|Leguminosae||Author: Dr. John Frame|
Birdsfoot trefoil, birds-foot trefoil, upright trefoil, common
Glabrous to sparsely pubescent perennial plant, though not a long-lived perennial; life span from two to four years. Growth form ranges from prostrate to erect with numerous stems arising from a basal, well developed crown and branches arising from leaf axils. Primary growth comes from the crown but regrowth comes from buds formed at nodes on the stubble left after defoliation. Leaves are pentafoliate, alternately on short stalks with the two leaflets at the petiole base resembling stipules. The assymetrical pointed leaflets are mainly glabrous and are more slender and paler green than those of greater lotus.
Inflorescences with up to eight flowers, are umbel-like cymes at the end of long axillary branches. The calyx is a dentate tube and the yellow five-petalled corolla is often tinged red. The flowering period is indeterminate and so seed is set over an extended period in summer. The self-sterile plants are cross-pollinated, mainly by honey bees. Seed pods, 2-5 cm long, contain l5-20 seeds attached to the ventral suture; the seeds are released by a sudden split of the pod along both sutures after one to two weeks of ripening during which the pods change from green to brown. The seeds vary from round to oval in shape and from greenish yellow to dark brown in colour. The plant root system consists of a deep tap root with numerous secondary roots which have a good lateral spread. Some Moroccan genotypes produce rhizomes which arise from axillary buds on stem bases.
Natural distribution in western Europe and north Africa; secondary distribution in north-east and west-central USA, south-east Canada, southern Latin America. Also in eastern and central Europe, and parts of Asia. Circa l M ha grown in USA and 200 000 ha in Canada (Beuselinck and Grant, l995).
Perennial plant varying from prostrate to erect types, the former being more tolerant of poor drainage. Adapted to acid, infertile soils and also to saline soils. Has weak seedling emergence and a slow establishment phase. Moderate degree of drought resistance. Suited to low-input, extensive systems of animal production. Its range of adaptation is extending to warmer climes, e.g. south-east USA., because of the introduction of Mediterranean germ plasm into plant breeding (Hoveland et al., l990).
Season of growth.
Spring to autumn, but peak growth in mid summer.
Frost tolerance and regrowth.
Winter hardiness depends on cultivar provenance. North American and European cultivars are the most tolerant of low temperatures but are adversely affected by severe winters with fluctuating temperatures (Beuselinck and Grant, l995).
Optimum summer temperature for growth is circa 240C. At high summer temperatures susceptibility to fungal diseases increases.
Intolerant of shading from other plants, particularly during establishment. Is a long-day plant requiring daylengths of over l6 hours for full flowering.
Moderately drought resistant, but less so than lucerne (Peterson et al., l992).
Tolerance of flooding.
Tolerates poor soil drainage, and is more tolerant of flooding than lucerne, but not highly tolerant.
Because of its adaptation to infertile and acidic soils, it can be regarded as a pioneer forage legume. Has a moderate degree of tolerance to soil salinity . However, its agronomic performance responds to improve soil pH, drainage and fertility. Application of P and K on infertile soils enhances forage yield, seed yield and winter hardiness (Russelle et al., l99l)
Rhizobial inoculation of seed by effective, specific strains Rhizobium and Bradyrhizobium are needed when sowing, particularly on land where birdsfoot trefoil has not been cultivated before. Root nodules senesce after plant defoliation and a new generation develops during plant regrowth (Vance et al., l982).
Ability to spread naturally.
Mature seed from late-cut hay or seed crops can aid rejuvenation of stands. Intermittent flowering and seed set during the season from plants which have not been fully grazed down, as happens with less erect types, is another source of shed seed and grazed stands can be managed to allow a seed setting and shedding phase so as to maintain stand density.
Land preparation for establishment.
A well-cultivated, uniform, firm seed bed is required for best results since the small seeds require shallow sowing.
The seed is normally drilled or broadcast in spring after conventional seed-bed cultivations; broadcasting, surface oversowing and direct drilling (sod seeding) have been used on marginal land and roughland in north-east North America (Kunelius et al., l982) and in New Zealand (Lowther et al., l996).
Sowing time and rate.
