- Economic importance
- History of the crop
- Cultivation areas
- Botanical description
- Biological features
- Plant nutrition
- Crop rotation
- Crop care
- Growing for seeds
- Growing for green manure
The green mass of sweet clover is used for livestock feed, for making hay, haylage and silage. By the time of flowering, the protein content in the dry mass reaches 19%. For fodder purposes, single-species crops or grass mixtures are used.
100 kg of sweet clover hay harvested in the flowering phase contains 44.0-44.5 feed units and 11.1-11.9 kg of digestible protein. 100 kg of fresh grass – 18.2-19.5 feed units and 3.1-3.2 kg of protein.
It is also suitable for grazing from early spring to late autumn in the first – second years of life, 3-4 grazing per year. With sufficient moisture, it grows back in 18-20 days. In the first 3-4 days of grazing, animals eat it badly because of the bitter taste and pungent odor due to the content in plants up to 1.5% coumarin. However, later the animals get used to it and willingly eat it, especially before the onset of budding. In plants of yellow sweet clover, the content of coumarin is higher than in white. Also, in the conditions of the arid steppe zone, its content is higher than in the humid forest-steppe zone. The peak content of coumarin in plants falls on the period of full flowering – the beginning of maturation. During the day, the peak occurs at noon, so grazing and mowing for fodder is preferably carried out in the early morning or evening. There are non-coumarin forms of sweet clover. According to studies, the harmful effects of coumarin on animal health have not been established. Feeding sweet clover helps to improve digestion in animals; in some cases, milk can acquire a specific smell.
Just like alfalfa and clover, sweet clover often causes the development of timpania in animals, so cattle are released to graze this crop after natural meadows or cereal grasses so that animals do not eat a large amount of fresh grass at one time.
In terms of chemical composition, sweet clover is similar to alfalfa, clover, sainfoin, but somewhat worse in terms of nutritional value and palatability.
For the preparation of silage, grass mixtures of sweet clover with cereal herbs are better suited.
Sweet clover is distinguished by high drought resistance, frost resistance and salt tolerance, as a result of which it is considered one of the best phytomeliorants. Its cultivation contributes to the desalinization of the soil, its enrichment with nitrogen, making the soil suitable for the cultivation of more demanding crops, such as spring wheat , millet, sugar beet, etc. Suitable for restoring the fertility of solonetzes, sand, mine dumps, quarries, ravines and eroded slopes with completely or partially removed fertile soil layer, and unsuitable for other plant species.
Sweet clover is one of the best crops used for green manure due to high yields of green mass. When it is plowed into the soil with green mass, 150-200 kg/ha of nitrogen is introduced, which approximately corresponds to the application of 30-40 t/ha of manure.
Honey plant. In terms of the quantity and quality of the collected honey, sweet clover surpasses phacelia and other honey crops, the collection from 1 ha reaches 600 kg.
The disadvantages of the culture include: the content of coumarin in the aerial parts of plants, the coarsening of the stems after flowering, the shedding of seeds and leaves during hay drying, and the clogging of fields with carrion.
History of the crop
Sweet clover was first introduced into culture as green manure in the eastern Mediterranean more than 2 thousand years ago.
In Western Europe and in the USA, it has been grown since the 18th century.
In Russia, sweet clover was known as a medicinal and honey plant.
Currently sweet clover is grown in North America and Europe as a green manure and honey crop. In Russia, it is cultivated in the arid regions of Western Siberia, the Volga region, and the Central Black Earth zone.
The yield of sweet clover hay on light chestnut soils is 2-3 t/ha, on elevated floodplains and chernozems is 4-6 t/ha. The yield of green mass is 18-20 t/ha, seeds – 400-800 kg/ha.
Under irrigation conditions, the yield of green mass is 39.6-42.7 t/ha (Omskoye farm, Siberian Research Institute of Forages).
There are 20 species; white sweet clover and yellow sweet clover are used in agriculture.
Fragrant sweet clover (M. suaveolens Ledeb.), toothed sweet clover (M. dentatus Pers.), Volga sweet clover (M. wolgicus Poiz.) and Polish sweet clover, or Caspian sweet clover (M. polonicus (L.) Pall) are also considered promising species of sweet clover.
White sweet clover
White sweet clover (Melilotus albus Medik.) is a biennial plant.
The root is taproot, lateral roots are well developed, it penetrates into the depth of the soil up to 1.5 m in the first year of life and up to 2-3 m in the second.
The stem is straight, rarely ascending, 75-300 cm high, hollow. Branching of the stem begins at a height of 25-30 cm. In the upper part, the stem is shortly pubescent, at the bottom it is bare.
The leaves are trifoliate, the leaflets of the lower and middle tiers are rounded, the upper ones are linear or narrowly elliptical, serrated at the edges.
Inflorescence – axillary raceme. The flowers are white. Cross-pollination and self-pollination.
The fruit is a single- or rarely two-seeded bean, elliptical in shape, reticulate-wrinkled with a short, sharp nose. Seeds are oval, yellow or yellowish green. Weight of 1000 seeds 1.5-2.4 g.
It is cultivated throughout the European part of Russia: from the Caucasus and the Crimea to Arkhangelsk and Murmansk, as well as in Siberia and Central Asia.
Sweet clover yellow
Yellow sweet clover (Melilotus officinalis Pall.) is a biennial plant, rarely an annual.
The root is taproot.
The stem is strongly branched, erect or ascending, with anthocyanin coloration.
