Desmodium heterophyllum
(Willd.) DC.

Hedysarum heterophyllum (Willd.).

Desmodium, senivakacegu, wakutu (Fiji), hetero (north Queensland).

Perennial, prostrate creeper; stems are reddish brown, hairy, freely branching and root at the nodes. Leaves are trifoliate, the terminal leaflet slightly larger and on a longer stalk than the two lateral leaflets. Flowers are reddish-pink and small, about 3 mm long, two to four flowers in subterminal racemes. Indented pod contains three to six light-brown speckled, shiny, kidney-shaped seeds, 2 mm long.

A native legume in the tropics of the Eastern Hemisphere. Occurs in Mauritius, Southeast Asia, Malaysia, Indonesia and is adventive to the South Pacific. It is recorded as a component of lowland pastures in Sri Lanka and Fiji and used as a leguminous cover in the pepper gardens of Sarawak.

At least 1 500 mm, and does well at 3 475 mm at Topaz (Kelly, 1964) and at 4 000 mm in Fiji.

It is adapted to a wide range of soils from sands to clays. Its pH tolerance is also wide but it seems to perform best at pH 5.0. It has no tolerance of salinity.

It is extremely specific in its Rhizobium requirement. Norris (personal communication) has prepared strain CB 2085 for use with this legume.

Excellent; has invaded pastures of Brachiaria and pangola grass pastures in north Queensland (Grof, personal communication). The segmented pods break up when mature and scatter the seed.

It prefers a well-prepared seed bed where sown by seed, less preparation for cuttings.

Seed can be sown by drilling or broadcasting and the cuttings (Payne et al., 1955) dibbled or disced in. Oversown into pastures, it invades short grass pastures of Brachiaria and pangola grass. Should be sown no deeper than 0.5 cm, preferably in midsummer.

To break dormancy: fresh seed gave 50 percent germination. Treatment with concentrated sulphuric acid for ten minutes increased germination to 91 percent (Grof, personal communication). Roberts (personal communication) scarified the seed mechanically for pot trials. Inoculation is absolutely necessary.

Little is yet known of its nutrient requirements but it responds to superphosphate where the soil is deficient in phosphorus.

It is particularly successful with Brachiaria decumbens and pangola grass in north Queensland and with pangola grass and Brachiaria humidicola (dictyoneura) in Fiji, where it coexists with Centrosema pubescens, Ischaemum indicum and Dichanthium caricosum.

Grof has recorded 60 kg./ha in north Queensland. The inclusion of D. heterophyllum in a pangola grass sward increased the nitrogen content of the grass from an annual mean of 0.86 percent to 1.12 percent. The nitrogen content of the legume averaged 2.8 percent for the season (Grof, personal communication).

Highly tolerant of defoliation and will stand heavy grazing.

Keep companion grass short for best performance. Response to fire. Will not tolerate fire.

Self-compatible but normally cross-pollinated. Chromosome number 2n = 22.

Dry-matter and nitrogen yields obtained by Grof (personal communication) for grass alone, for grass plus legume and for grass plus legume with added nitrogen at South Johnstone, north Queensland, are given in Table 14.2.

Its slight unpalatability enables it to spread early. It is ultimately heavily grazed.

None observed

The short stoloniferous habit of growth and uneven ripening of the pods make seed harvesting difficult. Material is harvested by forage harvester and seed reclaimed from the dried material (Grof, personal communication). Some form of vacuum pick-up would probably perform well (Roberts, personal communication).

Grof harvested just over 5 kg. of seed from 0.17 hectare at South Johnstone.

Susceptible to legume little-leaf, but this is of little consequence under grazing.

Adaptability to a wide range of soils; compatibility and long-term persistence in closely grazed swards of pangola grass and Brachiaria decumbens; free-seeding habit (it spreads readily even under heavy stocking). It is accepted by the grazing animal.

Difficulty of seed collection; susceptibility to frost.

No grazing trials.

Excellent provided the weeds are low growing.

Roberts (personal communication) states it is quite drought-tolerant in Fiji. It is also tolerant to short-term flooding, and Roberts is interested in it for rice fallows in Fiji.

Perennial summer-growing legume; optimum temperature for growth about 25°C (Grof, personal communication); minimum temperature about 12.5°C. It is easily killed by frost.ð

It occurs from the equator to about 20°S. Recorded from sea level to 200 m, but occurs up to 770 m at Topaz in north Queensland and at 900 m in Fiji (Roberts, personal communication).

It grows vigorously over the summer months. Response to light. Shade-tolerant. Flowers in 150 days at South Johnstone, Queensland.