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Trifolium vesiculosum Savi |
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Leguminoseae Common names Arrowleaf clover. |
Author:
Dr. John Frame
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Description Glabrous annual, semi-erect growing with a crown rosette of branching, hollow stems, up to 1.5 cm. Leaflets arrowhead- or spearhead-shaped at stem elongation and flowering stage, but obovate at earlier stages of development, with pronounced veination and commonly with white, light green or red, V-shaped leaf marks; white pointed stipules at base of leaf petioles. Deep-rooted inflorescences conical, 5 cm or more. Florets, l50-l70 in number are initially white but become purplish. Flowering extends over 1-2 months. Cross-pollinated by bumble bees and honey bees. Two to three seeds, brown in colour, produced per seed pod, which is protected by inflated calyx at maturity. Has smaller seeds than crimson (T. incarnatum), subterranean (T. subterraneum) or rose (T. hirtum) clovers. Distribution Native to southern and central Europe where grown as winter annual for forage. In excess of 0.5 M ha grown in south-east USA for cool-season growth (Hoveland and Evers, l995) making it the most important annual clover in the USA (circa 2.5 times the hectarage of crimson clover, the next most important annual there). Characteristics Thrives on fertile, well-drained soils but not on acid, ill-drained soils of low fertility, saline or alkaline soils. Exhibits symptoms of Fe-deficiency chlorosis when grown on calcareous soils (Ocumpaugh et al., l99l). Moderately vigorous seedling growth. Not tolerant of shade. Season of growth Winter and spring but extending to early summer. Frost tolerance Poor tolerance (less winter hardy than crimson clover). Was one of the most frost sensitive of 13 Trifolium species artificially frosted at -4, -8, -12 and -160C (Caradus, l995). Drought tolerance Moderate tolerance. Tolerance of flooding Intolerant Soil requirements Target soil pH 6 to 7.0 (PLANTS database, 2000). Benefits from high soil fertility. Grows well on deep, infertile sandy soils particularly with a perched water table at 1-2 m. Rhizobium relationships Rhizobial inoculation of seed necessary prior to sowing onto land without previous history of growing arrowleaf clover. Improved strains of Rhizobium commercially available, e.g. in Australia Ability to spread naturally Good ability to self-reseed because of high production of hard seed. A proportion of seed ingested by sheep can pass undamaged through the gut. Land preparation for establishment Well-cultivated, uniform and firm seed bed required for best results. Direct drilling (sod seeding) most successful on swards with low-density vegetation and when there is adequate soil moisture. Sowing methods Can be conventionally broadcast or drilled in well-prepared seed beds. Can also be direct drilled (sod seeded) following close defoliation of the sward, into perennial warm-season grass swards, e.g. bahia grass, Bermuda grass, in south-east USA (Overman et al., l992) or natural pastures in southern Brazil (Vidor and Jacques, l998). Sowing depth and soil cover The optimum sowing depth is 10-20 mm with a firm soil cover. Sowing time and seed rate Sown in late summer to autumn when pure-sown and up to early winter for oversowing into warm-season grass swards for grazing. The seed should be sown early enough for sufficient seedling development to withstand winter conditions but cool temperatures of circa 150C or less are necessary for good germination (Evers, l980). Seed rate 7-11 kg/ha of scarified seed (Miller and Wells, l985). Number of seeds per kg Circa 880 000. Percentage hard seed Usually high. Compatibility with grasses and legumes Compatible with grasses such as bahia grass (Paspalum notatum) and Bermuda grass (Cynodon dactylon). Seedling vigour Low to moderate. Based on seedling development, namely, leaves, nodules, shoot weight, root weight, root length and LAI, arrowleaf (and rose clover) had the lowest values in comparison with crimson clover (highest values) and subterranean clover (intermediate) (Evers, l999). Vigour of growth and growth rhythm Strong vigour once established. Vigorous winter-spring growth (Pedersen and Ball, l99l) extending into summer when late-maturing cultivars used. Nitrogen-fixing ability Reported to be high. Response to defoliation Close grazing should be avoided in winter so as not to affect spring growth or seed production adversely. Grazing management Has to be such that a balance is struck between utilizing forage efficiently yet not so severely that seed production – the basis of regeneration – is compromised. Timing of cessation of grazing in spring important in relation to obtaining a seed crop; sheep will graze the dry stubble left during late summer and autumn. Breeding system Cross-pollinated by bumble bees and honey bees. Chromosome number 2n = 2x = 16. Breeding objectives Develop cultivars for growing seasons of different lengths (determined by moisture availability); improvement of grazing tolerance; more rapid seed softening. Dry matter yields Potential for high yields when growing conditions are good. Up to 9.4 t/ha achieved in Western Australia (Wiley and Maughan, 1993). Suitability for hay and silage Suitable for hay and silage. Acceptability Highly acceptable forage for grazing, silage or hay. Feeding value Protein-rich especially at leafy growth stage. Digestibility declines with maturity and associated increase in stem:leaf ratio. Seed harvesting methods Successfully harvested with open-front headers when majority of seeds mature (Wiley et al., 1993). Seed yields In specialist seed-growing areas in Oregon, USA, 670-900 kg/ha achieved, but yields are much lower in south-east (l00-400 kg/ha). Cultivars The main USA cultivars are Amclo (early maturing), Yuchi (intermediate maturing) and Meechee (late maturing). Australian cultivars include Cefalu (early maturing), Seelu (late maturing), Zulu (late maturing, and Arrotas (very late maturing). Diseases Clover rot (Sclerotinia trifoliorum) can occur in dense swards in wet winters. Risk of Phytophthora foot rot (Phytophthora megasperma) following virus infections. Viruses Bean yellow mosaic and peanut stunt viruses can be a serious problem. Subterranean clover red leaf virus has been isolated from arrowleaf clover in Western Australia. Pests Seedlings in oversown grass swards may be attacked by the striped field cricket (Nemobius fasciatus). Plants are susceptible to root knot nematodes (Meloidogyne spp.) (Miller and Wells, l985). In Australia, the red-legged earth mite (Halotydens destructor) can reduce seedling numbers at establishment but established swards are more resistant (Wiley et al., 1993). Major attributes High yield (particularly with late maturing cultivars). Good forage acceptability and feeding value. High proportion of hard seed produced conferring good self-reseeding characteristic. Relatively deep rooted with medium to late flowering annual species able to exploit soil moisture at depth in both deep sandy and gravelly soils in short (5 month) and medium (8 month) growing seasons. Ability to extract water from perched water table or from soil moisture at depth effectively extends its growing season. Very high herbage production. Very easy and cheap seed production for sale or further establishment on farm. Main shortcomings Susceptibility to viruses. Risk of bloat (though low). Links
Main reference Plants Database 2000; Hoveland C.S. and Evers G.W. (l995); Miller J.D. and Wells H.D. (l985) Other references Caradus J.R. (l995); Evers G.W. (l980); Evers G.W. (l999); Ocumpaugh W.R. et al. (l99l); Overman A.R. et al.(l992); Pedersen J.F. and Ball D.M. (l99l); Vidor M.A. and Jacques A.V.(l998); Wiley T.J. and Maughan C.M. (1993); Wiley T.J. et al.(1993) |