Calopogonium caeruleum (PROSEA)
Calopogonium caeruleum (Benth.) Sauv.
- Protologue: Ann. Acad. Habana 5: 337 (1869).
- Family: Leguminosae
- Chromosome number: 2n= unknown
Stenolobium caeruleum Benth. (1837).
- Caeruleum calopo (En)
- Thailand: thua sealulium.
Origin and geographic distribution
Native to Mexico, Central America and the West Indies and eastern tropical South America, C. caeruleum is now widespread throughout the humid tropics. It was introduced to South-East Asia in 1940.
C. caeruleum is a forage of low palatability, but it gives good soil cover, builds up soil fertility as a green manure crop, and can be used to smother weeds such as Imperata cylindrica (L.) Raeuschel.
Mineral concentrations in top growth usually range from 2.1-3.6% N, 0.17-0.29% P, 2.4-2.6% K and 0.91-1.05% Ca. In vitro DM digestibility was not affected by shading. It is much less palatable to animals than C. mucunoides Desv.
A sturdy, somewhat woody, twining, short-lived perennial with pubescent or glabrescent stems up to several m long, rooting at nodes when in contact with moist soil. Leaves trifoliolate, petiole up to 16 cm long; leaflets elliptical, ovate or rhomboid-ovate, (1.5-)6-9(-20) cm × (1-)4-6(-15) cm, the lateral ones oblique, pubescent above, velvety pubescent below. Inflorescences elongated many-flowered racemes, up to 50 cm long; peduncle 1-5(-17) cm long; rachis sulcate, tomentose; calyx campanulate, 5-lobed; corolla blue or violaceous, ca. 1 cm long. Pod linear-oblong, 4-8 cm × 0.8 cm, straight or curved, impressed between the seeds, pubescent. Seeds 4-8 per pod, orbiculate, 4-5 mm across, shiny brown, compressed.
In the literature, the species name is also written " coeruleum ", but Bentham published the name as " caeruleum " (= blue).
Although it grows vigorously once established, growing as high as 1 m in a pure sward, its growth is not compact and it allows free aeration of the soil. When grown as a cover crop it will smother young oil palms and rubber trees unless weeded out from around the base of the trees. It is a poor seeder in the first and second years after establishment.
C. caeruleum is adapted to the humid tropics but it is more drought-tolerant than C. mucunoides and Pueraria phaseoloides (Roxb.) Benth. It grows better in cooler conditions than centro ( Centrosema pubescens Benth.) and in the elevated tropics can grow up to an altitude of about 800 m. It is very tolerant of shading. C. caeruleum is adapted to a wide range of soil textures and soils with a pH(H2O) as low as 4.0. It grows best on well-drained soils.
C. caeruleum is usually established from seed, sowing at the start of the wet season into a seed-bed prepared mechanically or by hand. Fertilizing and weeding aids establishment and development of the sward. However, the use of C. caeruleum seed is restricted by its high cost, which is a reflection of its poor seed production. It can be vegetatively established from stem cuttings, but only about 5% of the cuttings may establish. The best success is obtained from using older stem material, 50 cm or more away from the terminal growing point. Establishment from stem cuttings can be improved by hormone treatments to induce root development. It is slower to establish than tropical kudzu ( Pueraria phaseoloides ) and may take 20 months to establish a complete ground cover. It persists longer under the increasing shade of young oil palm or rubber than most other legumes. In Malaysia it still produced DM 1 t/ha 5 years after planting.
Although C. caeruleum is a productive species, especially under shade, it has very limited value as a forage because of its low palatability. Experience in Malaysia and northern Australia has shown that it can become dominant in grazed pastures because it is virtually ungrazed, whereas the companion species are selectively grazed. It is probably eaten slightly more during the dry season, when there is less opportunity for animals to graze selectively. The herbage can be harvested and then spread onto the soil and ploughed in as a green manure crop, but it is better to leave the sward untouched and to allow leaf fall and decomposition. Leaf fall can be as much as 7 t/ha of DM per year.
No major diseases or pests have been reported on this species in South-East Asia.
It is one of the most productive herbaceous legumes, with DM yields of 10 t/ha in the year of establishment and up to 15 t/ha in following years. Under low light intensities of 6-16% of full sunlight under an oil palm canopy, C. caeruleum outyielded other herbaceous legumes such as Stylosanthes guianensis (Aublet) Swartz, Macroptilium atropurpureum (DC.) Urban, Centrosema pubescens Benth., Desmodium heterocarpon (L.) DC. ssp. ovalifolium (Prain) Ohashi, Desmodium heterophyllum (Willd.) DC. and Calopogonium mucunoides with DM yields of 1-1.5 t/ha. It also had the best survival rate. No information is available on its use as hay or silage, although it is possible that such treatment could increase its palatablity.
Genetic resources and breeding
Limited collections of C. caeruleum are held by CIAT (Colombia) and ATFGRC (CSIRO, Australia). There are no breeding programmes on this species.
The potential of C. caeruleum as a forage is limited unless genotypes of better palatability can be identified. The potential benefits of using this species to improve soil fertility in farm systems involving forage production could be explored further. It is likely to become a standard component of mixed cover crops in plantation crops.
- Allen, O.N. & Allen, E.K., 1981. The Leguminosae: a source book of characteristics, uses and nodulation. Macmillan Publishers Ltd., London, United Kingdom, and The University of Wisconsin Press, Madison, Wisconsin, United States. p. 127.
- Chen, C.P. & Othman, O., 1984. Performance of tropical forages under the closed canopy of oil palm. Legumes II. MARDI Research Bulletin 12: 21-37.
- d'Arcy, W.G., 1980. Calopogonium. In: Dwyer, J.D. et al. (Editors): Flora of Panama. Annals of the Missouri Botanical Garden 67: 557-561.
- Han, K.J. & Chew, P.S., 1981. Growth and nutrient contents of leguminous covers in oil palm plantation in Malaysia. International Conference on the Oil Palm in Agriculture in the Eighties. Organized by the PORIM and the Incorporated Society of Planters held on 17-20 June 1981 at Kuala Lumpur, Malaysia. Article 30. pp. 182-199.
- Pillai, K.R., Thiagarajan, S. & Samuel, C., 1985. Weed control by sheep grazing under plantation tree crop. In: Sivarajasingam, S. et al. (Editors): Proceedings of the 9th Annual Conference of the Malaysian Society of Animal Production, March 11-12, 1985. Serdang, Selangor, Malaysia. pp. 43-52.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. p. 223.
- Wong, C.C., 1990. Mineral composition and nutritive value of tropical forages as affected by shade. MARDI Research Journal 18: 135-143.
C.P. Chen & Y.K. Chee