Calopogonium mucunoides (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Calopogonium mucunoides Desv.

Protologue: Ann. Sci. Nat. Sér. 1, 9: 423 (1826).

Family: Leguminosae - Papilionoideae

Chromosome number: 2n= 36

Vernacular names

• Calopo (En)
• Indonesia: kacang asu (Javanese), kalopogonium (Indonesian)
• Philippines: santing (Sulu), karaparapak sara naw (Mar.)
• Thailand: thua-khalapo.

Origin and geographic distribution

Calopo is indigenous to tropical America and the West Indies. It was introduced into tropical Africa and Asia in the early 1900s and to Australia in the 1930s. Calopo was taken into use as a green manure and cover crop in Sumatra in 1922 and soon thereafter in the rubber and sisal plantations of the central and eastern parts of Java. It was then brought to Malaysia as a cover crop for rubber. Calopo became naturalized in Indonesia and Malaysia, and has spread to most humid tropical areas of the world.

Uses

Calopo is well recognized as being a valuable pioneer legume to protect the soil surface, reduce soil temperature, fix atmospheric nitrogen, improve soil fertility and control the growth of weeds. It is an important cover crop for plantation crops, especially rubber and oil palm, where it is often grown in a mixture with centro (Centrosema pubescens Benth.) and tropical kudzu (Pueraria phaseoloides (Roxb.) Benth.). In Africa this mixture has been tested in young forest plantations, where it reduced the cost of weeding. Calopo is also used as a green manure for soil improvement. It is grown as a forage, used especially during the latter part of the dry season.

Properties

Although calopo is a widely used green manure crop, little is known about its chemical composition. A chemical analysis of stems and leaves of plants grown in pots in Malaysia indicated per 100 g dry matter: N 3.8 g, P 0.24 g, K 2.0 g, Ca 1.0 g, and Mg 0.25 g. Nitrogen percentages of 2.6-3.8% have been recorded, but lower values should be anticipated in older, stemmy material. Calopo forage is not very palatable to cattle because taste and smell limit the intake, but animals are forced to eat it during the dry season when little green fodder is available. Its low palatibility, which is usually ascribed to the abundance of hairs on the stems and leaves, contributes to its persistence in mixed swards. The weight of 1000 seeds is 13-15 g.

Description

• A vigorous, creeping, twining or trailing herb, up to several m long, forming a tangled mass of foliage 30-50 cm deep, with densely pilose stems with long spreading ferruginous hairs.
• Leaves trifoliolate, petiole up to 16 cm long, pilose; leaflets elliptical, ovate or rhomboid-ovate, (1.5-)4-10(-15) cm × (1-)2-5(-9) cm, the laterals oblique, adpressed pilose or pubescent on both surfaces.
• Inflorescence a slender raceme, up to 20 cm long, peduncle 0-17 cm long, ferruginous pilose.
• Flowers in fascicles of 2-6, blue or purple; calyx campanulate, unequally 5-lobed; corolla with emarginate standard, about 1 cm long.
• Pod linear-oblongoid, 2-4 cm × 3.5-5 mm, straight or curved, softly pilose with coarse reddish-brown hairs, impressed between the seeds, 3-8 seeded.
• Seed compressed squarish, 2-3 mm long, yellowish or reddish-brown.

Growth and development

Calopo grows rapidly and is able to cover the soil in 3-6 months after sowing and even sooner on newly cleared, fertile land. It forms a dense entangled sward in 4-5 months after sowing, but the plants are short-lived and may only persist for 1-2 years. When grown as a cover crop in plantation crops in a mixture with tropical kudzu and centro, calopo is the first to become established but also the first to be shaded out. Long-term persistence is through recruitment of new plants from seedlings. The root system is dense and rather shallow, its deepest roots reaching a depth of about 50 cm. Flowering in calopo is initiated by short days. It is self-pollinated and seeds freely.

Other botanical information

Although widely grown for decades, no improved cultivars of calopo are known to exist. The name "Tortilla" is used to indicate seed of calopo sometimes harvested from naturalized stands in the Adelaide River area of the Northern Territory (Australia). It was at one time thought to have been a long-term locally adapted ecotype, but it is now believed to have come to the area as a contaminant in tropical kudzu seed from Queensland which had been sown in the late 1960s at the Tortilla Flats Research Farm. "Tortilla" is likely to be similar to Queensland commercial material, which is rarely harvested and has never been assigned a cultivar name.

Ecology

Calopo is grown from sea level to 2000 m altitude, but is best adapted to altitudes 300-1500 m. It is well suited to the hot humid tropics with an annual rainfall exceeding 1250 mm but not tolerant of frost. It is moderately drought-tolerant but may die out if the dry season is prolonged. Vigorous growth occurs on soils of all textures, even those with a low pH(H₂O) range of 4.5-5. Its self-seeding nature and twining growth habit make calopo well adapted to a range of ecological conditions. When grown for forage it can be used in a mixture of species, provided it does not become too dominant.

Calopo is poorly adapted to shade, showing a marked decline in top growth, root growth and nodulation with decreasing light intensities. This may be attributed to the "non-plasticity" of leaves under shade as compared with other, shade-tolerant plants such as Calopogonium caeruleum (Benth.) Sauv., Centrosema pubescens and Desmodium heterocarpon (L.) DC. ssp. heterocarpon var. ovalifolium (Wallich ex Prain) Rugayah. Under low light intensities (< 20%) calopo leaves are reduced in size by 70% compared with leaves in full sunlight. In contrast, centro and C. caeruleum leaves are reduced by only 10-25%, while leaves of Desmodium heterocarpon ssp. heterocarpon var. ovalifolium are 20% larger under such a low light intensity.