Best sown in spring. If sown in autumn, sufficient time is needed for plants to develop before the onset of winter cold. Birdsfoot trefoil is sown at 6-l0 kg/ha for monocultures and at 3-5 kg/ha when sown with grasses, e.g. timothy (Phleum pratense), smooth-stalked meadow grass (Poa pratensis), red fescue (Festuca rubra). More competitive grasses, e.g. perennial ryegrass (Lolium perenne), cocksfoot (Dactylis glomerata) can also be used as companion grasses but such stands require management to favour regrowth and reseeding of the birdsfoot trefoil (Sheaffer et al., l984).
Number of seeds per kg.
715 000 to 835 000.
Percentage hard seeds.
Can reach 50% or more but germination capacity of hard seeds can be high (Hampton et al., l987).
Seed treatment before sowing.
Scarification or soaking the seeds in a gypsum solution reduces the percentage of hard seeds present.
Although adapted to low soil fertility, improvement of fertility by P and K application, and lime as required to raise soil pH, increase LAI, specific leaf mass and stem branching (Russelle et al., l985). Forage yield, seed yield and winter hardiness are enhanced on infertile, but not fertile soils, by P and K application (Russelle et al., l99l).
Compatibility with grasses and other legumes.
Compatible with non-aggressive grasses such as timothy, smooth-stalked meadow grass and brome grasses.
Ability to compete with weeds.
Because of its slow establishment ability, does not compete well then with broad-leaved weeds or aggressive volunteer grass weeds. Grass/birdsfoot trefoil associations are less prone to weed invasion generally than a birdsfoot trefoil monoculture.
Tolerance of herbicides.
Tolerates the so-called clover-safe herbicides e.g. MCPB, 2,4-DB, benazolin types, but not the less-selective herbicides.
Initially very poor and so clean seed beds are essential for a good establishment. Open swards are necessary when oversowing.
Vigour of growth and growth rhythm.
Once established, is capable of vigorous growth when well fertilized. Grows slowly during early spring and peaks in summer. Spring growth is directly proportional to the build-up of storage carbohydates in the roots (Alison & Hoveland, l989).
N-fixation of 60-l38 kg/ha is cited for North America (Heichel et al., l985; Farnham and George, l994). When grown in association with grass, most of the N in birdsfoot trefoil is derived from N2-fixation on account of the soil N being competitively taken up by the grass; the grass also benefits from transfer of fixed N from the legume (Farnham and George, l994).
Response to defoliation.
Regrowth depends on a sufficiency of axillary buds and photosynthesizing foliage being left after defoliation. This can be done by ensuring that adequate sites for regrowth remain after cutting crops for hay or silage, or by controlling the severity of defoliation when grazing. Prostrate cultivars are capable of more vigorous regrowth than erect types since more of their foliage escapes defoliation.
Some form of rotational grazing, and lax rather than severe, is the system most favourable to plant persistence and yield, particularly for erect-growing cultivars. This method also avoids the risk of birdsfoot trefoil being selectively overgrazed in mixed swards. A typical target stubble height is 5 to l0 cm since this leaves sites for regrowth on the stem stubble, but low-growing types can tolerate a lower stubble height because their procumbent growth habit ensures the presence of growth sites.
Birdsfoot trefoil is a tetraploid with a chromosome number of 2n=4x=24, though diploid types have been identified; outcrossing breeding system by insect pollen vectors.
Improvement in germination capacity of seeds at low temperatures, seedling vigour, yield, seed pod indehiscence and winter hardiness.
Dry matter yields.
Yields depending upon growing conditions. With l7 accessions on a free-draining calcareous soil in the UK, DM yields ranged from l0-l7 t/ha for birdsfoot trefoil/grass associations and from 6 to l4 t/ha for monocultures (Bullard and Crawford, l995). Such high yields would not be attainable on land of poor fertility soils.
Suitability for hay and silage.
Cultivars with an erect growth habit are the best suited for hay or silage cropping. Two or three cuts can usually be taken depending upon the length of the growing season. Yields are optimal at 6-week cutting intervals (Hoveland and Fales, l985). A companion grass improves stand density, reduces crop lodging and aids mechancal handling during hay making. The cutting height should be circa l0 cm so as to leave some foliage for photosynthesis and also allow axillary bud development from the stubble.
Value as standover or deferred feed.
Stockpiling in spring for summer utilization has been reported though forage quality declines with increasing time before use (Collins, l982).
