Trifolium michelianum Savi
B.S. Dear, A.D. Craig, G.A. Sandral
NSW Agriculture Wagga Wagga Agricultural Institute
Struan Research Center
A winter growing annual, herbaceous, self-regenerating legume in Mediterranean climates. Habit prostrate as a single plant, becoming semi-erect in dense swards. Stems predominantly green with occasional red coloration, glabrous, hollow when elongated. Leaves trifoliate, alternate, green, glabrous. Margins weakly-strongly serrate. Leaf markers vary in colour, position and degrees of distinctiveness, incidence of anthocyanin pigmentation very low. Petioles light green, glabrous, hollow when elongated. Stipules entire, 5-15 mm long, green-red in colour. Inflorescence umbellate, 20-30 mm in diameter. Peduncles predominantly green with occasional red coloration, glabrous. Pedicels bracteate, green-red in colour. Number of florets variable, typically 35-55 per inflorescence. Corolla white-pink, 9-13 mm long, standard terminating in a faint pink tip. Pink flowers typically in the outer whorl of the inflorescence. Pink coloration strengthens with maturity prior to becoming light-brown in the mature head. Calyx green, 6 mm long, 5 lobes, uneven in length, 2-3 times longer than the tube. Seeds 1-2 mm, ovoid-oblong, colour variable, including olive green, yellow, light brown, dark brown to black. Seed shatters readily from the head.
Season of growth. Autumn to spring. Senesces over summer. Germinates in autumn with main growth produced in late winter-spring. Life cycle adapted to avoid summer drought.
Adapted to regions with predominantly Mediterranean or temperate climates, hot dry summers, moist, cool winters.
There is no experimental data on the optimum temperature for growth but field observations suggest growth is most rapid at 20-25°C. Balansa clover is tolerant of frosts in winter (-60C).
Require annual rainfall between 350 and 750 mm. Swards mature and die in late spring but regenerate from seed reserves in autumn following the summer drought. Balansa clover is tolerant of extensive periods of waterlogging once established but young seedlings are sensitive to prolonged submersion. Balansa clover has moderate tolerance of salinity. Seedlings have similar tolerance to subterranean clover but adult plants are more tolerant (Rogers and Noble 1991).
Suited to a wide range of soil types but prefers mildly acid to mildly alkaline soils but is known to grow in soils with a pH range (CaCl2) 4.5-8.0. It has been grown successfully on soils ranging from heavy clays through to red brown earths, alluvial soils and solodised solentz. It prefers soils of moderate high fertility and is not suited to deep infertile sands. Balansa clover is rated as moderately susceptible to high soil aluminium levels, being more tolerant than Persian clover (T. resupinatum) but less tolerant than subterranean clover (T. subterraneum) and white clover (T. repens).
T. michelianum var michelianum has a natural distribution throughout southern Europe from Spain to Turkey. Zohary and Heler (1984) state that T. michelianum var balansae and T. balansae are synonymous. The common name balansa clover is used to refer to all subspecies of T. michelianum. Balansa clover (var michelianum) is now widely grown throughout southern and eastern Australia.
A well cultivated , uniform and firm seed bed is required when first establishing balansa clover. Good weed control at establishment is also very important.
Nutrient requirements. Phosphorus requirements are similar or slightly higher than for subterranean clover. Liming of acid soils will enhance establishment and herbage yields. Molybdenum may be necessary to promote nitrogen fixation in acid soils.
Compatibility with other grasses and legumes. It can be grown in mixtures with other annual and perennial legumes and annual grasses. In Australia it is successfully grown in mixtures with subterranean clover and lucerne (Medicago sativa L.) and ryegrass (Lolium multiflorum and L. rigidum) but good grazing management is required to promote re-establishment in autumn.
Ability to compete with weeds. Small seedlings are sensitive to weed competition. Grazing established swards in autumn, soon after emergence, assists in reducing weed competition.
Tolerance of herbicides. Seedling response (4-5 leaf stage) to broadleaf herbicides varies from tolerant to highly sensitive. Herbicides found to suppress herbage yield by less than 20% include Flumetsulam, Imazethapyr, 2,4 DB, and Diflufenican. Metosulam and herbicides containing bromoxynil are likely to cause yield losses in excess of 80%.