Propagation and planting

Calopo is usually propagated by seed, sown at 1-3 kg/ha. Seed is normally drilled in rows when sown into new plantations or broadcast in stands to be used for forage production. After seed is broadcast, the seed-bed may be rolled to improve establishment. Newly harvested seed usually has more than 75% hard seed. Mechanical scarification, soaking in concentrated sulphuric acid for 30 minutes, or soaking in hot water (75 °C) for 3 minutes is recommended to enhance germination. Although calopo stems root at the nodes when in contact with moist soil the establishment of stem cuttings inserted directly into soil is generally poor. Use of pre and post-emergence herbicides or hand weeding promotes the establishment of calopo. As calopo nodulates promiscuously with native rhizobia, seeds are usually not inoculated. If inoculum is applied, then cowpea strains such as the Australian CB 756 are used. When planted as a cover crop in plantations it is usually sown in a mixture with other legumes such as Calopogonium caeruleum, Centrosema pubescens and Pueraria phaseoloides with 1-3 kg/ha of calopo in a total mixture of 10-15 kg/ha of legume seed. When sown for forage production, calopo has been successfully used in mixtures with stoloniferous grasses, such as molasses grass (Melinis minutiflora Beauv.) and Rhodes grass (Chloris gayana Kunth), and with tussock grasses such as setaria (Setaria sphacelata (Schumacher) Stapf & Hubbard ex M.B. Moss). Good results have been obtained from oversowing it into existing stands of pangola grass (Digitaria eriantha Steud.) which have been harrowed.

Husbandry

Calopo grows vigorously, shedding a large amount of leaf litter onto the soil which smothers most weeds. Fertilizing acidic soils with ground dolomite and Mo increases yields. Application of P usually increases leaf size. The effect of calopo and associated legumes in improving soil fertility may last for 14-16 years. In an experiment in Malang, Indonesia, a green manure crop of calopo grown for 3 months contained about 65 kg/ha nitrogen in its leaves, shoots and roots. It was followed by a maize crop, which yielded 2.4 t/ha of grain, while a second maize crop following a well-fertilized maize crop had a grain yield of 1.4 t/ha. However, maize following Mucuna pruriens (L.) DC. cv. group Utilis or Crotalaria juncea L. gave significantly higher yields.

If calopo is grazed it is advisable to use rotational grazing with rest periods of 8-12 weeks if calopo growth is erect rather than prostrate. Regular slashing is needed when calopo is planted as cover crop in young oil palm and rubber plantations, to prevent the cover from overgrowing the trees.

Diseases and pests

Calopo is susceptible to viruses in Costa Rica, Guatemala and Panama. Beetles and leaf-eating caterpillars have been observed on calopo in Malaysia, but they have not been a serious problem.

Harvesting

Whether grazed or cut and fed, calopo is often refused by cattle although they eat it less reluctantly during the dry season. It is usually cut by hand and is seldom conserved as hay or silage.

Yield

When pods are mature, peak dry matter yields of up to 14 t/ha can be obtained in a single cut. Lower yields of 4-6 t/ha per year are obtained when calopo is cut every 9-12 weeks. Seed yields of 200-300 kg/ha have been recorded.

Genetic resources

Collections of calopo are held at the Centro Internacional de Agricultura Tropical (CIAT, Colombia) and the Australian Tropical Forage Genetic Resource Centre (ATFGRC, Australia).

Breeding

There are no known breeding programmes on calopo.

Prospects

Being one of the components of a widely adopted mixture of cover crops, calopo is likely to remain important in plantation agriculture. Its value as a green manure crop in intercopping systems and in rotations with annual crops still needs confirmation. Low palatability may explain why interest in calopo as a forage plant has faded during the last decade. However, this low palatability and resulting persistence may open up opportunities for incorporating calopo into forage systems as a way of improving soil fertility and the growth rate and quality of pastures.

Literature

• Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London, United Kingdom. pp. 328-329.
• Bunting, B. & Milsum, J.N., 1928. Cover crops and green manures. The Malayan Agricultural Journal 16: 256-280.
• Duke, J.A., 1981. Handbook of legumes of world economic importance. Plenum Press, New York, United States. pp. 37-39.
• Hairiah, K. & van Noordwijk, M., 1989. Root distribution of leguminous cover crops in the humid tropics and effects on a subsequent maize crop. In: van der Heide, J. (Editor): Nutrient management for food crop production in tropical farming systems. Institute for Soil Fertility (IB) Haren & Universitas Brawijaya, Malang, Indonesia. pp. 157-169.
• Humphreys, L.R., 1980. A guide to better pastures for the tropics and sub-tropics. 4th ed. Wright, Stephenson & Co., Silverwater, Australia. p. 52.
• McWeeney, C.S. & Wesley-Smith, R.N., 1986. Factors limiting the intake by sheep of tropical legume Calopogonium mucunoides. Australian Journal of Experimental Agriculture 26: 259-264.
• Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. 2nd Edition. FAO Plant Production and Protection Series No 2. Food and Agriculture Organization of the United Nations, Rome, Italy. pp. 224-228.
• Wong, C.C., 1990. Mineral composition and nutritive value of tropical forage legumes as affected by shade. MARDI Research Journal 18: 135-143.
• Yates Seeds, 1987. Better pastures for the tropics. 2nd ed. Yates Seeds, Toowoomba, Australia. pp. 40-41.
• Yost, R. & Evans, D., 1986. Green manure and legume covers in the tropics. Research Series 055. College of Tropical Agriculture and Human Resources, University of Hawaii, Honolulu, United States. p. 14.

Authors

Chen Chin Peng & A. Aminah