Annual medics

A pasture plant from the medic species

Annual medics are temperate legumes from the Mediterranean region

Annual medics have become naturalised in the subtropics of Queensland following their accidental and also deliberate introduction over the last century. They occur in large areas of native and sown pasture, and make a valuable contribution to both the grazing and grain-growing industries.

Annual medics are temperate legumes from the Mediterranean region where the climate is wet in winter and dry in summer. They are self-regenerating plants, surviving through their reserves of hard seed which may lie in the soil for many years. Such a characteristic is an excellent defence in the more variable rainfall conditions of the subtropics, providing many germination/establishment opportunities. This attribute is particularly useful in the dryer western areas.

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Role of annual medics

Barrel and snail medics and naturalised burr medics make a valuable contribution to both grazing and farming systems in Queensland. They are both sources of high quality forage and a plant which can increase soil nitrogen levels. Improved soil nitrogen increases grass production and quality.

Annual medics are valuable when used in rotation with crops to restore and maintain soil fertility. While both snail and barrel medics are used in rotation with crops, snail medic is preferred in southern Queensland.

Aphid attack

Blue green and spotted alfalfa (lucerne) aphids, which can kill or seriously reduce the production of many commercial and naturalised medics, appeared in 1977. Aphid-tolerant medics have since been selected or bred, and today there are a number of these cultivars available for commercial use. This has also been an opportunity to seek cultivars better adapted to the subtropical climate of southern inland Queensland.

Two decades after the appearance of aphids some balance has developed between aphids and predators and the impact of this pest seems less severe than it was originally.

Declining fertility

Declining soil fertility under continuous cultivation and grain cropping has boosted the need for and use of annual medics. Their ability to add considerable amounts of nitrogen to the soil makes them valuable as 'ley' pastures to restore fertility in depleted soils. The snail medics are well suited to crop/pasture rotations.

Where will medics grow?

Rainfall

Medics have naturalised in those areas of southern inland Queensland receiving 400-800 mm of annual rainfall and with 30% or more falling in winter.

Medics need good germinating rain in autumn or early winter, while growth is enhanced by the carryover of sub-soil moisture from summer rains or from summer fallow. Medic growth varies greatly between years associated with variable rainfall and competition. North of about latitude 26° S, competition from summer-growing grasses often inhibits medic growth.

Soils

Most medics prefer neutral to alkaline (pH 6.5-8.0) clay and clay-loam soils of moderate to high fertility although some may tolerate moderate acidity.

Species and varieties

Annual medics belong to the genus Medicago but are often incorrectly called clover or trefoil. Medics have yellow flowers, and clovers white or pink flowers, whereas trefoils are species of Lotus which do not occur naturally in this region.

Naturalised medics

Some annual medics were introduced before the turn of the century. They spread naturally through seed pods caught in animal coats, especially in wool. Common naturalised medics are:

  • Medicago polymorpha - burr medic
  • M. minima - woolly burr medic
  • M. laciniata - cutleaf medic
  • M. lupulina - black medic

Sown medics

Medics commonly sown in Queensland are described below. Ongoing breeding and selection periodically develops new varieties, which are promoted as they become available.

Snail medics (Medicago scutellata)

Snail medics have the largest pods and seeds of the commercial medics. They respond to cultivation and thrive where competition from other species is reduced or removed. They can be grown with winter forage crops, where they compete moderately well. For maximum nitrogen contribution however, snail medics are sown, or allowed to regenerate, as a pure sward.

Sava is an early-flowering variety. When sown or germinating early (April), Sava can make good growth before winter although this may lead to reduced spring production. With winter germination it is slow to grow but will produce well in spring.

Silver (early flowering) and Essex (mid-flowering) are new snail medic varieties with similar attributes to Sava and both are well suited to southern Queensland.

Kelson is late-flowering requiring a period of cold before it can flower. Kelson flowers too late to set seed reliably in southern Queensland. It will continue to produce well into spring when moisture is available, and after early-maturing varieties have finished growing. It is more suited to the higher rainfall areas.

With the availability of three flowering types (early, mid-season and late) it is possible to sow mixtures of snail medics which can be responsive to different types of seasons.

Barrel medics (Medicago trunculata)

Barrel medics are better suited for permanent pastures than snail medics. They are adapted to a range of fertile soils.

