Latin name: Stylosanthes guianensis (Aubl.) Sw. var. intermedia (Vog.) Hassler.
Synonyms: S. montevidensis Vog. var. intermedia Vog. and others according to 't Mannetje (1977) and (1984), but Williams et al. (1984) regard it as S hippocampoides Moh., and could well be right. Agronomically fine stem stylo is quite a different plant to the var. guianensis stylos.
Common names: Fine stem stylo.
Family: Fabaceae (Leguminoisae)
Stylosanthes guianensis, credit photo from flickriver.com
A semiprostrate perennial with a strong taproot. Differs from common stylo in having a well-developed crown with buds both below and above ground level. It also has finer stems and smaller leaflets. The narrow deep green leaflets are 1.5 to 3.5 cm long, 3 to 5 mm wide and have few hairs It has 4 to 20 small yellow flowers subtended by leaflike bracts in small compact spikes. Flowers are mainly terminal but sometimes occur in the leaf axils. The light brown pods are flattened, single-seeded, 3 mm long and 2 mm wide with a minute coiled beak; conspicuously fine-veined without hairs. Pods fall as they ripen. Seeds are yellowish brown (Davies and Hutton, 1970). Very little root development occurs at the nodes of prostrate stems except under high moisture conditions, and even then rather poorly (Stonard, 1968). It was introduced to Australia by W. Hartley, as CPI 11493, from sandy loam at Asunción, Paraguay.
It is found in Paraguay, Argentina, northern Uruguay and southern Brazil, extending to latitude 33°S.
Season of growth
Comes away earlier in the spring than other legumes grows through the summer with peak growth in November and in the absence of frosts grows into the winter. It is perennial in habit and has a longer growing season that S. humilis.
In Queensland, it is grown at 100 to 130 m, in Paraguay it occurs at about 200 m (Fretes, Samudio and Gay, 1970).
Mediumfrom 625 to 875 mm in Queensland. In Paraguay it occurs in a rainfall zone of 1 300 to 1 500 mm.
Prefers sands and sandy loams, but will establish on basalt loams. Does not establish on heavy self-mulching clays. Has a wider range of adaptability than common and Townsville stylos. It grows best in soils of pH 6.5 to 6.7. Its tolerance of salinity is unrecorded.
Although it may nodulate weakly with some local rhizobia and those of the cowpea type, it requires a specialized Rhizobium for best growth. The current (1970) Australian recommendation is CB1552. The nodules are small and irregular in shape and are found mainly on the taproot seldom on the laterals (Stonard, 1968).
Ability to spread naturally
Quite good in suitable soils. At Brian Pastures, Queensland, it has spread on granitic sands with the aid of grazing by cattle, hares and wallabies (Stonard, 1968).
Land preparation for establishment
Does not need elaborate land preparation; burn the pasture in the spring, then cultivate lightly.
Seed is broadcast after light cultivation. Oversowing into natural pastures is successful; the area should be continuously stocked after seeding to reduce competition from the grass. Do not sow deeper than 1 to 1.5 cm and lightly cover. Sow in midsummer (during the rainy season) at 2 to 5 kg./ ha.
Number of seeds per kg.
770 000 (Davies and Hutton, 1970). There is a high percentage of hard seed in the pod (Stonard, 1968), which is an advantage in perpetuating the sward under unreliable rainfall conditions.
Seed treatment before planting
To break dormancy: (a) scarify mechanically; or (b) immerse in hot water at 80°C and allow to cool for 40 min.; or (c) treat with concentrated sulphuric acid for 10 min., wash and dry. Inoculation is necessary. Pelleting is not needed unless to protect the rhizobia, when rock phosphate should be used (Norris, 1967). If seed-harvesting ants are troublesome, dust with dieldrin, 13.2 cc of dieldrin 15 percent emulsifiable concentrate (or 2.2 g acid equivalent per kg. seed).
Grows well even on soils of low fertility, but responds to phosphorus and molybdenum.
Phosphorus: Fine stem stylo, like S. humilis, is very efficient in extracting phosphorus from the soil and grows quite well on granitic sands at Brian Pastures, Queensland, with an available P content of 35 ppm. It responded to 250 kg. of molybdenized superphosphate per hectare, which increased total native grass/fine stem stylo yield by 23 percent and the protein content of the grass by 0.47 percent, but not that of the legume.
