Desmanthus (Desmanthus sp) is a summer-growing legume adapted to neutral to alkaline, medium and heavy-clay soils in the drier subtropical environment. This drier region extends from the New South Wales border to Collinsville in the north and as far west as Roma and Emerald. Desmanthus needs an annual rainfall of between 400-1000 mm.
Desmanthus is a productive, drought-tolerant perennial legume. It is very palatable to livestock, has a high digestibility and protein content, does not cause bloat and has persisted for more than 20 years when successfully established in grass pastures. It is defoliated by heavy frosts but will regrow from crowns after good rain in early spring. Its main role will be to improve native and sown pasture. While performing well in trials, it has yet to realise its commercial potential.
Marc is an early flowering variety which can grow to a height of 30-60 cm and spread to a diameter of 30-80 cm.
Progardes is a recent release comprising a mix of 5 Desmanthus selections with varying maturities and habits. Selections were made with a focus on persistence, productivity and palatability. It is well suited to heavy textured soils.
When to sow
Desmanthus should be planted early in spring or mid-summer (September or January/February or into March in central Qld).
Dropping legume seed directly into established grass pasture is not recommended as it's a high risk operation with low success rates for establishment.
Planting legume seed directly into grass or into a poorly prepared seedbed such as a roughly disturbed soil through blade ploughing is not recommended. Both of these are higher risk options because the grass competition will not be controlled effectively and there is no stored water in the soil profile. Sowing into a dry profile is a recipe for establishment failure.
A well prepared seedbed could range from sprayed out and fallowed strips through grass, to a fully prepared seedbed that has been fallowed for moisture, nitrogen accumulation and for weed control. Cultivation allows the use of pre-emergent herbicides to control both grass and broadleaf weeds. The chances of establishing a pasture improve if sub-soil moisture is good at sowing. Depending on soil depth, aim for a minimum of 50-60 cm of wet soil under the seedbed.
In new sowings of a grass/legume pastures plant at 1-2 kg/ha, in the mixture (i.e. 1kg of pure live seed). When sowing into prepared strips through existing grass pastures, the rate at which the seed is sown/ha can be reduced calculated on the width of the grass strips.
Freshly harvested seed has a high percentage of hard seed and should be treated prior to sowing. Seed purchased from merchants should have been scarified so as to improve germination.
Hard seed can be treated by mechanical scarification.
Desmanthus seed should be inoculated with the correct strain of bacteria (Leucaena/Desmanthus inoculant) to enable the legume to fix nitrogen from the atmosphere. Sowing the seed just before a rainfall event will enhance the inoculant survival. Pelleted seed that contains the correct rhizobium is also available but should be sown soon after pelleting to improve bacteria survival. A lack of nodulation will lead to reduced plant production.
Sowing method and sowing depth
Treating pasture legume sowings like you would a crop should result in a successful establishment. There is little to show from the many kilograms of seed flown or broadcast into unprepared seedbeds in the past.
Seed may be broadcast or drilled shallow into the seedbed. The small seed should not be covered by more than 10–20 mm of soil.
Sowing the seed on a dry surface with stored moisture in the soil ensures that the pasture seed is in the right position to take advantage of the next rainfall to start germination. The seed must maintain close contact with wet soil for at least three days to establish a seedling. Sub-soil moisture will sustain the seedling until follow-up rainfall occurs.
Pasture seeds in the bottom of shallow tine furrows or small depressions in more roughly prepared seedbeds are more likely to establish seedlings because of accumulated water that keeps the soil wetter for longer after rain.
Seed-to-soil contact may be improved on non-crusting soils by rollers or press wheels that will firm the soil around the seed. Be careful if harrowing after sowing that the small seed is not being buried too deep as the seedling may not have the energy to emerge and establish.
Broadcasting seed soon after spraying or soil disturbance by cultivation can be successful if very favourable seasonal conditions occur. If conditions are hot and dry after sowing then the risk of seedling survival is low.
It is possible to use herbicides for broadleaf weed control and a number of chemicals are registered for this purpose. Care should be taken in their selection to avoid killing useful pasture legumes. For further information on herbicide selection consult your agronomist.
Desmanthus has been grown successfully on Brigalow clay soils, open downs and alluvial country. Desmanthus planted in soils low in phosphorous would benefit from an application of superphosphate. A soil test will determine the need for fertiliser. A sulfur deficiency can be corrected by an application of superphosphate.
Pests and diseases
A native psyllid (small aphid-like insect) can attack desmanthus leaf tips, causing crinkling and yellowing of the leaflets, and even death of plants. It has been prevalent in the coastal areas, late in the growing season.
Successful pasture establishment can depend on grazing management adopted in the first year. Do not graze until seedlings have developed a strong root system. It is also very important to allow the plants to flower and set seed in the first year.
Desmanthus can seed heavily under rotational grazing. This seeding allows the stand to thicken up from new seedlings while providing a good soil seed reserve which compensates for plant death in older stands. However, because the hard seed requires weathering to soften, seedling recruitment may be delayed for up to two years following seed set
Frost, short growing seasons, low rainfall and heavy grazing can limit seed production.
Established plants of desmanthus can survive for a long time (more than four years) in pastures that are grazed throughout the year. Even under drought, survival has been good and there has been rapid regrowth from these crowns following summer rain.