Part A - Subterranean clover in NSW - identification and use

Introduction

Subterranean clover is the most important annual pasture legume sown in southern Australia. It originated in the Mediterranean region, parts of western Europe, southern England and Ireland.

Subterranean clover (sub clover) was accidentally brought to Australia in hay, straw and pasture seed, probably as early as the 1830s, and was spread along transport routes, in stock camps and on town commons throughout southern Australia.

The potential of sub clover to provide nutritious feed for livestock and improve soil fertility was first recognised early this century by AW Howard in South Australia. During the 1950s, sub clover was widely adopted by farmers as the basis for improved pastures and leys in southern Australia. It is now grown on over 7.7 million hectares of agricultural land in New South Wales, from areas receiving as little as 375 mm average annual rainfall in the south of the state, to those receiving more than 1000 mm in the north. In NSW, sub clover species are grown on the Northern, Central and Southern Tablelands and Slopes, the Riverina and in coastal areas.

In recent years the density and productivity of older sub clover varieties has declined as a result of:

disease (phytophthora root rot) - see Diseases of sub clover (Part B);
pests (such as bluegreen aphid and redlegged earth mite) - see Insect pests of sub clover (Part C);
insufficient applications of superphosphate.

But the release of new varieties and revised recommendations for establishing and managing sub clover pastures will now allow most farmers to meet the challenge of pasture redevelopment.

Subspecies and varieties

Sub clover has been divided into three subspecies, each of which is best suited to particular soil and environmental conditions:

Trifolium subterraneum subsp. subterraneum, the most commonly used species, does best on well-drained, slightly acid soils, and is represented by the cultivars:
Trifolium subterraneum subsp. yanninicum, also an important subspecies, does well on poorly drained land and areas subject to intermittent waterlogging. It is represented by the varieties:
The seed of T. yanninicum varieties is a characteristic cream to light brown colour. Unlike many T. subterraneum varieties, the plant is not hairy, and the calyx lobes (bracts at base of flower) are elongated.
Trifolium subterraneum subsp. brachycalycinum, the third subspecies, is currently represented in Australia by the varieties:
These varieties are best adapted to neutral to alkaline, cracking or self-mulching soils but will grow on mildly acidic soils. Unlike other sub clovers, T. brachycalycinum has little ability to bury its seed, but its long, twining peduncle (flower stalk) seeks out cracks in the soil and hides the burr in these.

The considerable variation within the three subspecies largely accounts for the wide distribution of sub clover. Hundreds of strains have been collected in Australia and overseas, but only a handful of these have been used commercially. Preliminary evaluation and long-term storage of these strains, which constitute a unique genetic resource, are undertaken by the National Annual Pasture Legume Improvement Program (NAPLIP). NSW Agriculture cooperates closely with this national program, to test new sub clovers and conduct supporting research.

Currently 35 commercial varieties of sub clover are registered but half of these are no longer in widespread use. Varieties differ in their appearance and in many important agronomic characteristics, such as maturity, hardseededness and disease resistance. For particular environments, specific varieties are favoured because their characteristics make them better adapted to those situations. The relative importance of these characteristics can change from district to district and even from paddock to paddock.

For further information, see:

Seed yield

A pure stand of sub clover under ideal growing conditions has the potential to set up to 1500 kg/ha seed. Typically sub clover seed crops yield 600–1000 kg seed/ha, while clover growing in grassy pasture will set between 200 and 500 kg seed/ha.

Clover seed yields are maximised by:

controlling weeds;
ensuring optimum nutrition and soil pH;
limiting moisture stress during seed filling, either by irrigation or by growing varieties whose maturity matches the growing season of the district.

To promote seed yield once flowering commences, either remove stock or greatly reduce the stocking rate.

Seed marketing

Most new cultivars are now protected under Plant Breeder’s Rights (PBR) legislation. This gives the licensee rights over the propagation and sale of seed. Unauthorised commercial propagation and sale of protected varieties is an infringement of the PBR Act. (Further information is available from Plant Breeder’s Rights.)

Growing sub clover under irrigation

Irrigation can be used to extend the growing season of subterranean clover:

Sub clover can be germinated earlier (early March) to increase the supply of autumn–winter feed.
It can also be irrigated in late spring to extend the growing season into late November to early December, provided later maturing varieties are grown.

While all varieties are suited to irrigation, yanninicum varieties should be used as part of the mix where waterlogging is likely. Similarly, varieties with good resistance to root diseases should be sown, as these diseases can be more severe where germination occurs in warm soils in early autumn.

For detailed management guidelines on irrigated sub clover, refer to NSW Agriculture booklet Irrigated subcheck recommendations (1996).

Pasture mixes

Varietal mixtures

Where spring rainfall is variable and there is a strong chance of false autumn breaks, growers can ensure greater persistence of sub clover swards by mixing shorter-season, harder seeded varieties with later maturing, softer seeded varieties.

In districts with a high rainfall, the short-season varieties are less productive in spring than the longer-season varieties, as short-season varieties set seed and die early in spring.

It can also be useful to mix varieties with different characteristics when the soil type or drainage varies within a paddock. For example:

In paddocks with variable drainage:
Including a yanninicum variety, such as Riverina or Gosse, with a variety better suited to the well-drained portions of the paddock will result in a better clover sward.
On the Northern Slopes where a range of soil types can occur within a paddock:
Seaton Park produces well on better drained areas, and Clare is superior on heavier soils within the same paddock.

For further information, see:

Species mixtures

Sub clover and lucerne make a valuable pasture mix that increases the period of feed availability and results in better livestock growth. Shorter-season sub clovers should be included in a lucerne / sub clover pasture, as moisture competition from the lucerne may not allow mid-season or later varieties to persist satisfactorily.
Mixtures of sub clover and annual medic can be worthwhile in some western areas where soils vary from those that favour medics to those in which sub clover grows best. Often these boundaries are not clearly defined, so a mixture of species is a practical option.
Similarly, sub clover can be grown with serradella where there are highly acid patches.
Adding balansa clover to sub clover can give good results where parts of the paddock are waterlogged.
Mixing white clover and sub clover is generally not successful due to strong competition from white clover in the first couple of years. Sowing white clover separately in wetter areas and sub clover in the better drained parts of the paddock is a preferred option.
Sub clover is also grown in mixtures with perennial grasses such as phalaris, cocksfoot or austrodanthonia (wallaby grass). To ensure good clover regeneration, the grass needs to be well grazed in late summer to remove residues prior to autumn rains. Grass residues have been shown to reduce the germination and growth of clover seedlings.

Further information

For further information on subterranean clover, see the other sections of this Agfact:

PASTURE IMPROVEMENT CAUTIONS

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

Current conservation legislation may restrict some pasture improvement practices where existing pasture contains native species. Inquire through your office of the Department of Infrastructure, Planning and Natural Resources for further details.