Snow clover
Trifolium pratense ssp. nivale (Hegi et al., 1977)
BOTANY
Alpine subspecies of Trifolium pratense. Perennial, with a robust taproot up to 60 cm long, strong lateral roots and a short rootstock without rhizomes. Main axis compressed, procumbent or transversally ascending; basal leaf rosette.
Stems come off the axis of the lowest rosette leaves, mostly with three to five internodes, simple or with short branches, erect, ascending only basally, 20-50 cm high, often slightly compressed, grooved to angular, often coated red, with dense hairs. Hairs of entire plant are whitish.
Basal foliage leaves with long petioles (15-20 cm), upper leaves with shorter ones or almost sessile.
Leaflets very short, petiolate, mostly 1.5-3 cm long, obovate to broadly elliptic, mutually rounded or marginally blunt with a point or slightly emarginate, hairs appressed and soft. Adaxially (upper leaf surface) freshly green, often with light green or auburn spots or cross bands, abaxially (lower leaf surface) glaucous. Stipules ovate-lanceolate, highly connate with the petiole; with triangular, sharp apices, membranous; veins are green or red, connected reticulately, outwardly pilose.
Flowering heads white, pink or magenta, one to four per stem; the upper ones appear to be terminal, often close together in pairs, spherical to ovate, mostly covered by the stipules of reduced foliage leaves, rarely having longer petioles, 2 cm wide; with 30 to 60 flowers that are non-petiolate, 1.3-1.8 cm long and always erect.
SUITABILITY FOR RESTORATION
This plant of the central and southern European mountains occurs in the subalpine and alpine zone. It grows on rich meadows and pastures, in low-density stands and fields and also on poor alpine grasslands. Common and frequent, mainly on sunny slopes, on loam which is moist, not lime-deficient, slightly acid to neutral and sandy, or on raw soils with loam.
Suitable for restoration in the subalpine and alpine zones, on soils with a low humus content; deep root system (therefore a good protection against erosion) accumulating nitrogen, good tolerance of PK fertilization, valuable forage plant.
Seeds
SEEDS
Seeds 1-2.3 mm long, 0.8-1.5 mm wide and 0.5-1 mm thick; inclined kidneyshaped (scarcely ovoid) to obtusely triangular in contour. Radicle half as long as the cotyledons, often distinctly contrasted by a groove on either side.
Hilum small, round, lying within the indentation.
Surface with different colours, mostly yellow or purple, smooth, glossy.
Pod one-seeded, ovoid, 2.5 mm long and 1.8 mm wide, always with a cap.
Thousand seed weight: 1.2-1.6 g.
REQUIREMENTS
(soil and climate)
Like Trifolium pratense, snow clover is not self-tolerant. In order to avoid socalled „clover tiredness“ (accumulation of nematodes and/or fungus pathogens) the plant should only be cultivated on the same field every six years.
Soils are preferred that are intermediate to medium heavy, deep, rich in humus, not too acid, and easily warmed.
Arable land that tends to drought should be avoided.
CULTIVATION
In order to minimize crossbreeding between snow clover and Trifolium pratense, a distance of at least 300 m between production fields and meadows should be maintained.
Snow clover needs a clean, fine, crumbly seedbed with compact soil.
Normally the plant is cultivated below a cover crop in spring. Sowing is carried out by means of a seeder and the seed depth is 0.5 cm.
Single plant
Open sowing after the corn harvest in summer is also possible. In order to guarantee sufficient plant development until autumn, sowing should be carried out up to the third week of August. Delays in germination caused by summer drought can be avoided by irrigation.
Seed rate: 8-12 kg/ha. By open sowing in summer, an increase of the seed rate up to 15 kg/ha can be obtained.
Row spacing: 15-20 cm.
FERTILIZATION
Phosphorus and potassium: nutrient requirements are intermediate. Before cultivation, basic fertilization with manure (20-25 tonnes/ha) is considered suffient. Using mineral fertilizer, an application of 60-80 kg/ha P2O5 and 100-160 kg/ha K2O is recommended, depending on soil content.
Nitrogen: snow clover meets its nitrogen requirements by means of nitrogen-fixing bacteria. Preceding crop effect is about 60-80 kg N/ha.
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
A general problem in cultivating snow clover is the risk of crossbreeding with the lowland Trifolium pratense.
When this occurs, the second or third generation cultivated in lowland regions changes the habitus. Plants grow taller and can partly be treated like ordinary Trifolium pratense However, their particular suitability for restoration in high altitudes remains.
If growth conditions are optimal, one or two cleaning cuts in the seeding year have to be carried out. If necessary, weed control with herbicides should be carried out in the seeding year. Snow clover is not sensitive to the use of curry combs.
As snow clover is a long day plant, the first growth in the harvesting year is not used for seed cultivation. Depending on climate, the population (approximately 10 cm high) is cut in late April or the first decade of May. The following second growth is threshed, ensuring an optimal content of seedlings.
If the population is dense and has no weed species after the first year, optimal maintenance will allow a second harvesting year.
Flowering plants
HARVEST AND YIELDS
Resistance to lodging: intermediate.
Shattering tendency: low, whereas continuous rainfall after ripeness increases the risk of outgrowth.
Ripeness: the beginning of ripeness is indicated by darkening of the population. The ripe flowering heads change colour to dark brown. If a flowering head rubbed between the hands releases firm clover seeds, the population can be threshed when 80 percent of the population reaches this stage.
Ripening period: from the last decade of July until the middle of August, depending on climate and cut of the first growth.
Harvesting technique: if weather conditions are sunny and dry, snow clover can be threshed directly. Swath threshing is not recommended. With unfavourable weather conditions at harvesting time, a socalled ripening spraying with Diquat (3-4 l/ha) can be carried out. Only the assimilating leaf area is killed by this contact herbicide and the plant will recover and grow again. The population dries quickly and can be harvested after one to three days; because of this, interference with germination is possible. In order to rub the clover seeds off the flowers successfully, the population should be as dry as possible.
Crop yields: yields are far below those of commercially cultivated Trifolium pratense. On an average, 150-200 kg/ha can be produced, whereas a yield increase can be expected only after several years of practical experience.
