Trifolium alpinum (Schröter, 1888)
Perennial, with a taproot that can be more than 1 m long and very robust, 0.5-1 cm thick, fading to a thick, short rootstock, branched and covered with the remains of brown leaf sheaths.
Above ground, stems are compressed, very short, ascending, with tight leaf sheaths because of the stipules of the distichous foliage leaves, appearing to form rosettes that are aggregated to dense turfs.
Entire plant glabrous. Foliage leaves always ternate, petioles 2-7 cm long; leaflets lanceolate to lineal, rarely broadly elliptic, 1-5 cm long and 3-7 mm wide, acute, freshly green (yellow in autumn), smooth, with a faint main vein and many lateral veins that are capillary, acute-angled, furcated up to three times and connected reticulately, almost entire; margin teeth a little thickened, scarcely prominent.
Stipules up to 4 cm (exceptionally up to 9 cm) long, covering above ground stems entirely, highly connate with the petioles, membranous.
Flowers 18-21 mm long, slender, redolent and fragrant, at the beginning erect to horizontal, drooping after flowering. Corolla pink-incarnadine to light crimson, coated purple, scarcely yellowish-white, at the end light brown, scarious.
SUITABILITY FOR RESTORATION
This central and south European species occurs in the Alps, in the subalpine and alpine zone. It prefers soils that are limedeficient, comparatively nutrient-deficient, deep, warm and not too wet. On lime-rich soils it only grows on a thick humus layer. It is typically found in Narduus pastures and poor alpine grasslands.
In the Alps, it is common between 1 700 and 2 500 m, sometimes below the timber line. Because of its suitability for sites with a low pH as well as its deep taproot, alpine clover is an important component (and nitrogen supplier) of grassland mixtures that are appropriate to the habitat. Nutrient-rich forage with high digestibility.
Seeds ovoid to round, 2.5 mm long, 2 mm wide and 1.5 mm thick, radicle sticking out conspicuously.
Testa thick, slightly glossy or dull, tawny or greenish-brown to brown.
Pods brown, ovoid, one-to two-seeded.
Seeds germinate badly without scarification; up to 85 percent of the seeds have a firm testa.
Thousand seed weight: 4.8-5.2 g.
(soil and climate)
Alpine clover has special requirements regarding the suitability of a site for reproduction.
There should be no pathogenic nematodes of the gender Pratylenchus in the soil; otherwise total losses in seed multiplication will occur.
The pH must be low, with an optimum range between 4.5 and 5.4. There should be sufficient phosphorus in the soil for rapid juvenile development.
Inoculation with soil from the site stimulates the growth rate, as demonstrated in experiments.
Scarification (e.g. mechanical carving of the testa with sandpaper) is necessary for a good, rapid germination.
Alpine clover requires a fine, crumbly seedbed with compact topsoil.
Seed depth: 1.5-2.0 cm.
Open sowing is possible by means of strip or row seeding. In order to guarantee a satisfactory crop yield the following year, seeds should be sown up to the end of May at the latest.
There is as yet no experience with cover crops.
Seed rate: 14-18 kg is necessary at least, in order to obtain satisfactory population density.
Row spacing: 12-25 cm. Depending on the construction of the seeder and the method of weed control there should be either dense populations or sufficient row spacing (for mechanical and/or chemical weed control).
Phosphorus and potassium: alpine clover does not require many nutrients.
In autumn before cultivation, basic fertilization with manure (15-20 tonnes/ha) is considered sufficient. Using mineral fertilizer, an application of 40-60 kg/ha P2O5 and 80-100 kg/ha K2O is recommended, depending on soil content.
Nitrogen: alpine clover meets its nitrogen requirements by means of nitrogen-fixing bacteria. As for all legumes, fertilization with 20-30 kg/N is recommended for open sowing in order to stimulate juvenile development.
MAINTENANCE AND WEED CONTROL
This species has a slow juvenile development and produces conspicuously little leaf mass. Thus, populations with acceptable weed infestation are only possible if there is mechanical weed control (weeding, brushing and hoeing between rows) optimally combined with chemical control.
As for all legumes, specific chemical weed control of grasses is possible. To date there has been no recorded experience of the specific chemical control of dicotyledonous plants.
HARVEST AND YIELDS
Resistance to lodging: high.
Shattering tendency: low.
Ripeness: at time of ripeness the pods change colour to brown. The seeds become firm (nail test) and change colour to a typical tawny or greenish-brown to brown. The ripeness of the population is quite compact.
Ripening period: at the end of June up to the beginning of July.
Harvesting technique: there has been little experience to date. However, the harvester board should be kept very low and threshing carried out with great care.
Crop yields: in the first experimental cultivation only a few plants flowered in the first harvesting year. Cultivation already carried out - where there were organic farming conditions - produced only low crop yields of a few kilograms per hectare. Future experiments will provide further information about potential yields.