Centrosema pascuorum Mart. ex Benth.
Common names and cultivars:
Common name (Australia): Centurion, Centro
Cultivars (Australia): Two cultivars were released in Australia, cvv. Cavalcade and Bundey (Oram, 1990). Cv. Bundey is differentiated from cv. Cavalcade by smaller seeds, and hairy stems and petioles (Partridge, 2003).
Centrosema belongs to the tribe Phaseoleae of the subfamily Papilionoideae. Together with the closely related C. arenicola and C. virginianum, C. pascuorum forms the Centrosema species group 2 (Williams and Clements, 1990). Taxonomic information is also available in Barbosa-Fevereiro (1977). The chromosome number of C. pascuorum is 2n = 22 (Clements, 1992).
In 1988, the world collection of C. pascuorum germplasm comprised 95 accessions with significant collections held by CIAT (Centro Internacional de Agricultura Tropical, Cali, Colombia) and the former Australian Tropical Forage Genetic Resource Centre (ATFGRC) of CSIRO (Schultze-Kraft et al., 1989). Passport data of the germplasm can be accessed on the Internet (http://singer.cgiar.org/). According to a comprehensive evaluation of the collection carried out by Thomson et al. (1997), there is large variation in herbage and seed yields. In general, the most vigorous accessions are late flowering lines collected in northeastern Brazil; otherwise accessions from Brazil are the most diverse. Accessions from Central America are early flowering, with high levels of hard seed; Venezuelan accessions are characterized by small, mottled seeds - in contrast to the common greenish-yellow to brown seed colour of the Brazilian germplasm - and are early to mid season flowering. There is also considerable variation in flowering time, seed size and hardseededness (Thomson et al., 1997).
Centrosema pascuorum is an annual, twining herb that can root from the nodes of trailing stems under moist conditions. Stems are cylindrical, glabrous or scarcely pilose, extending up to 2 m from the crown. Leaves are trifoliolate, often held erect and paraheliotropic especially during dry periods. Petioles are 25-50 mm long, glabrous to scarcely pilose (Clements, 1992). Leaflets of the Australian cultivars are long (50-100 mm) and narrow (5-10 mm) (Partridge, 2003) and give a C. pascuorum sward, from some distance, a grass-like aspect; however, in the available collection there exists also great variation in leaflet shape (Thomson et al., 1997). Inflorescences are racemose; flowers are borne singly or in pairs at the end of a short peduncle. The corolla is wine red to crimson, 15-25 mm long and wide. Flowers are predominantly self-pollinated. Pods are linear to slightly curved, 4-8 cm long and 3-4 mm wide, laterally compressed with a dark longitudinal stripe. They weight of 21 g (48,000 seeds/kg) and cv. Bundey 17 g (58,000 seeds/kg) (Oram, 1990). Not much information is available on the photoperiod response of C. pascuorum but flowering time appears to be related to sites of origin (Clements and Williams, 1980; Clements, 1990) and cv. Cavalcade is known to be a short day plant (Clements, 1992).
Geographic distribution and adaptation
C. pascuorum is a tropical lowland species, found naturally at altitudes between 20 m and 1000 m. Its geographical distribution spans from almost 17° N in Mexico to almost 20° S in Brazil. Main areas of distribution are semi-arid Northeast Brazil, the Pantanal, coastal Ecuador, Northern Venezuela and Guyana, and Mesoamerica from Southern Mexico to Panama; most commonly it is found in Northeast Brazil and Venezuela. Annual rainfall at sites of origin is between 350 and 1500 mm (usually below 1000 mm), with 4-10 dry months. Soils at the collection sites are mostly of medium to high fertility (Schultze-Kraft et al., 1990; Thomson et al., 1997). Recently, a subtropical form was found in the Paraguayan Chaco (Schultze-Kraft, 1997).
C. pascuorum is adapted to tropical areas with a pronounced dry season of up to 8 months; 700 to 1500 mm/year rainfall is suitable. Though individual plants die off under drought conditions (Peters et al., 1994), populations persist through escape mechanisms such as annual life span, rapid growth and flowering, and high seed production. Morphologically, the narrow leaflets and phototropism (i.e. erect leaves oriented towards sunlight) are also adaptation mechanisms to drought (Clements et al., 1983; Clements, 1990); Ludlow et al. (1983) describe osmotic and stomatal adaptation mechanisms to drought.