Caliph is an aphid-tolerant variety bred from Cyprus. It is early flowering and grows well on soils ranging from slightly acid red-brown loams to clay-loams and clays.

Cyprus is an aphid susceptible variety. It is the most widely distributed commercial medic in Queensland, a position that was once held by Jemalong barrel medic.

Jester is an aphid-tolerant variety bred from Jemalong. It is well adapted to the clay soils in the subtropics and can be identified by the conspicuous spot in the middle of the leaf like its parent. Jemalong will be superseded by Jester.

Paraggio is an aphid-tolerant variety. It will grow on a wide range of soils from hard setting loams to cracking clays. It is the barrel medic variety most tolerant of powdery mildew. This disease has been reducing the production potential of medics during the last decade.

Sephi is an aphid-tolerant variety which performs well on clay soils.

Jemalong is susceptible to aphid damage but is well adapted to clay soils in the subtropics. The build-up of aphid predators appears to have reduced the frequency of damage to Jemalong. However, it will still occur when an aphid attack is severe.

Parabinga is an early-flowering barrel medic more suitable for the drier parts of the region, such as the Maranoa. It has very spiny seedpods.

Mogul is used as an aphid-tolerant replacement for Jemalong in southern States but in Queensland it has not performed as well as Sephi.

Other medics

Toreador (Medicago tornata x littoralis hybrid) is an aphid-tolerant early flowering variety that sets large amounts of hard seed. It should persist well in the dryer areas.

Herald (Medicago littoralis) is an aphid-tolerant variety that has not been widely used in southern Queensland. Performs well in southern Australia but has been average in trials in Queensland.

Harbinger AR (Medicago. littoralis) is one of the 'strand' group of medics and is suited to well-drained alkaline sandy soils. It has not performed well in southern Queensland.

Cavalier and Scimitar (Medicago polymorpha) are spineless burr medic varieties that lack aphid tolerance. They have performed quite well in southern Queensland.

Serena, Circle Valley and Santiago (Medicago polymorpha) are spineless burr medic varieties that lack aphid tolerance. They have not persisted well in southern Queensland.

Aphid tolerance

The aphid-tolerant lines commonly used in Queensland are described as

  • R - resistant
  • MR - moderately resistant
  • MS - moderately susceptible
  • S - susceptible
Table 1: Tolerance of aphids

Cultivar

Spotted alfalfa aphid

Blue-green aphid

Snail medic

  

Sava

R

MS

Kelson

R

MS

Essex

R

MS

Silver

R

MS

Barrel medic

  

Caliph

R

R

Cyprus

S

S

Jester

R

R

Paraggio

MR/MS

R

Sephi

R

R

Parabinga

MS

R

Jemalong

S

S

Toreador

MR

R

Herald

R

R

Harbinger AR

MR

MR

M polymorpha

S

S

Hard seed

A large proportion of the seed set by annual medics has an impermeable coat that prevents water entering and the seed germinating. Hardseed levels will progressively reduce in the soil and soften over a 1-5 year period. This is an important characteristic allowing medics to survive through bad seasons and in marginal areas.

When to sow

April, May and June are the preferred months. The risk of establishment failure is higher with later sowing, while sowing during spring and summer is a waste of seed. On the Darling Downs, sowing tropical grasses and annual medics together in February/March is a compromise and may be successful because of the milder late summer temperatures.

Sowing methods

Sowing a sward or sowing with winter cereals: Sowing pasture seed into a prepared seedbed that has been fallowed to build up sub-soil moisture and control weeds is always preferred. However opinions differ as to the best way of introducing the seed.

Ardent supporters of this legume sow medics as a pure sward to achieve a quick build-up in both soil nitrogen and seed reserves in the soil. Growers introducing medics into their system can undersow the last cereal crop with medics before planting a grass pasture.

Sowing with summer grasses: Medics are a good companion for tussocky grasses. However, the right time for sowing a summer grass is too early for the medics; the right time for the medics is too late for the grasses.

A compromise of February/March has been successful in eastern areas. However, the practice of undersowing wheat with medics in the year(s) before introducing the pasture phase is more effective.

