Stylosanthes capitata (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Stylosanthes capitata Vogel

Protologue: Linnaea 12: 70 (1838).

Family: Leguminosae

Chromosome number: 2n= 40

Origin and geographic distribution

S. capitata originates in South America where it occurs naturally in sub-humid and dryland areas in north-eastern Venezuela and, mainly, in central-west, south-east and north-eastern Brazil. One cultivar and several experimental lines have spread to other tropical regions for testing, including South-East Asia.

Uses

The main use of S. capitata is as forage in permanent pastures grazed by ruminants.

Properties

S. capitata provides a palatable forage of moderate to high quality, with N concentrations ranging from 2-3.0%, and DM digestibility 55-60%. Phosphorus concentrations in the herbage are moderate to low (0.09-0.18%). There are 400-450 seeds/g.

Description

A perennial herb or sub-shrub, semi-erect to erect, with a strong taproot. Stems many-branched, lignified at the base; under competition ascending up to 1 m; indumentum varying from glabrous to densely pilose, or with scattered bristles. Leaves 3-foliolate; stipules oblong, 16-20 mm long (including teeth) and 6-8 mm wide, with 2-3 pairs of veins; petiole 2-6 mm long, densely villous; rachis up to 3.5 mm long; leaflets broad-elliptical, oblong or sometimes obovate, 15-40 mm × 5-15 mm, apically acute, mostly densely villous on both surfaces, with 8-12 pairs of conspicuous veins. Inflorescence a capitate spike, terminal or axillary, cylindrical-ovoid, up to 7 cm × 15-20 mm, many-flowered; often several inflorescences in dense clusters; bracts 1-foliate, oblong, 9-13 mm long, with 3-5 pairs of veins, and variable pilosity; flowers papilionaceous, small, with obovoid standard 4-6 mm long, sulphur-yellow; axis rudiment and 2 inner bracteoles present. Pod 2-articulated, 5-7 mm × 2-2.5 mm, reticulately nerved; both articles usually fertile, the upper one glabrous and with a straight to uncinate beak about 1 mm long. Seed colour varying from yellow, sometimes slightly mottled, to almost black.

Growth and development

Initial growth of S. capitata is slow. Flowering and seed setting occur mainly during the end of the rainy season and extend into the dry. Being a very prolific seeder, S. capitata regenerates through seedling recruitment. If plants are allowed to set seed in the year of establishment, more than 1 t of seeds in pods per ha can be produced. The species tends to behave like an annual and plants seldom live longer than 2-3 years.

Other botanical information

To date, S. capitata has become a commercial pasture legume only in Colombia, South America, where a blend of five similar ecotypes was released as "Capica". The objective of blending was to broaden the genetic base of the cultivar and to decrease the risk of anthracnose susceptibility.

Ecology

S. capitata is best adapted to tropical savanna ecosystems with a sub-humid to humid climate characterized by relatively high rainfall (1000-2500 mm/year) during a growing season of 6-9 months. The species requires light-textured, well-drained, acid soils, and has a good tolerance of toxic levels of soil Al and Mn. It grows well on soils of poor fertility, including low available P. Savanna ecosystems with such soils are common in tropical America; their South-East Asian equivalents would be Imperata cylindrica (L.) Raeuschel grasslands in somewhat drier areas with ultisols as the predominant soil type.

Agronomy

S. capitata is drilled in rows or broadcast, preferably with a grass, at a rate of 2-3 kg/ha. Germination of fresh seed is poor because of a high degree of hard-seededness; this can be overcome by mechanical or acid scarification, or by hot-water treatment. Successful S. capitata associations have been obtained with Andropogon gayanus Kunth (gamba grass), Brachiaria decumbens Stapf (signal grass) and Brachiaria dictyoneura (Fig. & De Not.) Stapf. Although the legume nodulates with native rhizobia, inoculation of seed with a Bradyrhizobium strain of known effectiveness is recommended.

Fertilization with P and K enhances establishment, and despite its low soil-fertility requirements, S. capitata responds to maintenance fertilization with these nutrients. It persists well in association with a strongly competitive grass such as Andropogon gayanus , even under fairly uncontrolled grazing, but the use of intermittent grazing systems is suggested.

S. capitata has proved to be very tolerant of anthracnose ( Colletotrichum gloeosporioides ), the major disease affecting Stylosanthes spp. There are, however, regional differences, depending on anthracnose-strain virulence. A common pest is the pod-borer Stegasta bosqueella ; it can drastically decrease seed yield.

In pure legume stands, DM yields of 1-3 t/ha every 12 weeks are obtained during the rainy season. Dry-season yields can be very low, as plants will eventually shed their leaves completely under severe drought. Nevertheless, year-round animal production can be improved due to the presence of S. capitata in a pasture. For example, in a mixture with A. gayanus , liveweight gains of 150 kg/steer per year have been measured compared with 110 kg/steer per year in A. gayanus alone.

Genetic resources and breeding

The species has been widely collected and there is a large, very variable collection available at CIAT (Colombia). A S. capitata breeding programme, aimed at adapting "Capica" to the higher anthracnose-stress conditions of central Brazil is now being concluded.

Prospects

Because of such characteristics as outstanding adaptation to acid and poor soils, disease resistance, long-term persistence through seedling recruitment as a result of high seed production, and good forage quality, S. capitata is an important pasture legume for low-input production systems on marginal soils in tropical savanna regions. Efforts to improve its dry-season performance seem to be justified.

Literature

• Instituto Colombiano Agropecuario, 1983. Capica (Stylosanthes capitata Vog.). Boletín Técnico No 103. ICA, Bogotá. 12 pp.
• Stace, H.M. & Edye, L.A. (Editors), 1984. The biology and agronomy of Stylosanthes. Academic Press, Sydney. 636 pp.
• Thomas, D. & Grof, B., 1986. Some pasture species for the tropical savannas of South America. I. Species of Stylosanthes. Herbage Abstracts 56: 445-454.

Authors

R. Schultze-Kraft