Trifolium hybridum L.

Common name.

Alsike clover.
 

Description

Short-lived glabrous perennial which is a true species and not a hybrid as its name implies. Trifoliate leaves, leaflets being obovate with toothed margins and without the leaflet markings typical of red clover. Hairless stipules at the base of the peduncles taper to a point. Erect to decumbent growth habit with many slender, branched stems, 50-60 cm, emanating from a basal crown. The stems do not bear terminal flower heads and tend to lodge with age. Tap root with many lateral branches. Inflorescences axillary and borne on longer stalks than the leaves. Flowering is usually in mid summer, the globular racemes bearing 30-50 florets, 6-l0 mm, bracts absent. Calyx short and petals not fused into a tube as in red clover. Flowers pale pink to pinkish white becoming brown, shrivelled and deflexed after cross-pollination by honey bees. Two to four smooth, heart-shaped seeds, l mm long, in short, broad pods, green to greenish-brown, but darkening almost to black with age.

Distribution.

Mainly distributed in the cool temperate and sub-arctic zones of Europe, the Americas and Asia.

Characteristics.

Adapted to a wide range of environments but grows best in cool rather than warm temperate conditions. Tolerates infertile, wet, acid soils better than red clover but growth responds favourably to improved soil fertility; also reasonably tolerant of alkaline soils. Usually productive for 2-3 years. The forage is more succulent than that of red clover and so takes longer to cure when making hay.

Season of growth.

Has a vigorous flush of growth in summer but aftermath growth is poor.

Frost tolerance and regrowth.

Good degree of frost tolerance.

Drought tolerance.

Can tolerate considerable periods of drought.

Tolerance of flooding.

Moderately tolerant to periods of flooding.

Soil requirements.

Adapted to a wide range of soil texture types with low soil pH and low fertility but growth responds favourably to improved soil fertility. Tolerant of alkaline soils.

Rhizobium relationships.

Rhizobial N fixation in the nodules is by strains of Rhizobium leguminosarum bv. trifolii.

Ability to spread naturally.

Shed ripened seeds, whether from a late hay crop, a seed crop, or from irregular flowering/seed setting during the season, can sometimes aid rejuvenation of an ageing stand.

Land preparation for establishment.

A fine, firm tilth is required for the seed bed since a uniform, shallow depth of sowing is required for the small seed.

Sowing method.

The seed is normally drilled or broadcast after conventional seed-bed cultivations; aerial oversowing into low-fertility tussock grassland has been reported from New Zealand (Keoghan and Allen, l993).

Sowing depth and cover.

Shallow sowing at l0-l5 mm and a light but firm soil cover is advisable. However, for seed mixtures in which alsike clover is a minor constituent, the depth will be chosen to suit the major constituents which could be large-seeded grasses requiring deeper sowing.

Sowing time and rate.

Generally sown in spring or late summer when there is sufficient soil moisture for seed germination. For hay production in western North America typically sown at 4-8 kg/ha in mixture with timothy (Phleum pratense). In New Zealand, 2 kg/ha has been used as part of a mixed legume mixture for oversowing indigenous tussock grassland. Low seed rates (2.2-4.5 kg/ha) and narrow (l5 cm) row spacing proved better for seed production than higher seed rates and wider spacings (Townsend, l985).

Number of seeds per kg.

Circa l 500 000.

Percentage hard seed.

Variable but usually fairly low at 5-l0%.

Nutrient requirements.

Establishment benefits from a supply of readily-available, water-soluble P. Replenishment of P and especially, K is required following removal of hay or seed crops. Although adapted to low fertility, alsike clover growth responds favourably to improved soil pH and fertility.

Compatibility with grasses and other legumes.

Compatible with non-aggressive grass species such as timothy but not with aggressive grass species such as perennial ryegrass (Lolium perenne). Compatible with white and red clovers except on highly fertile soils when red clover will become dominant.

Ability to compete with weeds.

Relatively low in the early establishment phase when sown in monoculture.

Tolerance of herbicides.

Tolerates so-called ‘clover-safe’ herbicides, e.g. MCPB, 2,4-DB, benazolin types, but not the less-selective herbicides.

Seedling vigour.

Initially poor on account of small seed size.

Vigour of growth and growth rhythm.

