Purple pigeon grass

Introduction

Purple pigeon grass (Setaria incrassata) is a perennial spring-growing and summer-growing grass. It is useful for sowing on heavier and medium textured soils in the north-west of the state as a medium to long term productive pasture.

The grass was introduced from Zimbabwe. The variety Inverell was selected by the New South Wales Soil Conservation Service and released in 1981.

Purple pigeon grass is much easier to establish than other introduced summer-growing grasses, particularly under the marginal moisture conditions frequent in the north-western slopes and plains districts.

Pastures based on this grass have potential for high productivity between cropping phases on heavier soils in the north-west of the state.

Long-term persistence of the grass under New South Wales conditions is less than for Bambatsi panic, an alternative grass for heavier soils in the area. Management is a key to enhancing persistence, particularly in relation to nitrogen, which includes maintenance of a legume.

Purple pigeon grass has not been sown sufficiently for an assessment to be made of its potential carrying capacity in the north-west. Feed analysis indicates that the quality of feed produced is comparable to other introduced summer-growing species such as panics and rhodes grass, and superior to many native pastures.

Adaptation

Being a summer-growing grass, purple pigeon grass is best suited to the north-west and, to a lesser extent, northern sections of the Central West Plains and parts of the state that have summer-dominant rainfall.

  • In the west, a minimum average annual rainfall of 450 mm is required.
  • In the east, its potential is reduced at higher altitudes by cool temperatures and a shorter season — temperate winter-growing grasses such as phalaris are often superior at higher altitudes.

Purple pigeon grass will grow on many soil types but will give best results on heavier clay soils. Persistence is inferior on lower-fertility, lighter textured soils, but it responds well to fertiliser applications. It has some tolerance to waterlogging, but is vastly inferior to Bambatsi panic in this respect.

Seed

Seed size is medium, with 560 000 seeds/kg. Seed cost varies with supply and can be expensive from time to time.

Do not sow freshly harvested seed. Store it for at least one season before sowing. The germination percentage at 1 year old may be as low as 15%, but 2-year-old seed is better and can have a germination percentage of around 70%.

Seed dormancy assists the survival of purple pigeon grass by enabling seed to survive for extended periods in the soil. Pastures will thicken up slowly from seed as well as spreading from short rhizomes.

Buy certified seed where possible. When purchasing seed, be particularly careful to obtain information on germination and any weed seed present, particularly Parthenium weed.

Sowing

Purple pigeon grass has the advantage over many summer grasses of being easier to establish. Attention to seedbed preparation, sowing time, sowing depth and weed control will assist establishment.

Depth of sowing

Sow at a rate of 2–3 kg/ha into a well-prepared seedbed, to a depth of 1–2 cm. Sowing seed slightly deeper (3–4 cm) can be successful in self-mulching soils. Rolling following sowing can assist. Do not roll crusting soils or if increased erosion risk is evident.

Time of sowing

  • Sow in mid-spring in the east of the plains and on the slopes, but if sowing at this time, ensure that summer weeds will not pose a threat to establishment of purple pigeon grass. If they do, delay sowing to allow for weed control and sow in late summer.
  • Avoid sowing in mid-summer unless good moisture is assured.
  • In areas not subject to severe frosting, late-summer to very early autumn sowings have been successful when moisture is good.

Sowing with other grasses

Other grasses often sown with purple pigeon grass are Bambatsi panic and rhodes grass (e.g. Katambora):

  • Bambatsi panic has the advantages of superior persistence and better tolerance to waterlogging but it has poorer seedling vigour and can cause photosensitisation in livestock.
  • Rhodes grass is useful as it establishes relatively easily, and, because it spreads by runners, it has the ability to cover bare patches in the pasture. It is, however, less tolerant of hard grazing.

When including other grasses, the sowing rate of the pigeon grass can be reduced slightly.

Sowing with a legume

A legume well adapted to the area should be grown with the grass, unless naturalised medics are present or expected to regenerate.

