Stenotaphrum secundatum (PROSEA)
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Introduction |
Stenotaphrum secundatum (Walter) O. Kuntze
- Protologue: Revis. gen. pl. 2: 794 (1891), (" secundum ").
- Family: Gramineae
- Chromosome number: 2n= 18, 27 (triploid), 36 (tetraploid), 54 and 72
Vernacular names
- St. Augustine grass, crab grass, buffalo grass (En). Gros chiendent (Fr)
- Vietnam: co'quai chèo.
Origin and geographic distribution
Although its natural distribution is on the shores of the Atlantic Ocean, St. Augustine grass is now found quite extensively in Australia and the Pacific, too, always in coastal areas. In cultivation it occasionally occurs outside its natural range.
Uses
St. Augustine grass is used for grazing in open areas, but is also showing considerable promise for use under plantation crops. It is also a popular lawn grass and is used for soil conservation.
Properties
The quality of St. Augustine grass declines throughout the growing season, with N concentrations between 2.6% and 2.0%. Digestibilities of crude protein decline from 53% to 31% and DM digestibilities from 60% to 50%. It is palatable when young, but palatability of old material is low.
Botany
A stoloniferous perennial with upright or ascending stems, often much branched, 10-50 cm tall. Leaf-sheath tightly compressed and keeled; ligule a ring of hairs, 0.5 mm high; leaf-blade oblong-linear, 3-15 cm × 4-10 mm, plicate when young, obtuse, glabrous, slightly bluish. Inflorescence terminal or axillary, 5-10 cm × 5-10 mm, composed of 10-20 racemes each 0.5-1 cm long and bearing 1-3 spikelets; main axis thick, corky, flat on one surface, deeply hollowed out on the other, each cavity containing a raceme, borne alternately on either side of a wavy midrib; spikelets sessile, lanceolate, up to 5 mm long; lower glume 1-2 mm long, nerveless; upper glume 4-5 cm long, 5-7-nerved; lower floret neuter, upper floret bisexual. Caryopsis oblongoid to obovoid, about 2 mm long.
A form with abnormally slender inflorescences occurs in South Africa and Brazil (called "Natal-Plata deme" by Sauer); a form with almost strobiloid inflorescences is a sterile triploid and occurs in South Africa, Australia and the Pacific islands (called "Cape deme" by Sauer).
The species only flowers occasionally in the wet tropics, hence seed production is very poor. The most popular cultivar for lawns, "Roselawn", is used in several countries.
Ecology
St. Augustine grass is primarily a coastal pioneer. It occurs at altitudes from sea-level up to 800 m, and could well grow at higher elevations than this as it is one of the more cold- and frost-tolerant tropical and warm temperate grasses. It grows in relatively humid areas, preferring fertile soils, although it is also well-adapted to organic sandy soils in Florida (United States) and to alkaline soils. In Puerto Rico it grows well on soils rich in lime and on sandy soils on sloping hillsides. It responds to fertilization on poorer soils. It tolerates short-term flooding and salt spray, but it does not persist where there is a prolonged dry season and on soils with a shallow water table. St. Augustine grass is shade-loving and produces higher yields under shade intensities of as low as 40% sunlight than in full sunlight. Its productivity is maintained with 40% full sunlight.
Agronomy
St. Augustine grass is propagated by planting sections of rooted stolons, preferably early in the wet season. The sections can be planted about 30 cm apart in rows 60-70 cm apart, or else scattered on the soil surface and disked in. One ha of grass will provide sufficient cuttings to plant 10 ha. The stolons grow quickly, although it may still take 5-6 months to form a complete cover. Sward formation is faster under light to moderate shade than in the open. Once established, the dense swards resist weed invasion. Because of its low growth habit, St. Augustine grass is usually grazed, although it can be cut for hay or silage. It should be closely grazed, and grazing every 12-14 days to a height of 5 cm or less has been suggested. When used as a lawn, it should be regularly and closely mown. In one study, St. Augustine grass yielded 5.5 t/ha of DM per year in full sunlight, as measured over 6 harvests. Corresponding yields under 70%, 50%, 40% and 20% sunlight were 3.5, 4.0, 4.9 and 1.9 t/ha. At 40% light transmission St. Augustine grass can attain its maximum yield and can outyield signal grass ( Brachiaria decumbens Stapf).
Nitrogen-fertilized pastures of St. Augustine grass have produced over 1000 kg/ha of liveweight gain per year in the United States. St. Augustine grass-siratro ( Macroptilium atropurpureum (DC.) Urban) pastures beneath a sparse coconut plantation in Vanuatu gave annual liveweight gains of 275-400 kg/ha. However, only 1-2 head/ha could be sustained during the growing season under a denser stand of coconuts at a 9 m spacing.
Genetic resources and breeding
Evaluation of a range of accessions of St. Augustine grass is being carried out in South-East Asia by ACIAR.
Prospects
With the recent emphasis on development of farm systems involving the integration of livestock and plantations in South-East Asia and elsewhere in the tropics, further research on the shade-tolerant St. Augustine grass is warranted. Improving its productivity and seed production would be priority objectives.
Literature
- Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 284-285.
- Reynolds, S.G., 1988. Pastures and cattle under coconuts. FAO Plant Production and Protection Division Paper 91. FAO, Rome. pp. 71-72.
- Samarakoon, S.P., Shelton, H.M. & Wilson, J.R., 1990. Voluntary feed intake by sheep and digestibility of shaded Stenotaphrum secundatum and Pennisetum clandestinum herbage. The Journal of Agricultural Science, Cambridge 114: 143-150.
- Sauer, J.D., 1972. Revision of Stenotaphrum (Gramineae: Paniceae) with attention to its historical geography. Brittonia 24: 202-222.
- Skerman, P.J. & Riveros, F., 1990. Tropical grasses. FAO, Rome. pp. 711-713.
Authors
C.P. Chen
