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Signal grass (Brachiaria decumbens)

IMPORTANT INFORMATION: This datasheet is pending revision and updating; its contents are currently derived from FAO's Animal Feed Resources Information System (1991-2002) and from Bo Göhl's Tropical Feeds (1976-1982).

Datasheet

Description
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Common names 

Signal grass, signalgrass, sheep grass, Kenya sheep grass, Suriname grass [English]; braquiaria, decumbens, pasto alambre, pasto braquiaria, pasto chontalpo, pasto de la palizada, pasto de las orillas, pasto peludo, pasto prodigio, zacate prodigio [Spanish]; Australiano, braquiária, braquiária comum, braquiária de alho, capim braquiária, decumbens [Portuguese]; ya siknaentonnon, ya surinam [Thai] (Miles et al., 1996)

Synonyms 

Urochloa decumbens (Stapf) R. D. Webster, Brachiaria bequaertii Robyns, Brachiaria brizantha sensu Senaratna, Brachiaria eminii (Mez) Robyns, Panicum eminii Mez, Urochloa eminii (Mez) Davidse.

Taxonomic information 

Many Brachiaria species, including Bracharia decumbens, have been placed by some authors in the Urochloa genus, so the taxon Urochloa decumbens is often considered as the correct one. However, these changes remain disputed and many recent papers still refer to Bracharia decumbens (Torres González et al., 2005).

Description 

Morphological description

Signal grass (Brachiaria decumbens Stapf or Urochloa decumbens (Stapf) R. D. Webster) is a high-yielding, vigorous rhizomatous and stoloniferous, medium-lived (5 years) perennial grass. It has a dense root-system with many bunched, quickly growing roots that go as deep as 2 m in the soil layers (Husson et al., 2008). Signal grass has a prostrate or decumbent habit, up to 60 cm high. Its flowering stems can however be up to 100 cm in height, arising from the stolons (Cook et al., 2005; Loch, 1977). Signal grass roots from the nodes of the stolons. The leaves are short, hairy and bright green in colour (Cook et al., 2005; Bogdan, 1977). Leaf-blades are lanceolate, 10-14 (-25) cm long x 8-10 (-12) mm wide (Husson et al., 2008; Cook et al., 2005; Bogdan, 1977). The inflorescence is a panicle with 2-7 slightly curved, 2-5 cm long racemes. The racemes are almost at right-angles to the 10-20 cm long axis (Husson et al., 2008; Cook et al., 2005). The spikelets are hairy, 4-5 mm long and borne in 2 rows along the rachis (Cook et al., 2005; Loch, 1977). 1 000 seeds weigh 3.6 g (Husson et al., 2008)

Brachiaria decumbens and Brachiaria brizantha are very similar morphologically, which has led to incorrect identifications (Miles et al., 1996). It mainly differs in its habit which is more decumbent, less tufted and forms a looser cover (FAO, 2016; Cook et al., 2005; Schultze-Kraft et al., 1992). Brachiaria decumbens cv. Basilisk originally identified as Brachiaria decumbens, was reidentified as Brachiaria brizantha (FAO, 2016). 

Utilization

Brachiaria decumbens is the most cultivated species of the genus Brachiaria. Unlike Congo grass (Brachiaria ruziziensis), it has no or very few diseases, the only issue might be due to spittlebug (Loch, 1977). It is a valuable forage used in permanent pastures. It is a high-yielding forage that forms low leafy stands and does well on infertile soils. It is palatable to all classes of livestock and withstands heavy grazing (Cook et al., 2005; Loch, 1977). Signal grass can be grazed, cut to be fed fresh or to be made into hay. Signal grass is also used as a cover crop to prevent erosion and to control weeds and insects (Mollot et al., 2012; Cook et al., 2005).

Distribution 

Signal grass originated from the highlands of central and eastern Africa (FAO, 2016; Cook et al., 2005). It is now widespread in the tropics and sub-tropics. It was introduced from Africa into sown pastures of humid lowlands of tropical America in the 50-60's (Pizarro et al., 1996). Signal grass has also been widely naturalized in South-Est Asia and in the Pacific region (Schultze-Kraft et al., 1992).

Signal grass is naturally found in open grasslands or in partially shaded areas, between 27°N and 27°S, from sea level up to an altitude of 1750 m. It grows in frost-free areas with temperatures over 19°C. Optimal growth occurs between 30-35°C (FAO, 2016) and in places where average rainfall is over 1500 mm. Signal grass has a deep root system which effectively extracts P and N from the soil; it can grow on a wide range of soils including low fertile soils with low pH (down to 3.5) and high Al concentration (it does better than B. brizantha in such conditions). Signal grass is also moderately tolerant of Mn. However, unlike Rhodes grass and many other perennial grasses, signal grass is sensitive to salinity (Deifel et al., 2006). It does not well on heavy clays subject to waterlogging but is tolerant of a dry season of 4 or 5 months (FAO, 2016). Signal grass remains productive late in the dry season and for this reason compares favourably to Pangola grass (Digitaria decumbens), Guinea grass (Megathyrsus maximus) or Para grass (Brachiaria mutica) (FAO, 2016). Signal grass is tolerant of shade and can be intercropped with tall species and in tree plantations (rubber, banana, coconut). However it is less tolerant of heavy grazing under reduced light (Cook et al., 2005). Though not really subject to fire, signal grass can be burnt and resume its growth from stolons and seeds with the onset of rains (Cook et al., 2005).

