DESMANTHUS: A PROMISING SUMMER PASTURE LEGUME FOR CLAY SOILS
Desmanthus virgatus is a perennial summer growing legume suitable for growing on clay soils in tropical and sub-tropical northern New South Wales and Queensland. It is native to central and southern America where it grows on neutral to alkaline soils in areas of low rainfall. Unlike other tropical legumes currently available to livestock producers for sowing in heavy soils, desmanthus is well suited for use in extensive grazing areas of native and sown grasses.
WHERE WILL IT GROW?
Desmanthus has been grown experimentally from northern NSW in the south to Collinsville/Townsville in the north and west as far as Roma, Emerald and Julie Creek.
(i) Soils Desmanthus is suited to medium and heavy textured clay soils with neutral to alkaline soil pH (Ph > 6.5). It has been grown successfully on brigalow clay soils, open downs and alluvial country. Most of these soils are high in phosphorus and soil P will be adequate for high plant and animal growth, but some soils will have inadequate levels of P and may benefit from adding fertilizer. Also, desmanthus may respond to added sulphur on soils that are known to be deficient.
(ii) Rainfall Desmanthus is adapted to areas with annual rainfall of 550 to 750mm.
(iii) Temperature Desmanthus is a tropical legume but has some frost tolerance. It is defoliated by heavy frosts but regrows from crowns in the spring once there is sufficient soil moisture.
Desmanthus can either be planted into cultivation or by over sowing existing grass pastures, either using the bandseeder or during pasture renovation. When over sowing, establishment will be more successful if competition from the existing native or sown grasses is reduced. For example, if using the bandseeder planting should be delayed until after rainfall. This allows grass to regrow and be killed by spraying and also provides subsoil moisture for seedling growth. Plant in early to mid-summer (October/November to January/February) in mixtures with Desmanthus is relatively small seeded (300,000 – 320,000 seeds/kg) and so depth of sowing and seedbed condition can have a large effect on establishment. Seed should be sown at depths no greater than 10-15 mm and rolling could be a benefit particularly on fluffy seedbeds. Sowing rates should be at least 2 kg/ha.
- Seed treatment Freshly harvested seed has a high percentage of hard seed and seed treatment is necessary to increase the proportion of soft, readily germinable seed. Seed purchased from merchants will have been treated. A level of 50-70% soft seed is best as it allows for good germination on the first rain after sowing – but leaves some seed in reserve in case the first emergence dies due to lack of follow-up rain.
Hard seed can be treated by mechanical scarification (usually done by the seed merchant) or hot water treatment by immersing seed in boiling water for 4 seconds, quickly draining and spreading to cool. Seed should be re-tested for germination after treatment to ensure that there is adequate soft seed.
- Seed inoculation To promote nodulation and nitrogen fixation, a specific inoculum (CB3126), which can be bought from seed merchants, should be used. The inoculum is stuck to the seed with a dilute sticking agent such as Methofas (1%) milk, or a weak sugar solution. While continuously stirring or mixing the seed, apply enough sticker to the seed so that seeds are sticky but not adhering to each other. Then add the required amount of inoculum as described on the inoculum package and mix thoroughly. Dry the inoculated seed in the shade and plant as soon as possible.
Marc – an early flowering cultivar which can grow to a height of 30 to 60 cm and spreads to a diameter of 120 to 230 cm. This cultivar is originally from Argentina.
Marc is protected by Plant Variety Rights and marketed exclusively by Progressive Seeds Pty. Ltd.
PRODUCTION AND PERSISTENCE
Desmanthus is a productive, persistent, drought tolerant legume that is well eaten by livestock.
Marc Desmanthus, can seed heavily under grazing. This means that stands can thicken up through seedling recruitment following good rainfall. It is important to ensure a good seed set in the first and second year after planting – and periodically thereafter – to build up a soil seed reserve. This seed reserve is needed for the seeding recruitment required to compensate for the death of plants in older stands.
Frost, short growing seasons, low rainfall and heavy grazing can limit seed production. Also, seedling recruitment can be delayed until the second year after seed set because the hard seed requires some period of field weathering to soften and germinate.
In combination with perennial grasses, such as buffel, Floren, Strickland, Bambatsi panic, Desmanthus has yielded 1 to 2 tonnes of dry matter per hectare and up to 3 tonnes in pure swards.
It does not cause bloat and digestibility and protein content are high although less than for leucaena. Established plants of desmanthus can survive for a long time (>4years) in pastures that are grazed throughout the year. Even under drought conditions and where plants have been heavily grazed to small crowns, survival has been good and there had been rapid regrowth from the crowns following rain.
PESTS AND DISEASES
A native psyllid (small aphid like insect) can attack desmanthus stands causing some leaf yellowing and even death. It has been more prevalent in the coastal areas and late in the growing season.
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