C. pascuorum is tolerant to seasonal inundation, with better adaptation of later flowering accessions such as cv. Bundey (McCosker, 1987; Clements, 1990). The ability to compete with weeds and persistence of stands through seeds depends on plant vigour: If regrowth is weak, grasses tend to dominate the sward and have to be controlled actively (Anning, 1982; McCown et al., 1985; 1986; Clements et al., 1986; McCosker, 1987; Ross and Cameron, 1991).
C. pascuorum is adapted to a wide range of soils, from sand to heavy clay and from slightly acid to alkaline soils (pH 5-8.5) (Clements, 1992).
Cvv. Cavalcade and Bundey are fast growing cultivars adapted to areas with annual rainfall between 700 mm and 1500 mm, with a pronounced dry season. Both cultivars tolerate water logging and some flooding. Cv. Cavalcade is earlier flowering and better adapted to drier areas with short wet season (700 to 900 mm) while cv. Bundey is better suited to seasonal flooding and higher rainfall (1300 to 1500 mm). Under such conditions cv. Bundey stays green longer into the dry season than cv. Cavalcade (McCosker, 1987; Partridge, 2003).
Seed scarification (heat treatment or sulfuric acid) is advisable to reduce hardseededness. In soils without previous legume cultivation, C. pascuorum responds to inoculation with appropriate rhizobium (Sylvester-Bradley et al., 1990) and mycorrhiza (Saif, 1987).
Land preparation and sowing
Centrosema pascuorum is established by seed, at a seeding rate of 2-6 kg/ha (Clements, 1992; Cameron, 1996a; 1998). For seed production and hay crops of cv. Cavalcade in Australia, seeding rates up to 10-15 kg/ha are reported to ensure good plant stands. Some soil disturbance is crucial to ensure good establishment (Cameron, 1998). C. pascuorum is best sown, drilled or broadcast, in a cultivated seed bed at a depth of 1-2 cm. Best time for sowing is the start of the wet season. It is advisable to control weeds during establishment. Superphosphate fertilization will enhance establishment and growth. Depending on soil conditions, for establishment 100-250 kg/ha, for maintenance 50-100 kg are recommended (Cameron, 1996a; 1998).
Though correlation between flowering date and herbage yield is low, late flowering accessions from Brazil tend to be more productive. Accessions with high herbage yields also tend to have a higher ability to root at nodes of trailing stems (Thomson et al., 1997). C. pascuorum grows well on a wide range of soils including soils with low phosphorus content (McCosker, 1987; Salinas et al., 1990); however, very acid soils with a pH below 5 should be avoided (Clements et al., 1983; Schultze-Kraft and Keller-Grein, 1985; Kretschmer, 1989). The ability of C. pascuorum to maintain quality as standing hay are the subject of contrasting reports: while Peters et al. (1994) report rapid leaf loss of cv. Cavalcade after onset of the dry season in Northern Nigeria, according to Cameron (1996a, 1998) cvv. Bundey and Cavalcade retain leaves for 2 to 3 months into the dry season in the Northern Territory of Australia, allowing hay to be made.
Contrasting reports also exist for the persistence of cvv. Bundey and Cavalcade under grazing; the ability to drop seeds before grazing seems to be critical (Cameron, 1996a; 1998, Pengelly and Conway, 1998). Cvv. Bundey and Cavalcade mix well with grasses such as Cenchrus ciliaris, Urochloa mosambicensis, Andropogon gayanus, Brachiaria decumbens, Setaria sphacelata and Panicum maximum (Clements, 1992; Cameron, 1996a; 1998). For pure C. pascuorum stands, DM yields of 4-9 t/ha/year are reported (Clements, 1992).
C. pascuorum is suitable for mixtures with grasses, or in
pure stands for ley-farming (McCown et al., 1985; 1986); it
is an excellent hay (Clements, 1992). More recently farmers in Northern
Territory, Australia, are growing Cavalcade to produce legume cubes
(Thiagalingam et al., 1997). Hay giving yields of about 7 t/ha
is cut with a rotary head cutter and dried in the field to 10% moisture.
