Trifolium ambiguum M. Bieb.
Caucasian clover, kura clover, pellett clover, honey clover.
Dr. John Frame
Prostrate perennial with trifoliate, glabrous leaves; leaflets lanceolate to ovate with dentate margins, glaucous undersides and commonly with white V-shaped markings; petioles glabrous or slightly pubescent; membranous stipules with distinct veins; prostrate to erect stems, 0.5 m, branching from plant crown. Tap-rooted with numerous lateral roots, spreading via rhizomes. High ratio of underground:aerial biomass (Daly and Mason, l987). Mellifluous inflorescences are terminal and capitate with up to 175 white florets. Self-incompatible, pollinated by bees. Obovoid flattened seed pods usually contain two light brown to brown seeds.
Native to Asia Minor (countries around the eastern shores of the Black Sea) and Caucasus region. Introduced to southern Australasia, North America (north-east and north-central) and increasingly in recent times to other countries.
Adapted to a range of soil and climatic conditions from ill-drained lowlands to alpine-type meadows at 3200 m a.s.l. (Speer and Allinson, l985; Taylor and Smith, l998). Rhizomatous growth habit and large root mass make it resistant to heat, drought and winter cold. Persistent under grazing once fully established, but has a slow establishment phase. Poor seed producer (Widdup et al., l996).
Season of growth
Highest yielding in late spring and summer.
Established swards are highly tolerant. Has early autumn dormancy.
Established swards are highly tolerant; establishing swards less tolerant.
Tolerance of flooding
Winter-wet soils adversely affect persistence (Yates, l993).
Can thrive on a range of soil fertility environments - and though fairly productive on infertile soils it responds to liming (Barnard and Folscher, l988) and to P fertilization (Davis, l99l; Virgona and Dear, l996). A soil pH range of 6.0 to 7.4 is cited by PLANTS database (2000).
Seed should be inoculated with an effective strain of Rhizobium for successful establishment and subsequent performance (Lowther and Patrick, l992; Patrick and Lowther, l995). Ineffective nodulation due to lack of rhizobial inoculation has hampered widespread uptake of caucasian clover in the past. Ploidy-specific strains of rhizobia have been developed (Pryor et al., 1998).
Ability to spread naturally
The main perennating organs are rhizomes which allow the plant to spread up to 30 cm per year (Albrecht, 1998) and develop. Shed seed from plants in ungrazed patches can provide some regeneration but an open sward canopy is necessary for germination and development.
Land preparation for establishment
Well cultivated, uniform and firm seed bed required for good results. Ploidy-specific strains of rhizobia have been developed (Pryor et al., l998).
Can be conventionally broadcast or drilled shallowly in well-prepared seed beds. Strip-seeding into an existing grass sward has proved successful (Moorhead et al., l994).
Sowing depth and soil cover
Sown at 10-15 mm depth with a firm soil cover.
Sowing time and seed rate
Spring is best but late summer is possible provided there is adequate moisture and sufficient time for the clover seedlings to develop well before winter since seedlings are frost-sensitive (Caradus, l995). Seed rate 6-12 kg/ha (Strachan et al., l994; Albrecht, 2000) but low rates best when grown for seed production.
Number of seeds per kg
Variable; 551 000 for cv. Rhizo cited by PLANTS database (2000); 662 000 (diploid), 583 000 (tetraploid) and 336 000 (hexaploid) reported by Kannenberg and Elliott (l962).
Percentage hard seeds
Usually a high percentage.
Seed treatment before sowing
For commercial sowing rates, no treatment is usually necessary, but at low seeding rates for seed production purposes, scarification is necessary if the seed lot has a high proportion of hard seed (Moorhead et al., l994).
Compatibility with grasses and legumes
Information is sparse but non-aggressive grasses are likely to make the best companions. Once established, has excellent compatibility with all the grass species commonly used in northern USA for pasture and hay (K.A. Albrecht, pers. comm.) Root and rhizome growth of caucasian clover are restricted by dense sowings of companion grass (Hill and Mulcahy, l995).
Ability to compete with weeds
Poor during early establishment phase but improves with time after underground biomass has developed. If present, weeds must be controlled by cultural means or by clover-safe herbicides to improve establishment success.
Vigour of growth and growth rhythm
Slow establishment phase. Can grow vigorously in late spring and summer when fully established, particularly once its root and rhizome biomass has become well developed. Good initial seedling establishment and fertilizer application are important for subsequent growth vigour and yield (Lowther et al., l998).
Reported to be high (PLANTS database, 2000) but requires successful root nodulation by effective rhizobia. Caucasian clover was in a top group along with such species as white, red and crimson clovers from nearly 50 Fabaceae species assessed for nitrogen-fixing ability (Pelikan and Hofbauer, l999).
