Trifolium hirtum All.
|
Trifolium hirtum All.
|
  |
Leguminoseae Common names Rose clover |
Author:
Dr. John Frame
|
|
Description Pubescent annual, decumbent to erect growth habit. Leaflets obovate, pale green, usually marked with pale crescents bordered by brownish-red lines, though cultivars differ in form and position of markings. Stipules lanceolate to ovate. Deep rooting to circa 2 m. Inflorescences terminal, globose racemes with 20-40 sessile, pinkish-red florets. Pods contain a single rounded yellow seed. Distribution Native to Mediterranean countries and Asia Minor. Adapted to infertile soils and dry climates, 350-900 mm annual rainfall. Grown on dry rangelands of California and Western Australia, but also parts of central-south USA. Characteristics Suited to a range of infertile soil types though not to poorly-drained soils; tolerates droughty soils better than other annual clovers; intolerant of soil salinity. Moderately shade tolerant. Generally nil fire tolerance but cvs Hykon and Wilton have medium fire tolerance (PLANTS database, 2000). Season of growth Autumn to spring. Temperature for growth For good germination in autumn minimum daily temperatures of 150C or less necessary (Evers, l99l). Frost tolerance Can tolerate temperatures considerably below freezing point. Drought tolerance Moderately tolerant and more so than subterranean clover (T. subterraneum). Tolerance of flooding Intolerant. Soil requirements Soil pH range of 5.0 (A.Loi, pers. comm.) to 7.5 (PLANTS database, 2000). Subject to Fe chlorosis on strongly alkaline soil and to Al toxicity on strongly acid soil (Hoveland and Evers, l995). Responsive to P fertilization on soils of low P status. Rhizobial relationships Seed inoculation with effective Rhizobium strain required when sown onto land without previous history of growing rose, crimson or subterranean clover (Love, l985). Ability to spread naturally Its high proportion of hard seed and slow rate of seed softening gives it good self-regeneration capability from the soil seed bank following rainfall after summer drought. Summer grazing of dried standing forage is beneficial to seed shedding and incorporation into the soil; however sheep can easily graze the mature seed heads even after they have shattered onto the ground. Having relatively large-sized seeds, few of which survive passage through the animal, the seed bank in the soil can easily be run down resulting in poor stand persistence over time. In Western Australia, overgrazing during spring and summer, the upright growth habit of the plant and the high level of hard seeds with low to moderate levels of seed softening in rose clover cultivars in the past (and the lack of promotion) were factors causing unreliable regeneration. New cultivars are now being developed that have more suitable rates of seed softening and also better knowledge is available of the stand management required. Land preparation for establishment Well-cultivated, uniform and firm seed bed required for good results when first establishing. Sowing methods Can be drilled into, or broadcast onto, a conventionally-prepared seed bed. Sowing depth and cover Shallow sowing at 6-12 mm depth with a firm soil cover. Sowing time and rate Drillled at 5 kg/ha or broadcast at l0-l5 kg/ha in autumn (Love, l985). Number of seeds per kg 245 000 to 390 000. Percentage hard seeds Very high, circa 90% ; can retain viability in the soil for several years. Nutrient requirement Responds to improved soil fertility, particularly to P application. Compatibility with other grasses and legumes Commonly sown in mixture with crimson clover (T. incarnatum) and subterranean clover (T. subterraneum) in order to exploit different levels of soil fertility of the area sown. Seedling vigour Poor to moderate. Based on seedling development, namely, leaves, nodulation, shoot weight, root weight, root length and LAI, rose clover (and arrowleaf clover) had the lowest values in comparison with crimson clover (highest values) and subterranean clover (intermediate value) (Evers, 1999). Vigour of growth and growth rhythm Rapid growth rate but moderate regrowth rate after defoliation. Nitrogen-fixing ability Moderate. Response to defoliation Cannot withstand frequent, severe defoliation. Grazing management Has to be such that a balance is struck between utilizing forage efficiently yet not so severely that seed production – the basis for annual pasture regeneration – is compromised. Rotational grazing system best. Not suited to continuous, heavy sheep grazing (Love, l985). Grazing can continue during dry summer / autumn period, a practice which assists seed burial by stock trampling. Breeding system Chromosome number 2n = 2x = 10. Breeding objectives More rapid seed softening. Improved grazing tolerance. Higher herbage yields. Dry matter yields Attained 4-5 t/ha in a 450 mm annual rainfall region of south-western Australia (A. Loi, pers.comm.). Acceptability High acceptability to livestock, even of the dried-out forage in summer. Feeding value High. Anti-quality factors Negligible risk of bloat (PLANTS database, 2000). Seed harvesting methods A rasp-bar combine is advisable since the seeds are held tightly by the calyces (Hoveland and Evers, l995). Seed yields 300-500 kg/ha in California (Love, l985); 500-600 kg/ha in a 450 mm rainfall region in south-western Australia (A. Loi, pers.comm.). Cultivars Mostly of Australian origin and with different times of maturity. Include early-flowering Hykon and Kondinin and later-flowering Wilton and Overton R-18. Main attributes N-fixing, protein-rich species adapted to infertile, dry environments. High self-regeneration capacity because of hard-seed production. Highly acceptable forage to livestock. Freedom from diseases and pests. Main shortcomings Sward density and forage yield variable from year to year partly because of dependence on amount of seed in soil seed bank. Poor to moderate seedling vigour. Links
Main references Plants Database 2000; Hoveland C.S. and Evers G.W. (l995); Love R.M. (l985) Other references |