Stylosanthes humilis H.B.K.

Leguminosae

Synonyms

S. sundaica Taub.; Astyposanthes humilis H.B.K.

Townsville stylo, Townsville lucerne (Australia); Magsaysay lucerne (Philippines); wild lucerne, alfalfa selvagem, alfalfa de Townsville (Brazil).

A self-regenerating, self-fertile summer annual or short-lived perennial legume with trifoliate leaves and branched stems, ascending or prostrate; can reach a height of up to 0.7 m. Leaflets lanceolate, narrow and pointed. Fruit, a biarticulate pod terminated by a persistent style that gives a beaked appearance. Each loment contains one seed. Six or more pods are produced in each seed head. Under heavy grazing or when plant stems rest on moist soil, adventitious roots are formed on the stems several inches away from the taproot.

Native to north-east Brazil, Venezuela, the drier Caribbean littoral, Costa Rica and the Chitre region of Panama. It is now widespread in the tropics.

Occurs from sea level (510 m at Rodd's Bay, Queensland) to up to 1 500 m in Burma (Snook, personal communication).

In Queensland, it requires more than 550 mm. Davies (1966) suggests a range of 635 to 1 778 mm. Late maturing types can grow from 550 to 1 020 mm. Snook (personal communication) found that it did well in Burma under an annual rainfall of 2 500 mm. Winter rain is detrimental to its performance as it tends to cause secondary fungal infection on over-wintering standing hay. Fisher (1970) found it relatively insensitive to within-season droughts.

Prefers sands and sandy loams, but will grow on heavier types such as the rice lands in Burma (Snook, personal communication), where rainfall is 2 500 mm, falling during seven months, and on heavy rice soils on the Adelaide River, Northern Territory (Northern Territory, 1961). It prefers the soil to be slightly acid. It will nodulate at pH 4.5, or pH 4.0 if the calcium supply is adequate. It has fair tolerance of salinity.

Does not need inoculation, as it nodulates freely with native rhizobia of the cowpea type in the soil. If it is desired to inoculate the seed, the current Australian inoculant recommended is CB756.

Excellent; cattle and other grazing animals quickly spread the seed and it will gradually cover the ground. This factor enables seed to be planted in strips to economize on labour and seed (Graham, 1963b).

Competing tall plants must be removed by heavy grazing, burning or discing. A well-prepared seed bed gives quicker and better establishment but is more costly. Cultivation of strips in natural pasture for seeding is cheaper, and aerial seeding into natural pasture is quite effective but gives slower establishment. Norman (1961) found ploughing to 15 cm, then discing level and broadcasting the seed to be the most effective at Katherine, Northern Territory. For aerial sowing into natural pasture, burning or heavy stocking of the natural grassland immediately before the rains is all the land preparation required. Establishment in contour strips by ground cultivation and seeding about one-quarter of the area is another common practice which succeeds best if the timber has been previously ringbarked.

Townsville stylo is either drilled into a well-prepared or roughly prepared seed bed (Strachan, Lambert and Finlay, 1967) or broadcast from ground machines or from the air. Establishment in cultivated strips has been described and illustrated. With aerial seeding, it is best to divide the ground area into blocks by cutting boundaries with a bulldozer and have flag men to guide the aeroplane. Sowing height is 120 m and the seed used either hulled or dehooked for freer flowing. Seed gives three times the establishment that is obtained from pods. Land should be burnt or stocked heavily before seeding and stocked heavily after seeding to reduce competition from tall grasses. Stocker and Sturtz (1966) found that burning the native Sorghum intrans pasture in the middle of the wet season, during the period of reliable rainfall, and aerial seeding S. humilis at the rate of 2.3 kg./ha pods with 250 kg./ha superphosphate gave good establishment on lateritic red earths in the Northern Territory. For good establishment, the soil should be moist after seeding for two to four days (Sillar, 1969); Norman (1961) suggests that moisture content in the top 15 cm of soil should be above wilting point for five to six days.
Oversowing into natural pastures is also successfully accomplished. Establishment is slower and it may take up to three years to cover the ground adequately, but it is very convenient. Miller (1967) states that a period of four consecutive wet days with at least 25 mm of rain in the first day and 75 mm over the whole period would be favourable for establishment­such conditions occurred 15 times in nine years at Katherine, Northern Territory.

396 000 to 484 000. Percentage of hard seed ,17 to 99 percent at harvest. Hard-seededness of 74 to 99 percent in July had declined steadily to 31 to 49 percent by November (Cameron, 1965, 1967). About 10 percent germination a year is satisfactory in the field. Graham (1963b) recorded germination of fresh seed as 2 to 35 percent.

To improve handling: seed is preferably dehulled or at least debeaked or dehooked so that it will flow more freely through seeding machinery. The hooked pods can be diluted with sand for sowing. To break dormancy: treatment is not usual, as hard seed is an advantage under the irregular climatic conditions in which it is normally sown. Scarification by light abrading in a hammer-mill improves germination. Pelleting is not usual. If the seed is to be pelleted, use rock phosphate as a base. Harty (1967) found that superphosphate at the rate of 308 kg./ha inhibited germination of abraded seed, and so a neutral fertilizer or pelleting should be used with heavy superphosphate dressings. Insect and disease treatment is not usual.

Townsville stylo is one of the most efficient of the tropical legumes in extracting its calcium and phosphorus requirements from the soil. It will grow in soil with as little as 3 to 10 ppm available phosphorus, and so will establish in most soils without P, although it performs better with additional P. It is also tolerant of high manganese and aluminium. It is usual to apply 130 kg./ha molybdenized superphosphate at establishment and about 65 kg./ha straight superphosphate annually thereafter.