Seedling vigour. Low relative to larger seeded legumes.
Vigour of growth and growth rhythm. Initial growth in autumn is slow with growth rates increasing in early spring. Winter yields are substantially increased if the time of establishment in autumn is advanced either through irrigation or early autumn rainfall. Swards dry off in late spring/early summer.
Nitrogen-fixing ability. Has not been quantified but experience suggests that balansa clover is capable of forming an effective symbiosis with a number of strains of Rhizobium leguminosarum bv. trifolii.
Response to defoliation. Tolerant to both continuous and rotational grazing but persistence is better under the former. It remains relatively prostrate when continuously grazed and is very tolerant to regular defoliation while young. Left ungrazed it will grow up to 1 metre tall in spring, the stems collapsing and growing horizontally. It does not recover well from a late cut or grazing when stems are large and the plants tall and flowering. Very little seed will be produced if mature flowering stands are hard grazed.
Grazing management. Once established, balansa clover should be grazed after emergence to control weed competition. Stock should be removed prior to flowering in seed crops but may remain at a reduced stocking rate in pastures and still permit sufficient seed set for regeneration the following year. Dry plant residues need to be hard grazed over summer to assist in the breakdown of hard seed. Capable of regenerating reliably for a number of years under appropriate management.
Rhizobial relationships. Rhizobial nitrogen fixation in the root nodules is by strains of Rhizobium leguminosarum bv. trifolii. Seed must be inoculated with rhizobium when sown into ground not containing an effective rhizobia or where rhizobium survival is poor due to soil acidity. Nodulates effectively with a number of rhizobial strains although WSM 409 is the currently recommended strain.
Ability to spread naturally. Balansa clover spreads readily by seed. A high proportion of seed consumed by stock passes through the rumen undigested and will be spread in dung. Balansa clover seed harvested in late cut hay crops is also likely to be spread when fed out.
Sowing methods. Because of the very small seed size it is essential to sow the seed very shallow, no deeper than 7 mm, into a well prepared seed bed. Can also be established by dropping seed onto the surface (broadcasting) or by direct drilling if environmental conditions are suitable and competition from other species is controlled. Significant seed losses due to ant theft can occur with surface sowings. Balansa clover has also been successfully established by direct drilling into old lucerne stands and aerially sown into rice stubble and well grazed grasslands.
Sowing time and rate. Sown in autumn when probability of favourable soil moisture is high. Sowing rates of 2-5 kg/ha are used to establish new pure stands of balansa clover. Rates of 0.5-1.0 kg/ha are sufficient when sown in a mixture with other species. Higher sowing rates (5 kg/ha) are used when it is sown as a one year forage crop.
Number of seeds per kg. Seed is very small averaging about 980,000 1.2 million seeds/kg.
Percentage hard seeds. Approximately 97% is hard (non germinable) at maturity with the hard seed level falling to about 50% by mid April if left in the paddock.
Seed treatment before sowing. Seed harvested on farm will have a very high proportion of hard seed which must be scarified before use to achieve a good seedling germination and establishment. Certified seed purchased commercially will have been scarified to ensure a high percentage (>65%) of soft germinable seed.
Breeding system. The species is a strongly outcrossing diploid with 2n=16 chromosomes.
Breeding objectives. The major breeding objectives have been to select for high herbage yield and to extend the range of maturities by selecting cultivars with either a shorter or longer time to flower. Present efforts to improve the species are being achieved by single plant selection techniques. Improved winter vigour and earth mite tolerance remain as major selection objectives.
Seed harvesting. Most seed crops are direct headed. Seed shatters readily from the head, particularly with wind, rain or hail. Windrowing the seed crop promotes even ripening and is recommended to maximise seed yields. Seed is considered ready for windrowing when at least 70% of the seed in the head is mature.
Seed yields. Seed yields of up to 1000 kg/ha have been achieved in seed crops but yields of 200-300 kg are typical of grazed pastures.
Seed quality standards. For certification in Australia, the seed must contain a minimum of 65 % germinable seeds. Minimum pure seed by mass is 98%, with maximum other seeds by mass being 1% and permitting 1% inert matter.