Tolerance to herbicides: Herbicide responses of Stylosanthes spp. reported by Stonard (1968) are given in Table 14.11.
Nitrogen-fixing ability: Evidence of effective nodulation is provided by Stonard (1968): yield from unfertilized native pasture was raised by 17 percent and from similar pasture fertilized with 250 kg./ha molybdenized superphosphate by 23 percent when fine stem stylo was grown with it.
Response to defoliation
Can stand close grazing; a profusion of short leafy shoots develops from the crown, giving the plant a higher leaf to stem ratio. Grazing management. Can be grazed throughout the year. Stock it heavily after burning native pasture and introducing stylo seed, and again in the autumn to control excessive grass growth.
Response to fire
Survives fire much better than common stylo because of its buried crown, and its seed-shattering habit and hard-seededness allow it to regenerate from seed.
Self-fertilized; chromosome number 2n = 20.
Dry-matter and green-matter yields
In unfertilized natural pasture, Stonard (1968) obtained 637 kg./ha of fine stem stylo in a total yield of 1 735 kg. of mixed natural pasture/fine stem stylo pasture, and 950 kg./ha when fertilized with 250 kg./ha molybdenized superphosphate in a total yield of 2 065 kg./ha. The highest dry-matter yield of legume in a grass/legume mixture was 5 044 kg./ha/year over two harvests when fertilized at 23 kg./ha of P; unfertilized legume yielded a maximum of 2 027 kg./ha (Stonard and Bisset, 1970).
Suitability for hay and silage
No records of conservation are documented. The plant is quite prostrate and would be difficult to cut.
Value as a standover or deferred feed
It is valuable in the absence of frosts.
It is well grazed but no data on live-weight gains are available. Chemical analyses and digestibility are not available. It is a little unpalatable when young, but improves as it matures.
Seed harvesting methods
Ripe seed is exserted from the flower head, making harvesting difficult. The whole plant can be harvested with a rotary lawnmower fitted with a grass catcher when 30 percent of the seed is ripe. The material is then dried and threshed (Stonard, 1968). Otherwise, the seed can be allowed to fall and be sucked from the ground with a vacuum harvester (Bisset, 1968). If the crop is grown for seed production, it can be grown in rows, and, at flowering, plastic strips are laid under the plants to catch seed when it falls on ripening. Seed-harvesting ants may take some seed.
Seed yield: The average yields of seed is 300 to 500 kg./ha, but up to 1 000 kg./ ha have been obtained.
The Oxley fine-stem stylo is the only cultivar of Stylosanthes guianensis var. intermedia in Australia, although unselected material is also available. Several more ecotypes are under test but have not been released for commercial planting.
Extreme tolerance to grazing and fire; drought and some frost resistance; efficiency in extracting calcium and phosphorus from the soil; compatibility with grasses. Strong ability to naturalize on suitable country.
Main deficiencies: Difficulty of seed harvest; specificity of Rhizobium; lack of bulk.
Performance: Dry-matter yields have been given. Main reference. Stonard (1968).
Latitudinal limits: It is used in latitudes 24 to 30°S; its performance elsewhere is not known.
Ability to compete with weeds: In its adapted low rainfall environment, it competes successfully with weeds.
Diseases and pests: Only seed-harvesting ants have been recorded.
Temperature for growth: Optimum approximately 27 to 29°C. It withstands temperatures up to 43°C. Although frosts affect tops, crowns of established plants have survived temperatures of -10°C. In the absence of frost it grows through the winter.
Tolerance of drought and flooding: Has excellent drought-resisting qualities (deep taproot, small leaves); it is unable to withstand flooding.
Vigour of seedling, growth and growth rhythm: Seedlings quite vigorous, but light should be available to them for quick establishment. It has a long growing season (September-April in south-eastern Queensland). Its yield over nearly three years is given by Stonard and Bisset (1970) in Figure 79.
Compatibility with grasses: Combines well with Heteropogon contortus and with buffel (Cenchrus ciliaris) and Rhodes (Chloris gayana) grasses.
Response to photoperiod and light: Fine stem stylo flowers over a long period; grows best in pasture mixtures where there is ample light provided by burning or heavy grazing.