was recently reassessed as B. brizantha based on rachis shape, and spikelet arrangement and texture.
‘Basilisk’
‘Brachiaria’
‘Señal’
‘Chontalpo’
‘Barrera’
‘Peludo’
(CPI 1694, CIAT 606,
BRA001058, ILCA 10871)
Australia (1966)
Cuba (1986/87)
Panama (1986)
Mexico (1989)
Venezuela (1989)
Costa Rica (1991)
Collected in open grasslands of the Great Lakes Plateau in Uganda.  Introduced into Australia in 1930 and selected for its very high DM yields in trials at South Johnstone during 1956–66.

Promising accessions

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Promising accessions

Country

Details

None reported.