Forage management 

Management

Signal grass can be propagated by seeds or by vegetative cuts (leaf and rhizomes). Scarified seeds can be broadcasted on a well prepared seed-bed with companion legumes such as stylo (Stylosanthes guianensis), centro (Centrosema pubescens) or puero (Pueraria phaseoloides) which will be outcompeted after a few months because of signal grass pioneering habit (FAO, 2016). Hetero (Desmodium heterophyllum) appeared to do better as a companion legume (Cook et al., 2005).

In N deficient pastures, signal grass and B. humidicola can be associated to adapted legumes (Pizarro, 2001). In Fiji, pinto peanut (Arachis pintoi) formed stable mixtures with signal grass. Similarly, in Indonesia signal grass combined successfully with Arachis glabrata (Stür et al., 1996).

Signal grass requires no more than 3 months to form a dense cover. Then it should be heavily and frequently grazed to maintain leaf growth. Signal grass withstands trampling. Rotational grazing was recommended and stocking rates up to 10 heads/ha could be reached before the signal gras stand collapsed (Fisher et al., 1996).

Yield

Signal grass is a high yielding species particularly if N fertilizer is provided. Up to 30 tons DM/ha could be obtained on fertiles soils of Vanuatu and the same biomass production could be obtained under coconut plantations, in Solomon islands (Cook et al., 2005). The average yield is however generally lower with about 10 tons DM/ha. Signal grass yielded 4 tons DM/ha without fertilizer in Colombia (FAO, 2016). Production occurs between spring and autumn, is reduced during dry seasons and null during winter in subtropical environments (Cook et al., 2005).

Environmental impact 

Cover crop et soil reclamation

Signal grass provides a good ground cover, improves fertility as well as soil structure in banana plantations and in many other environments (Vézina, 2015; Boddey et al., 1996). Signal grass deep and dense root system prevents soil erosion, it facilitates water infiltration, decreases leaching of soluble nutrients and sequesters high amounts of C in the soil (358 tons C/ha) (Saraiva et al., 2014; Boddey et al., 1996). It was also reported to be a valuable cover crop in upland rice systems. Growing signal grass before rice produced higher rice grain yield with application of Ammonium sulfate and nitrification inhibitor (Rosolem et al., 2005). It was successfully used in tomato no-tillage systems to reduce weeds and improve soil structure (Silva Hirata et al., 2009).

Signal grass could be used for reclamation of sites contaminated with lead, nearby highways and urban areas where Pb contamination is likely to have occurred. Signal grass has been found considerably more tolerant to Pb than Rhodes grass (Chloris gayana), resulting in a 50% reduction of Pb (Kopittke et al., 2007).

Weed potential and weed controller

It was shown that germinating seeds and leachates of green parts of signal grass had allelopathic effects on Phalaris canariensis, Lactuca sativa (standard species) and Melinis minutiflora. This could enhance its invasive potential in the Cerrados of Brazil (Barbosa et al., 2008).

In China, it is used to make dense pasture cover for the control of the invasive and poisonous Chromolaena odorata (Wu et al., 1991 cited by Cook et al., 2005). Among treatments, digging out of Chromolaena followed by burning and planting with signal grass was the most effective (Rusdy et al., 2013).

Insect control

In banana agroecosystems of the french West Indies, signal grass as a cover crop is increasingly used to control weeds and to improve physical soil properties (Mollot et al., 2014). In these agroecosystems, it was shown that signal grass could enhance the number of Solenopsis geminata, a predator of the banana weevil (Cosmopolitus sordidus) and thus contributes to control this pest (Mollot et al., 2012).

Nutritional aspects
Potential constraints 

Hepatogenous photosensitization

A widespread sporadic toxicity syndrome associated with Brachiaria species is hepatogenous photosensitization. Sheep, goats and cattle develop skin lesions, facial edema, liver damage and ruminal stasis that result in severe drops in weight gain (down to 40%) and even in death (in 17% of cases) if the animals are not removed from the pasture (Fagliari et al., 2003). The disease occurs within the first 30 days after grazing signal grass or until 60 to 90 days after. The poisoning may affect cattle, sheep, goats and buffalo. However, sheep are more susceptible than other species, and especially lambs are more susceptible than adults. Differences of susceptibility existing among animals might be genetically inherited (Riet-Correa et al., 2011).

Hepatogenous photosensitization syndrome has been reported in ruminants grazing Brachiaria decumbens in Africa, Southeast Asia and South America (FAO, 2010; Lascano et al., 1996). The cause of toxicity would be the presence, in bile ducts and hepatocytes, of crystals of insoluble salts of sapogenin glucuronides originating from steroidal saponins present in signal grass. Sapogenin content can vary in the same Brachiaria species due to environmental stress, plant age and developmental stage.