Response to defoliation
Tolerant of a range of cutting and sheep grazing regimes (Taylor and Smith, l998).
Caucasian clover tolerates close, frequent defoliation (21-day rest period) but is more productive with longer rest periods (Peterson et al., 1994; Kim, 1996; Kim et al., 2001).
Self-incompatible, cross-pollinated mainly by honey bees. Has diploid (2n = 2x = 16), tetraploid, (2n = 4x = 32) and hexaploid (2n = 6x = 48) forms.
Improved seedling vigour. More rapid establishment phase. Better regrowth after defoliation. Higher seed yields. Hybridisation with white clover has been a part of several breeding programmes but a commercial cultivar has yet to be released.
Dry matter yields
Attained 5.00-6.50 t/ha in northern USA (Taylor and Smith, l998) but much lower yields (1.04-1.96 t/ha) in south-eastern Australian high country, with a hexaploid cultivar outyielding a diploid cultivar (Virgona and Dear, l996); other work there has shown superior yields from hexaploids and diploids compared with tetraploids (Dear and Zorin, l985). Sixth-year yields from cut plots in New Zealand high country reached 3 t/ha with maintenance fertilization which was 3-7 times those when fertilizer had only been applied at sowing (Lowther et al., l998).
Highly acceptable forage for grazing especially when leafy. Has some cyanogenic potential but less than for white clover (Hill et al., l995).
Risk of bloat when grazing (but conventional prevention methods are available).
High nutritive value particularly on account of a high leaf:stem ratio (Sheaffer et al., l992). Caucasian clover had higher digestibility than forage legumes such as lucerne, red clover, birdsfoot trefoil and crown vetch (Allinson et al., l985; Sheaffer and Marten, l99l). Forage protein-rich.
Yields up to 289 kg/ha have been achieved in Oregon, USA (Steiner, l992).
Australian cultivars are diploids Summit and Alpine and hexaploids Treeline and Monaro, all suited to high country conditions; also hexaploid Prairie suited to low country. Other hexaploid selections are Rhizo (USA) and Endura (New Zealand). Further cultivars can be expected from breeding programmes in several countries, given the increased interest in the positive characteristics of caucasian clover. White clover x caucasian clover hybrids can also be expected in the near future.
May suffer from powdery mildew (Erysiphe trifolii) (Taylor and Smith, l998).
Resistant to most viruses. Alfalfa mosaic virus and soybean mosaic virus have been found but the impact on the plant is not yet known (K.A. Albrecht and C.R. Grau, pers.comm.).
Susceptible to root-lesion nematode (Pratylenchus penetrans) (Thies et al., l995). Roots can be attacked by larvae of the grass grub (Costelytra zealandica) in New Zealand (Dymock et al., l989). Potato leafhopper (Empoasca fabae) causes purple colouring in leaves and stunting of plants (K.A. Albrecht, pers.comm.).
Resistant to drought and winter cold. Persistent via its rhizomatous growth habit. Resistant to pests and diseases. Forage highly acceptable to livestock and of high feeding value. Excellent plant for honey production.
Poor seedling vigour. Slow to establish fully. Slow recovery growth after harvesting. Risk of bloat. Poor seed producer.
Daily liveweight gains for lambs were circa 200 g for caucasian clover, birdsfoot trefoil and a mixture of both (Sheaffer et al., l992), while steers gained 1.3 kg/day on a grass/caucasian clover pasture (K.A. Albrecht, pers.comm.).
Albrecht K.A. (1998); Albrecht K.A. (2000); Allinson D.W. et al.(l985); Barnard R.O. and Folscher W.J. (l988); Caradus J.R. (l995); Daly G.T. and Mason C.R. (l987); Davis M.R. (l99l); Dear B.S. and Zorin M. (l985); Dymock J.J. et al. (l989); Hill M.J. and Mulcahy C. (l995); Hill M.J. et al.(l995); Kannenberg L.W. and Elliott F.C.(l962); Kim B.W.(1996); Kim B.W. et al.(2001); Lowther W.L. and Patrick H.N. (l992); Lowther W.L. et al. (l998); Moorhead A.J.E. et al.( l994); Patrick H.N. and Lowther W.L. (l995); Peterson P.R. et al.(1994); Pelikan J. and Hofbauer J. (l999); Pryor H.N. et al.(1998); Sheaffer C.C. and Marten G.C. (l99l); Sheaffer C.C. et al. (l992); Steiner J.J. (l992); Strachan D.E. et al.(l994); Thies J.A. et al.(l995); Virgona J.M. and Dear B.S. (l996); Widdup K.H. et al.(l996); Yates J.J. (1993)