Oversowing into grass pasture: An alternative to sowing at the same time as the permanent summer pasture is to surface broadcast the medic seed later. This method can be used in autumn/early winter of any year after the year of grass establishment.

Reducing competition from grasses by grazing heavily in late summer and for a short time after the seed is broadcast to trample the seed into the soil assists establishment.

A disadvantage with the surface broadcasting method is that hot dry weather and exposure to sunlight may kill the Rhizobium bacteria. Poorly nodulated seedlings have a less chance of surviving. New commercial developments that claim to improve the life of the bacteria on the seed under dry conditions may improve the options for sowing pasture legumes under harsh conditions.

Bandseeding and other methods of disturbing established grasses have also been effective in introducing medics.

Sowing rate

High sowing rates improve early production of pure medic pastures. Sowing rate is:

  • 4-6 kg/ha for snail medic sown as a pure sward
  • 2-3 kg/ha for barrel medic in grass-legume pastures
  • 3-4 kg/ha for undersowing with wheat.

Inoculating seed

Legumes such as annual medics gather nitrogen from the atmosphere and leave it in the soil for other plants to use. They do this more effectively if they are associated with the right strain of bacteria. Medic seed should be inoculated with Group AL inoculum obtained from seed merchants. Acid-tolerant inoculum is available for seed that is to be sown on slightly acid soils less than pH 6.5.

Sowing medic mixtures

Seed of the different medic cultivars are normally mixed. For a ley pasture in crop-pasture rotation, the emphasis is on snail medics with only a small amount of barrel medic, with a mixture of the early-, mid-, and late-season flowering cultivars to take advantage of different length of seasons.

For a permanent grass-legume pasture, the emphasis is on barrel medics with only a small amount of snail medic.

The ideal depth for barrel medics is 10-20 mm (no deeper than 20 mm) when sown into a prepared seedbed. As winter cereals are sown deeper than this, seeding attachments are needed to sow the medic seed at a shallower depth. Medic seed can be surface broadcast ahead of the cereal sowing to allow a shallow placement of the seed.

Snail medic can be sown up to 50 cm deep if sown with a winter cereal. This allows the medic and cereal to be sown in the one operation.

Fertiliser

As medics are adapted to fertile soils, fertiliser is seldom applied. However the most important nutrients for medics are phosphorus, sulfur and calcium. Low phosphorus limits growth and protein content, while medics also need an adequate supply of calcium (greater than 6.0 meq/100 g). Most clay and clay-loam soils have adequate supplies of these nutrients, but potential deficiencies in red earths, loams and hard setting duplex soils are best assessed by soil analysis.

Sulfur deficiency causes pale green leaflets. Applying sulfur has improved medic growth in permanent pasture on the eastern Darling Downs. Although sulfur has been spread by aerial application, operators have required a number of growers to place orders to make the exercise economical.

Broadcasting with ground rigs is usually the only method available to individual growers. Rates of 20-60 kg/ha of elemental sulfur can be applied and will last for a number of years. Sulfur supply will normally be adequate with ley pastures as occasional cultivation will release sulfur for plant use.

Management of medics in sown pastures

Annual medics are variable in their production when grown in permanent grass pasture, mostly due to a combination of variable winter rain and competition from summer-growing grasses, although soil seed reserves and grazing pressure effects production.

Good medic years need a good moisture supply from autumn through to spring. Often they occur after a dry summer when the grass has grown poorly or has been heavily grazed and subsequently provide less cover and competition.

Stock management to favour medic production involves heavy grazing of summer-growing pastures during the late summer/autumn period, leading to open pastures and reduced competition. This practice will cause decline in the condition of a permanent pasture, especially with native grasses, and should not be used regularly.

Sheep will graze the pods of commercial medics and can severely reduce seed reserves in the soil. The pods of snail are more vulnerable than those of barrel medics.

Medics and bloat

Annual medics will cause bloat in sheep and cattle, although sheep are less affected than cattle and snail medics may be less of a problem than barrel and naturalised medics. Bloat is not a big issue, but in wet winters following dry summers when dry grass is limiting, problems will occur.

Bloat can be managed in smaller paddocks by:

  • using bloat mixtures applied to water troughs
  • providing access to dry grass or hay
  • bloat capsules can be used for valuable stock.

When medic pastures are lush, stock are best removed to alternative sources of grazing.