  • On the plains to the east, a mid to long season aphid-resistant barrel medic (e.g. Sephi) is suitable.
  • To the west, an early-maturing aphid-resistant variety (e.g. Caliph) is suitable.

These types have less spiny pods than the naturalised medics, and better aphid resistance. On the slopes, sub. clover may be better suited, with varieties selected on maturity.

If you are sowing in the early autumn on good moisture, barrel medic or sub. clover at 3–4 kg/ha will form a good mixture. Do not sow annual legumes in spring, as they will fail to set seed, or in late summer, as they are unlikely to survive.

On neutral to alkaline soils, adding snail medic (e.g. Sava) to the mixture at 2 kg/ha has been found useful because of its superior seedling vigour, although snail medic is less attractive to livestock.

If sowing medics or sub. clover in the early autumn, there is a risk of plants being lost if hot dry conditions set in.

If adding a legume after purple pigeon grass is established, use annual legumes that are well adapted to the area. Oversow into good moisture during May using a machine that will cause minimum disturbance. Sowing on the surface without covering the seed requires good follow-up rain and lack of competition to succeed.

Lucerne can also be sown during autumn at 0.5–0.75 kg/ha on well-drained soils. If sowing in spring, sow early on excellent moisture. Lucerne is not as persistent as barrel medic, but, given the selection of a suitable variety and reasonable grazing management, it should last for 3 years in most situations.

Sowing with a cereal

Sowing seed with a cereal as a cover crop has had some success in southern Queensland, the purple pigeon grass not establishing until spring. This method is experimental, but is worth trying on small areas.

Fertiliser

Unless the soil is very high in phosphorus, sow with 125 kg/ha of superphosphate or equivalent (in terms of phosphorus and sulfur content).

Nitrogenous fertiliser can be used to advantage, particularly on soils low in nitrogen. Do not exceed 20 kg N/ha in contact with seed.

Management

  • Purple pigeon grass will establish quickly and grazing is often possible in the first season. Only graze plants that are well anchored by a strong root system.
  • As with most tropical grasses, the quality of feed drops rapidly if plants are allowed to grow rank. Try to keep plants grazed below 0.4 m high.
  • Abundant grass growth in autumn will reduce the quantity of medic that establishes, so graze heavily in late summer to reduce the cover and open up the sward.
  • Where the density of the pasture is poor, allowing the grasses to seed will greatly enhance the chances of the pasture thickening up. Seed drops readily at maturity so there is no need to allow the grass to stand for long periods without grazing.
  • Where lucerne is used in a mixture it is generally impractical to manage the paddock for optimum lucerne productivity by rotational grazing.
  • The persistence of lucerne is favoured by allowing plants to flower regularly. Opportunities may occur where this is possible without jeopardising the overall productivity of the purple pigeon grass or annual medics.

Livestock health

Avoid grazing horses on pastures dominated by purple pigeon grass. Records indicate that hyperparathyroidism (‘big head’) in horses has occurred frequently. Nephrosis or hypocalcaemia has occurred occasionally in ruminants due to the oxalate content of the grass. (See Important notes.)

Insects and diseases

No problems have been encountered so far with insect pests or diseases in New South Wales.

Seed production

Purple pigeon grass is harvested with a conventional header. Where summer rainfall is good, yields in the order of 200 kg/ha/year can be expected from two harvests in a season. Yields as high as 390 kg/ha have been obtained by specialist seed growers in Queensland.

A certification scheme exists in New South Wales for purple pigeon grass. For further information on seed production, contact your nearest district agronomist.

Important notes

Livestock health disorders

Pasture improvement may be associated with an increase in the incidence of certain livestock health disorders. Livestock and production losses from some disorders are possible. Management may need to be modified to minimise risk. Consult your veterinarian or adviser when planning pasture improvement.

Native vegetation

The Native Vegetation Conservation Act 1997 (www.austlii.edu.au) may regulate some pasture improvement practices where existing pasture contains native species.

Further information

Agnote DPI-292 Purple pigeon grass

Agfact P2.2.25 Lucerne for pasture and fodder