• Calcium: 

Townsville stylo gives 64 percent of its maximum yield in the absence of calcium (Andrew and Robins, 1969). The calcium uptake is 1.8 to 2.5 percent of the dry matter (Andrew and Hegarty, 1969). Shaw, Gates and Wilson (1966), analysing the response by applying superphosphate, concluded that the calcium of superphosphate had little effect. However, the calcium concentration of S. humilis is the highest of all the tropical legumes analysed by Andrew and Robins (1969), being 67.5 percent of the total calcium compared with the lowest, 48.4 percent, for Desmodium intortum.

• Nitrogen: 

Kretschmer (1968) found that as little as 27.5 kg./ha N applied after each clipping of a pangola grass/S. humilis pasture eliminated S. humilis after three clippings. Andrew and Robins (1969) found the N content of S. humilis low at 3.28 percent compared with Desmodium intortum; the highest, at 4.23 percent. In association with Rhodes grass, Vallis et al. (1967) found that, with added N, Rhodes grass took up 20 times as much N in the first nine weeks and eight times as much as the S. humilis between nine and 13 weeks. At five weeks, they estimated that 47 percent of the N of the legume growing with the grass had come from the soil. At nine weeks, the cumulative uptake of N by the legume was only 6 percent and at 13 weeks only 3 percent of its total N yield.

• Phosphorus: 

The critical percentage of phosphorus in the plant tops was determined in the field by Jones (1968) as 0.16 to 0.17 percent and the latter figure was confirmed by Andrew and Robins (1969). The plant produced its maximum yield when 500 kg./ha superphosphate were added to the soil. The ability of S. humilis to absorb greater quantities of phosphorus from a soil with low available P has been shown by Andrew (1966), who also found that the uptake of P by excised roots of S. humilis from dilute solutions per unit time was greater than that of Macroptilium lathyroides, Desmodium uncinatum and Medicago sativa. Shaw, Gates and Wilson (1966) showed a fivefold increase in yield from the application of PK and Mo. Phosphorus in the presence of Mo also increased N content. In the field, the yield of dry matter was increased by a factor of 2.4 by superphosphate in the presence of Mo, and the yield of nitrogen grew by a factor of 3.3. They found that the P in superphosphate increased dry matter and that S increased the N content. Heavy dressings of P in the absence of S led to a leaf tip necrosis. Heavy dressings of P also reduced the K content below the critical level and increased the Na and Mg levels. They concluded that S. humilis had a high degree of efficiency in profiting from limited reserves of an essential element by substitution of another. Jones (1968) found that for dry-matter production from a solodic soil in north Queensland, an initial dressing of 370 kg./ha superphosphate gave higher dry-matter yields over three years than yearly dressings of 133 kg./ ha, but annual dressings gave high N and P levels. Norman (1959) increased nodulation by 293 percent with a dressing of 370 kg./ha superphosphate over the nil treatment. Fisher (1970) achieved maximum yields at 625 kg./ha superphosphate but 90 percent of the maximum was obtained with 375 kg./ha and 75 percent with 250 kg./ha.
Although adequate dressings of phosphorus are required to give maximum production of Townsville stylo, too much phosphorus will encourage the legume to such an extent that it will eliminate the associated grass and expose the area to a shortage of dry matter (Woods and Dance, 1970). Fertilizer application should be adjusted to keep about 50 percent legume and 50 percent grass. At sowing, 250 kg./ha superphosphate and 62 kg./ha yearly thereafter gave 90 percent of what was considered to be the maximum yield at Katherine, Northern Territory (Norman, 1965b).

• Potash: 

The critical percentage of potassium in the plant tops was determined by Andrew and Robins (1969) as 0.60; and S. humilis gave 47 percent of its maximum yield at low levels of potassium. Gates, Wilson and Shaw (1966) quoted K percentages of 0.35 to 0.55 percent in the tops of plants showing potash deficiency symptoms. Andrew and Pieters (1970a) showed a normal plant to have 1.22 g of K per 100 g of dry matter and a deficient one to have 0.30 g K/100 g dry matter. In plant analyses under differing degrees of K fertilization, S. humilis was found to have low concentrations of K (11 percent compared with D. intortum, which was the highest of eight tropical legumes, with 29.1 percent) . It had high concentrations of Ca, Mg and Na and low concentrations of N and P.
Deficiency symptoms for potash are first evident on the leaves of the middle portions of the plant. They commence as a series of rust-coloured spots of pinhead size, irregular in shape, largely interveinal, but in some cases also on the veins, spread at random over the leaflets. They may or may not be associated with chlorotic leaflet tips, which may be preceded by a bronze coloration on the upper leaf surface. With increasing severity, some of the larger of the rust-coloured areas become necrotic and are discernible on both surfaces of the leaflet. This condition intensifies and is followed by severe leaflet tip and marginal chlorosis, culminating in severe necrosis of the affected areas. The necrosis encroaches toward the base of each leaflet, and in some cases ends up as fully necrotic leaves; each leaflet curls inward to give a ball effect. On complete necrosis and death, the leaflets and petioles absciss although sometimes the petioles remain green in colour and intact. Axillary growth is similarly affected. In very severe forms, the unfolding leaflets at-the growing tip become slightly chlorotic and are puckered and pinched at their tips (Andrew and Pieters, 1970a).