Vigorous in monoculture or in mixtures with non-aggressive companion grasses but relatively poor as a minor constituent of multi-species, general-purpose seed mixtures, except in the first harvest year. There is a major growth flush in early summer but aftermath growth is poor following a hay or seed crop. Growth is curtailed by low temperatures in late autumn.

Response to defoliation.

Best suited to an infrequent defoliation regime such as cutting for hay or silage.

Grazing management.

A rotational grazing system is best for plant persistence and production.

Breeding system.

Alsike clover is a self-incompatible species, cross-pollinated by honey bees. It is a natural diploid with a chromosome number of 2n=2x=l6. Tetraploid forms, with 2n=4x=32 chromosomes, have mainly been developed in Europe and are as fertile as the original diploids.

Breeding objectives.

Improved yield and persistence.

Dry matter yields.

Forage yields normally decline with age of stand. In northern Sweden, yields from timothy/alsike clover mixtures were lower than from timothy/red clover on a range of soil texture types with pH levels of 4.9 to 6.4, though differences were smaller at the lowest pH (Wallgren et al., l995); DM yields from the alsike clover stands declined from 5.6 t/ha in the first harvest year to 4.5-5.5 t/ha in the third. Higher yields than these have been reported from irrigated stands in Colorado State, western USA (Townsend, l985).

Suitability for hay and silage.

Growth characteristics and the favourable growth response to infrequent defoliation make it a suitable species for conservation. Valued for hay production at irrigated, high-altitude sites in western USA (Pederson, l995).

Value as standover or deferred feed.

Not a common method of utilization but stockpiling of summer growth for use in autumn and winter has been reported from the high country in New Zealand (Widdup and Ryan, l994).

Feeding value.

Generally regarded as having a similar feeding value to red clover at equivalent stages of growth. Has a high protein content.

Acceptability.

Highly acceptable forage to livestock either as hay or when grazed at a young, leafy growth stage.

Anti-quality factors.

Bloat can occur in cattle when grazing alsike-rich stands but conventional prevention methods as used for red clover stands can be implemented.

Seed harvesting methods.
 

Most of the world’s seed supply is produced in Alberta Province, south-western Canada. Irrigation is applied in summer as necessary to prevent moisture stress at flowering which could reduce seed yield.

Seed yield.

Very variable. Average between l00 and 200 kg/ha though much higher yields have been obtained under optimal growing and harvesting conditions.

Seed quality standards.

Using the Fodder Plant Seed Regulations for the United Kingdom as an example, certified and commercial seed require a minimum germination of 80% and a maximum hard seed content of 20% by number of pure seeds. The required minimum analytical purity is 97% by weight. The maximum permissible content of seeds of other species is l.5% by weight for certified seed and 2.5% for commercial seed.

Cultivars.

A small number of improved cultivars have been released over the years, e.g. diploids Aurora and Dawn (Canada), tetraploids Frida and Tetra (Sweden) diploid Ermo Øtofte (Denmark).

Diseases.

Susceptible to many of the diseases which affect red clover such as powdery mildew (Erysiphe trifolii), rusts (Uromyces spp.) and sooty blotch (Cymadothea trifolii), but less susceptible to Sclerotinia root and crown rot (Sclerotinia trifoliorum) and resistant to clover scorch syn. northern anthracnose (Kabatiella caulivora) and southern anthracnose (Colletotrichum trifolii).

Viruses.

Virus presence, e.g. alfalfa mosaic, can cause a range of effects on plant vigour from negligible to severe.

Pests.

Regarded as susceptible to the same range of pests as red clover.

Main attributes.

An option in place of red clover for cold, infertile, acidic soils. Suitable species in mixture with a non-competitive grass such as timothy for hay production.

Main shortcomings.

Although a perennial, alsike clover is relatively short-lived, and productive for only 2-3 years. Yield declines with age. Lower yielding than red clover on fertile soils. Can cause bloat in cattle.

Links for the genus:

• The true clovers: Exploration, preservation, evaluation and enhancement
• Clovers: Cultural specification and management of several species
• Insect pollination of clover species: Chapter 3 of the Virtual Beekeeping Book
• Sorting Trifolium names: Database of synonymes and common names
• Cover crops: Rich information with links to species, references and photographs

Main references.

Frame et al. (l998); Pederson (l995); Townsend (l985).