Outbreaks of Brachiaria spp. poisoning in central western Brazil are frequently observed in pastures left ungrazed during more than 30 days. They also occur during the growing stage of the pastures at the onset of the rainy season (Brum et al., 2009).

Some buffalo and sheep might be resilient to hepatogenous photosensitization. These poisoned animals showed histologic lesions and GGT serum concentrations but no clinical signs of disease. Selection of resistant or resilient animals and breeding of varieties with low saponin content could prevent poisoning (Riet-Correa et al., 2011).

Ruminants 

Readily grazed.

Rabbits 

Fresh

Green Brachiaria decumbens has a medium palatability for rabbits, and when mixed at 50:50 with a legume forage, the total daily DM intake depends on the legume associated, Lablab purpureus or Centrosema pascuorum (Iyeghe-Erakpotobor et al., 2008).

Bracharia decumbens is a grass effectively used as green forage in small scale rabbit systems in Uganda (Lukefahr, 1998) or in Indonesia (Sudaryanto et al., 1984; Maskana et al., 1990). As forage it is mainly a source of fibre, in relation with its low protein level (about 7-10%) and the very high NDF content (60-70%). In addition, the very low calcium level (less than 4 g/kg for a recommendation of 11-12 g/kg) and secondarily the low phosphorus content, make questionable its use for lactating rabbit does if an additional calcium source is not simultaneously provided (Lebas, 2004).

Hay

In Nigeria, B. decumbens hay is considered a reference forage distributed ad libitum or in limited quantity together with various concentrate diets, for growing rabbits as for breeding does (Iyeghe-Erakpotobor et al., 2005; Iyeghe-Erakpotobor et al., 2006). As complement of classical rabbit concentrate, it represents about one third of the total daily dry matter intake of growing rabbits when offered ad libitum (Iyeghe-Erakpotobor et al., 2006). If Brachiaria decumbens hay is included in a complete balanced diet after grinding, the incorporation level may be up to 15-20% without problem. For such an incorporation, a calculated digestible energy content of 8.5 MJ/kg DM and a calculated digestibility coefficient of 54-55% for crude protein could be proposed (Lebas, 2013) in absence of any in vivo determination.

Nutritional tables
Tables of chemical composition and nutritional value 

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used

IMPORTANT INFORMATION: This datasheet is pending revision and updating; its contents are currently derived from FAO's Animal Feed Resources Information System (1991-2002) and from Bo Göhl's Tropical Feeds (1976-1982).

Main analysis Unit Avg SD Min Max Nb
Dry matter % as fed 25.7 5.3 19.5 39.6 29
Crude protein % DM 8.2 3.5 1.9 14.1 53
Crude fibre % DM 31.2 5.4 22.6 39.7 40
NDF % DM 68.3 5.9 57.8 75.8 11 *
ADF % DM 36.9 4.6 30.1 45.7 22 *
Lignin % DM 5.0 1.2 3.6 7.8 13 *
Ether extract % DM 2.3 0.6 1.4 2.9 8
Ash % DM 8.7 1.8 5.4 12.2 52
Gross energy MJ/kg DM 18.1 2.8 15.4 20.5 3 *
 
Minerals Unit Avg SD Min Max Nb
Calcium g/kg DM 3.9 1.1 1.9 6.1 36
Phosphorus g/kg DM 2.3 1.2 0.6 4.4 36
Potassium g/kg DM 17.8 8.5 2.4 29.8 32
Sodium g/kg DM 0.5 0.4 0.6 2
Magnesium g/kg DM 2.1 0.6 1.4 3.8 36
Manganese mg/kg DM 148 65 83 281 9
Zinc mg/kg DM 30 17 10 76 11
Copper mg/kg DM 4 3 2 11 11
Iron mg/kg DM 707 140 1273 2
 
Ruminant nutritive values Unit Avg SD Min Max Nb
OM digestibility, Ruminant % 54.0 3.8 54.0 68.0 8 *
Energy digestibility, ruminants % 51.6 51.6 62.9 2 *
DE ruminants MJ/kg DM 9.3 9.3 12.9 2 *
ME ruminants MJ/kg DM 7.6 *
ME ruminants (gas production) MJ/kg DM 6.6 0.2 6.3 6.8 4
Nitrogen digestibility, ruminants % 58.9 13.2 33.5 71.0 8

The asterisk * indicates that the average value was obtained by an equation.

References

Abaunza et al., 1991; Aregheore et al., 2006; Aumont et al., 1991; Butterworth, 1963; CGIAR, 2009; CIRAD, 1991; Dougall et al., 1958; Evitayani et al., 2004; Evitayani et al., 2004; Gowda et al., 2004; Nasrullah et al., 2003; Xandé et al., 1989

Last updated on 27/11/2012 14:27:53

References
References 
Datasheet citation 

DATASHEET UNDER CONSTRUCTION. DO NOT QUOTE. http://www.feedipedia.org/node/489 Last updated on August 23, 2016, 13:12

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