Cultivars. Three cultivars of balansa clover (cvs. Frontier, Paradana and Bolta) have been developed in Australia which differ mostly in their time to flower. These are believed to be the only commercial cultivars of balansa clover. All three cultivars are derived from accessions introduced from Turkey. Frontier is the earliest flowering cultivar, reaching full flower in about 100-115 days after a mid-May sowing. Being the earliest flowering it is best adapted to shorter growing seasons (350-500 mm annual rainfall) and will mature earlier in spring than the other cultivars. The cultivar Paradana (Craig and Beale 1985) is of mid-season maturity (115-130 days to flower) having a mean flowering time 2-3 weeks later than Frontier and requiring 500-600 mm annual rainfall. The latest flowering cultivar, Bolta (Craig 1998), flowers about 10 days later than Paradana and is suited to higher rainfall districts (>600 mm) with a longer growing season. All cultivars have high levels of hard seed at maturity. The three cultivars may be distinguished from each other through their leaf markings. Bolta and Frontier are protected by Australian Plant Breeders Rights.
Developed as forage for livestock and as a nitrogen source for crops. Suitable for standing feed, hay or silage production.
Dry matter yields. . Herbage yields of 5-6 tonnes /ha are achievable under dryland conditions and 7-8 tonnes/ha under irrigation. Higher yields are achieved with earlier sowing or emergence or by using later maturing cultivars under suitable conditions.
Suitability for hay and silage. The rapid growth of balansa in spring, its erect growth habit, high level of tolerance to clover scorch disease and high digestibility make it ideally suited to silage and haymaking. Well established balansa pastures cut for hay should recover the following year from hard seed reserves set in previous years. New balansa clover pastures should not be cut for hay if they are required to regenerate. Balansa clover hay typically has a digestibility of between 76% and 82% with a crude protein of 14% to 18%. The thick stems are as digestible as the leaves.
Anti-quality factors. Balansa clover has low levels of the isoflavone formononetin. These levels are not considered sufficient to cause animal reproductive disorders. The isoflavones genistein and biochanin A have not been detected. As with many legumes, balansa clover can cause bloat in livestock, particularly in cattle.
Suitability for honey production. Attractive to bees with pollen containing 27-29% protein (dry weight). Produces a light coloured honey.
Main attributes. Broad environmental adaptation, tolerance of waterlogging and salinity, rapid spring growth.
Main shortcomings. Lack of seedling vigour and slow autumn growth. Susceptibility to RLEM during the seedling stage further restricts its performance.
Acceptability to stock. Highly palatable to stock both as green feed, hay and silage.
Feeding value. The dry matter digestibility of balansa clover is similar to subterranean clover during autumn and winter (70-80% in-vitro) but falls rapidly in spring as the herbage matures to about 60% by December. Nitrogen content of green herbage ranges from 2.9% to 3.9% (Kelly and Mason 1986).
Diseases. Accessions vary in their susceptibility to clover scorch disease (Kabatiella caulivora) from tolerant to highly susceptible (Snowball 1993) but all three cultivars are rated as tolerant. Balansa clover is susceptible to Pythium spp. during the seedling stage. Commercial cultivars display good field tolerance to leaf and stem rust.
Viruses. Known to be susceptible to a range of common viruses including clover yellow vein virus, subterranean clover stunt virus and alfalfa mosaic virus, although commercial losses appear to be relatively minor.
Pests. Tolerance of accessions to redlegged earth mite (RLEM) (Halotydeus destructor) during the seedling stage varies from moderately tolerant to highly susceptible (Snowball 1993). The three cultivars are rated as susceptible. Swards must be carefully monitored and sprayed early, if RLEM are present, to ensure good establishment. This is especially important in the first year. The tolerance of plants to RLEM increases as plants mature. Balansa clover is also susceptible to lucerne flea (Sminthurus viridis). Balansa clover is reported to have good field tolerance to bluegreen aphid (Acyrthosiphon kondoi), cowpea aphid (Aphis craccivora) and spotted alfalfa aphid (Therioaphis trifolii), but is susceptible to all three species under glasshouse conditions.