Centrosema macrocarpum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Centrosema macrocarpum Benth.

Protologue: Ann. Nat. Hist. (Paris) 3: 436 (1839).

Family: Leguminosae

Chromosome number: 2n= 22, 20

Centrosema lisboae Ducke (1922).

C. macrocarpum is of tropical American origin, and occurs naturally between latitudes 20°S and 20°N; it is particularly frequent north of the equator where it extends from the extreme north of Brazil to Venezuela, Colombia and all Central American countries north to Mexico. Experimental lines have spread to many tropical countries for testing, including in South-East Asia.

The main use of C. macrocarpum is as a forage for ruminants. In pasture systems it can be grazed in pure legume stands ("protein bank") or in a mixture with grass. It is suitable for cut-and-carry systems and can also be used as ground cover in plantation agriculture.

C. macrocarpum provides a palatable, high-quality forage. Depending on plant age and soil fertility, N concentration in leaves ranges from 3.5-5.0% and in vitro DM digestibility from 45-70%; P concentrations are about 0.20%. There are 15-25 seeds/g.

A robust perennial, taprooted vine, prostrate in absence of a support; trailing stems with variable tendency to root at nodes. Stem pilose with greyish hairs when young, glabrescent, lignified at base. Leaves trifoliolate; stipules triangular, petioles and petiolules pubescent; leaflets broadly to narrowly ovate, apically acute to acuminate, rounded or slightly wedge-shaped at the base; central leaflet larger and longer petiolated than laterals, mostly 8-13 cm × 3-8 cm, papyraceous to subcoriaceous, almost glabrous to pubescent on lower or both surfaces; frequently with a light-green marking along midrib. Inflorescence an axillary raceme with up to 30 flowers inserted in pairs along rachis; flower papilionaceous, subtended by a pair of ovate-lanceolate-falcate bracteoles; calyx campanulate, 5-teethed with carinal tooth considerably longer than others; petals showy and cream-coloured with purple centre; standard orbicular-emarginate, 3-6 cm in diameter, pubescent outside; wings and keel much smaller than standard, directed upwards. Pod linear, compressed, up to 30 cm × 1 cm, straight to slightly bent and beaked, subglabrous, containing up to 25 seeds, dehiscent. Seeds transversely oblong to rectangular, on average 5 mm × 3 mm, yellowish-brownish unicoloured, mottled or marbled.

C. macrocarpum is extremely photoperiod-sensitive. Even as close as 3°to the equator, flowering is induced by shortening of daylength. Further conditions which promote flowering are the removal of accumulated biomass and the provision of support for plants to climb up.

Tripping of flowers, usually by large insects such as bumblebees, is required for seed-setting. The legume has specific Bradyrhizobium strain requirements.

There are several groups of distinct C. macrocarpum forms related to their geographical origin. Of these, the low-altitude ecotypes from northern South America (Colombia, Venezuela) are particularly promising as forage plants. As yet, no cultivar has been released. C. macrocarpum has occasionally been confounded with C. grandiflorum Benth.

C. macrocarpum is best adapted to the humid and sub-humid tropics with annual rainfall above 1000 mm. Once established, it is very drought-tolerant and can remain green during dry seasons as long as 3-4 months. It tolerates moderate shade. The legume grows well on a range of soils, provided they are well drained, but preferably on medium-textured soils. It has good tolerance of soil acidity including Al and Mn toxicity, and of low available P.

C. macrocarpum seed is drilled in rows or broadcast, alone or simultaneously with a grass, or strip-sown into an existing grass sward, at a rate of 3-5 kg/ha. In order to break hardseededness, mechanical or acid-scarification of seed is necessary. As it has specific Bradyrhizobium requirements, seed must be inoculated with an appropriate strain if the legume is to be established where it has not been sown before. Grasses suitable for association with C. macrocarpum are bunch grasses such as gamba grass ( Andropogon gayanus Kunth) and guinea grass ( Panicum maximum Jacq.); however, successful associations have also been obtained with the stoloniferous Brachiaria dictyoneura (Fig. & De Not.) Stapf.

Fertilization with P and K enhances establishment of C. macrocarpum on most tropical soils. Despite the legume's adaptation to moderately fertile to infertile soils, it responds well to maintenance fertilization with these nutrients.

When used in grazed pastures, legume persistence will be enhanced if C. macrocarpum is allowed to establish well before it is first grazed and if stocking rates are not excessive.

C. macrocarpum is one of the Centrosema species most tolerant of diseases and pests. None of the economically important diseases of the genus ( Rhizoctonia foliar blight, anthracnose, Cercospora leaf-spot, and bacterial blight) has been observed to affect C. macrocarpum seriously. Leaf-eating insects can be a problem during dry periods.

The legume is usually grazed or is consumed as fresh material after mowing. When mown, cutting intervals will depend on soil moisture and fertility; 10-14 weeks is suggested as an adequate interval with a cutting height of 10-15 cm.

Depending on soil-moisture conditions, DM yields on acid, moderately fertile to infertile soils range from less than 1 t to almost 5 t/ha per 12 weeks; annual DM yields in Colombia, at a site with bimodal rainfall distribution and a highly Al-saturated ultisol, averaged 15 t/ha. Under optimum conditions seed production reaches 800 kg/ha.

Evidence of considerable outcrossing has been observed in C. macrocarpum. This is a consequence of the tripping of flowers by bumblebees which also transfer pollen. Because of the large degree of outcrossing, plant populations within a given ecotype can show considerable variation. The species is well represented in the collection held by CIAT (Colombia) where a large number of quite variable accessions are available. A breeding project aimed at introducing the acid-soil tolerance of C. macrocarpum into C. pubescens Benth. is presently being concluded in Brazil.

Because of its adaptation to acid, infertile soils and drought, and its high productivity and nutritive value and good disease tolerance, C. macrocarpum is a valuable legume for the humid and sub-humid tropics. Its potential seems to be greater in cut-and-carry systems and for protein banks than as a component in a grass-legume pasture, where it is sensitive to grazing mismanagement.

• Keller-Grein, G. (Editor), 1990. Red Internacional de Evaluación de Pastos Tropicales, RIEPT-Amazonia. I Reunión-Lima, Peru, 6-9 Noviembre 1990. Documento de Trabajo No 75. CIAT, Cali, Columbia. 2 Vols. 1119 pp.
• Schultze-Kraft, R., 1986. Natural distribution and germplasm collection of the tropical pasture legume Centrosema macrocarpum Benth. Angewandte Botanik 60: 407-419.
• Schultze-Kraft, R. & Clements, R.J. (Editors), 1990. Centrosema: biology, agronomy, and utilization. CIAT, Cali, Colombia. 667 pp.

R. Schultze-Kraft