Bales are shredded and mixed with bentonite (a volcanic-ash clay material
containing Fe, Mg and either Na or Ca), sprayed with water to 12%
moisture and then cubed under very high pressure. In 1997, 8000 t
of Cavalcade cubes were produced in a year (Anonymous, 1997). C.
pascuorum stands persist through a seed bank. For hay production,
renovation every 3 or 4 years is recommended to maintain a pure stand
(Cameron, 1996a). In ley-farming, the C. pascuorum phase is
able to provide 80-100 kg nitrogen/ha to the system (Thiagalingam
et al., 1997).
Cv. Cavalcade is the result of an Australian breeding program (1976-1981) which aimed at the development of a cultivar with high forage and seed yields, and nematode resistance. (Clements et al., 1986; Stockwell et al., 1986).
Diseases and pests
A number of diseases and pests have been reported for C. pascuorum, however without causing major damages, e.g., Little Leaf Mycoplasma (Thomson et al., 1997), Centrosema Mosaic Virus (Morales, 1994) and other diseases such as Cercospora canescens (leafspot), Colletotrichum truncatum (anthracnose), Pseudocercospora bradburyae (leaf spot), Rhizoctonia solani (foliar blight) and Neocosmopora vasinfecta (Lenné, 1990; 1994; Clements, 1992), also sucking insects during seed production (Kretschmer et al., 1980; Clements, 1992). Susceptibility to root knot nematodes (Meloidogyne spp.) needs to be taken into account when C. pascuorum is to be used in rotation with crops. Pagria flea beetle (Pagria sp.) rarely cause severe damage in Northern Australia in both cvv. Bundey and Cavalcade (Cameron, 1996a; 1998).
C. pascuorum flowers 2 to 5 months after sowing. In the germplasm evaluation of Thomson et al. (1997), there was a negative correlation between seed yield and time to flowering but no consistent relationship between seed yield and seed size. For seed production well drained sandy loams are best suited. At least 5 kg/ha seed are sown, with fertilization according to soil properties: a general recommendation is 150 to 250 kg superphosphate/ha for establishment, and 100 to 150 kg superphosphate/ha and 50 to 100 kg muriate of potash/ha for maintenance. For reliable seed production cvv. Cavalcade and Bundey need rainfall of at least 1000 and 1100 mm, respectively. Seed is suction-harvested (slow and energy consuming), or stands are mown prior to pod shattering followed by use of conventional harvester (Cameron, 1996b). Seed yields of 250 to 1500 kg/ha are reported (Clements et al., 1983; Stockwell et al., 1986; Ferguson et al., 1990; Kachelriess, 1993; Cameron, 1996b).
Forage quality and animal production
C. pascuorum is a high quality forage with good palatability. Crude protein content and digestibility vary according to plant age and season from 6 to 27% and 42 to 79%, respectively (Lascano et al., 1990; Thiagalingam et al., 1997; Pholsen et al., 2000). Mineral contents are similar to C. pubescens (Clements et al., 1984). Not much published literature is available on animal production on C. pascuorum pastures. However, there are Australian reports of daily liveweight gains of 460-540 g/animal during the dry season and in three consecutive years of cattle on a Cavalcade ley pasture, in comparison with liveweight losses of 140-240 g/animal on native pasture (McCown et al., 1986). Also in semi-arid/dry-sub-humid Northern Territory (Australia), C. pascuorum remained the dominant pasture component after 5 years of stocking at 3.3 steers/ha, consistently producing dry-season liveweight gains of 20-50 kg/ha (Thiagalingam et al., 1997). Chansiri et al. (2001) report improved milk yield and quality when dairy cows in NE Thailand were fed Cavalcade roughage instead of urea treated rice straw.
Main attributes and shortcomings
C. pascuorum is a high-quality forage for pastures and ley-farming, and for production of hay and legume cubes. It is well adapted to the dry tropics, tolerates seasonal flooding and adapts to a wide range of soil conditions including heavy clays but excluding very acid, low-fertility soils. Being an annual, its persistence depends on an adequate soil seed reserve. For ley-farming, susceptibility to root-knot nematodes is a limitation.