Largely determined by stage of growth at time of utilization since feeding value falls with increasing maturity and associated stemminess. Although only one-third of the DM accumulates by the late vegetative stage, more than half the maximum amount of nutrients accumulates by then, and leaves generally have a higher mineral content than shoots, especially after the start of flowering (McGraw et al., 1986). The rate of decline of forage digestibility is greater in late than in early season (Buxton et al., l985). The overall forage quality under drought conditions is better than lucerne because of higher leaf:stem ratio, delayed maturity and improved quality of each plant fraction (Peterson et al., l992).
The presence of condensed tannins in the leaves and stems prevent bloating in ruminants and are nutritionally advantageous since they protect plant proteins in the rumen from degradation, thus allowing more protein to be utilized in the small intestine (Waghorn et al., l987). The types and combination of essential amino acids in birdsfoot trefoil are optimal for the production of high quality animal products (Waghorn et al., l990). The nutritional value of condensed tannins depends upon their concentration in the forage and levels of 20-40 g/kg DM are thought to be beneficial (Barry, l989).
Highly acceptable forage whether at vegetative stage for grazing or as conserved hay or silage.
Seed harvesting methods.
Seed production in North America is concentrated within latitudes 40-500N, e.g. in Canada and the upper mid-west of the USA., since long photoperiods and cool temperatures suit the physiological needs of the plant for seed production (Beuselinck, l997). Seed crops require careful timing and handling at harvesting to avoid high seed losses from pod dehiscence. Cutting and swathing the crop to dry slowly, or the use of chemical desiccation of the standing crop minimises pod shatter and loss of seeds.
Yields may reach 600 kg/ha but generally range from 50 to l75 kg/ha with a typical average of l00 kg/ha or less (McGraw et al., l986). The low seed yields achieved are the result of the indeterminate flowering habit, the limited supply of photosynthate to reproductive growth, flower and seed pod abortion, and pod dehiscence (McGraw and Beuselinck, l983).
Increased seed yield has been obtained from use of the growth regulator, paclobutrazol, to promote reproductive development and shorten the flowering period (Li and Hill, l989).
Seed quality standards.
Using the Fodder Plant Seeds Regulations of the United Kingdom as an example, certified seed require a minimum germination of 75% and a maximum permissible hard seed content of 40%, both percentages by number of pure seeds in the sample. The required analytical purity is 95% by weight for certified and commercial seed. The maximum total content of seeds of other plants permissible, also expressed as % by weight, is l.8% for certified seed and 2.8% for commercial seed.
There are two distinct types. European and Empire. The former has a faster seedling growth, thicker stems, a more upright growth, a more determinate flowering period and a faster regrowth after grazing (Grant and Marten, l985). The cultivars Empire, Dawn, Leo, Norcen and Carroll are among the most extensively used in North America (Beuselinck and Grant, l995). El Boyero, Quimey and San Gabriel are Latin American examples. Erect-growing cultivars are less persistent than low-growing cultivars under seven grazing pressure, one cause being that fewer leaves are left on the stubble to assist regrowt by their photsynthesis.
Crown and root rots, caused by a combination of Fusarium, Sclerotinia and Rhizoctonia spp. are the most significant diseases and are a factor in lack of plant persistence in south-east USA. (Beuselinck and Grant, l995).
Birdsfoot trefoil is susceptible to root-lesion nematode (Pratylenchus penetrans) and root-knot nematode (Meloidogyne spp.). A number of pests can adversely affect seed crops e.g. mirids (Lygus lineolaris), alfalfa plant bug (Adelphocoris lincolaris) but are controllable by standard pesticides (Wipfli et al., l990a,b). Seed chalcids (Bruchophagus platypterus) also reduce seed yield and are only controllable by early-season harvesting and burning plant debris after harvesting to reduce the population.
A pioneer, perennial legume adapted to wet, acid, infertile soil conditions. Drought resistant. Different cultivars available for mainly conservation and mainly grazing managements. Highly acceptable forage giving good animal performance. Does not cause bloat in cattle because of presence of condensed tannins.
Not a forage legume for high fertility soils where it is outperformed by other major forage legumes. Has a slow germination and weak seedling development. Seed production difficulties are a major limiting factor to its wider use.
Excellent individual animal performance reported for monocultures and birdsfoot trefoil/grass stands (Marten et al., l987). Performance is aided by the content of condensed tannins which improves the efficiency of protein metabolism; for example, in a comparison of birdsfoot trefoil and lucerne grazed by ewes and lambs, ewe wool production and lamb carcass weight were higher for birdsfoot trefoil (Douglas et al., l995).