Desmanthus (Desmanthus virgatus) 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 west as far as Roma and Emerald. It needs an annual rainfall of 550-750 mm.
Desmanthus is a productive, drought-tolerant perennial legume. It is very palatable to livestock, has a high digestibility and protein content, and does not cause bloat. 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 120-230 cm.
When to sow
Desmanthus should be planted in early or mid-summer (October/November or January/February).
A prepared seedbed may range from a roughly disturbed soil after a cultivation to control weeds, to a fully prepared seedbed that has been fallowed for moisture and nitrogen accumulation and for weed control. The chances of establishing a pasture improve if sub-soil moisture is good at sowing. Depending on soil depth, aim for a minimum of 40 cm of wet soil under the seedbed. Sowing into a dry profile is a recipe for establishment failure.
Sow 1-2 kg/ha, as a mixture with summer grass seed.
Freshly harvested seed has a high percentage of hard seed and should be treated prior to sowing. Germination percent of the seed should be 50-70%. Seed purchased from merchants should have been scarified so as to improve germinating ability.
Hard seed can be treated by mechanical scarification, or by immersing seed in boiling water for four seconds, then quickly draining the seed and spread it to cool.
Inoculation has been a problem with desmanthus. Research has now developed a better strain of rhizobium, which will be more effective in Queensland. The specific inoculum is available from seed merchants. Pelleted seed with the correct rhizobium is also available.
Sowing method and sowing depth
Seed may be broadcast onto the dry seedbed surface, or drilled shallow into the seedbed with precision planters fitted with presswheels to consolidate the row. The small seed should not be covered by more than 10 mm of soil.
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 pasture seed is not being buried by more than 10 mm of soil or the seedling may not have the energy to emerge and establish.
Broadcasting seed after soil disturbance by cultivation, a burn or after heavy grazing of grass plants, can be successful if very favourable seasonal conditions. If conditions are hot and dry after sowing then the risk of poor nodulation is high. A lack of nodulation will lead to increased seedling death.
A bandseeder is a tined machine that plants legume seed in narrow furrows and removes grass competition by spraying a band of glyphosate herbicide over the seed rows. Planting should be delayed until good rain has fallen to allow existing grass to regrow (glyphosate being effective only on green leaf), and to provide moisture to germinate the seed and support the legume seedling.
Other methods of pasture disturbance and seed distribution, like with the 'crocodile seeder', have also been successful.
Sowing dry ensures that 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 about 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.
In established stands most broadleaved weeds should be suppressed by a dense vigorous pasture growth. It is impractical to use herbicides for broadleaf weed control although a number 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.
Successful pasture establishment can depend on grazing management adopted in the first year. Do not graze until follow-up rainfall allows seedlings to develop a strong root system. It is important to allow the plants to set some seed in the first year.
Desmanthus has been grown successfully on brigalow clay soils, open downs and alluvial country. The high phosphorus levels of most of these soils will be adequate for good plant and animal growth, but poorer soils could benefit from an application of superphosphate. A sulfur deficiency can be corrected by an application of gypsum, elemental sulfur or 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.
Desmanthus can seed heavily under grazing; this allows the stand to thicken up from new seedlings while providing a good soil seed reserve compensating 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 conditions and where plants have been heavily grazed to small crowns, survival has been good and there has been rapid regrowth from these crowns following summer rain.
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