The leaflets of the lower tier are obovate or rounded, the upper ones are oblong-lanceolate. Leafiness is less than that of white sweet clover.
The inflorescence is a long brush. The flowers are yellow.
The fruit is an ovoid bobo, transversely wrinkled. Seeds are yellow, yellow-green. Weight of 1000 seeds 1.5 g.
It is cultivated mainly in the southern steppe regions of the country, although the area almost coincides with the area of the white sweet clover.
Sweet clover belongs to winter-hardy plants, in this property it is equivalent to alfalfa. Winter hardiness depends on the location of the root neck in the soil, while the deeper it lies, the higher the winter hardiness of plants.
The higher the winter hardiness of a particular sweet clover variety, the higher its drought resistance. Therefore, varieties of steppe origin are more winter-hardy than varieties or forms of more northern origin.
Ecological is very plastic, withstands high temperatures in summer and low in winter, including spring frosts down to -3 … -5 °C.
Seeds germinate at a temperature of 3-4 °C, optimally 7-8 °C.
Sweet clover is a drought-resistant plant. The critical period in relation to drought falls on the flowering phase. With a lack of moisture during this period, it leads to the dropping of leaves and the deterioration of the fodder quality of hay. The yellow sweet clover is more drought-resistant than the white sweet clover.
Sweet clover is a photophilous plant.
It is not demanding on soils, but prefers loose loamy and chernozem, lime-rich soils with a neutral or slightly alkaline reaction. In the Non-Chernozem zone, it gives good yields on production fields with a pH of the soil solution of at least 5.6. It can grow on light sandy, solonetsous, moist solonchak, heavy clayey, heavily limed, stony and structureless soils.
Poorly tolerates acidic, swampy, highly moist, highly podzolized soils and loose sands.
White sweet clover can endure flooding for up to 12 days.
The removal of nutrients from the soil by sweet clover is higher than that of grain crops : in terms of calcium removal, it exceeds them by 3-5 times, potassium – by 2-3 times, phosphorus – by 1.5-2.5 times.
For the formation of 1 ton of hay, 3-3.5 kg P2O5, 20-24 kg K2O, 15-16 kg CaO are removed from the soil.
White and yellow sweet clover are plants of the spring type of development, represented mainly by biennial forms.
A two-year-old sweet clover, when sown under the cover of another crop, forms a rosette in the first year of life and does not bloom. However, if the cover crop is harvested early and the stand is well maintained, a small cut can be achieved by the end of the growing season. With coverless sowing and sufficient moisture, sweet clover grows up to 45-75 cm, in some years it can even give two mowings in the first year of life.
In the second year of life, sweet clover starts growing earlier than winter rye, awnless brome or alfalfa. Already in early May, the height of plants can reach 25-30 cm.
In the second year of life, white sweet clover grows up to 150-350 cm, yellow – up to 100-150 cm. The first cut is usually used for hay, haylage or silage, and aftermath – for green fodder. With an early first mowing, it is possible to get seeds from the second mowing. With sufficient moisture, sweet clover can produce 2-3 cuts, provided that the first mowing is early (no later than budding) and cut at least 12-15 cm to preserve the renewal buds, which are located relatively high on the stem.
When receiving seeds from plants of the second year of life after the first mowing, sweet clover quickly reaches the fruiting phase, but its fodder quality decreases.
In the spring, regrowth begins from the renewal buds located on the root collar. Regrowth after mowing occurs from the buds located in the axils of the stem. Therefore, the more axillary buds remain in the uncut part of the stem, the faster regrowth occurs after mowing.
The maximum increase in the above-ground mass falls on the period from the beginning of regrowth to flowering. In the budding phase, it averages 3-5 cm per day.
In early northern forms, the duration of the flowering phase is 14-28 days, in late southern forms – 30-45 days. Flowering of an individual brush lasts 8-14 days, while the flowers of the lower part of the brush bloom first. After flowering, the stems quickly coarsen.
When ripe, the beans crumble easily, which is taken into account when determining the optimal harvesting time.
The vegetation period of sweet clover is 80-140 days. According to the duration of the growing season, it is divided into:
- early (80-95 days);
- mid-late (95-110 days);
- late (110-125 days);
- very late (125-140 days).
The earliest forms are cultivated in the forest zone of Russia (Arkhangelsk, Vologda, Leningrad regions); middle-late – forest-steppe and steppe; later – in dry steppes; very late – in the countries of the Mediterranean Sea. The longer the growing season, the taller the plants grow. Early forms of yellow sweet clover are found in the Caucasus (vegetation period 85-90 days), late-ripening ones – in the valleys of Azerbaijan (vegetation period 130-140 days).
The height of plants of late forms reaches 3.5 m, early – 1.5 m, sometimes 2 m.
The best predecessors of sweet clover in crop rotation are row crops, for example, potatoes, beets, corn. However, it is an unpretentious crop, so it can be grown after any crop.
The introduction of phosphorus fertilizers under the sweet clover in the northwestern regions of Russia increases the yield by 1.5-2 times (Leningrad Agricultural Institute). Also, this culture is distinguished by the ability of the root system to absorb sparingly soluble phosphorus compounds, so phosphate rock shows high efficiency, especially on acidic soils.
In the conditions of the Omsk region, the introduction of phosphate and potash fertilizers increased the yield of hay from 4.1 to 4.9 t/ha.
Recommended fertilizer application rates: 300-400 kg/ha of superphosphate, 150-200 kg/ha of potassium salt. Fertilizers are applied under the cover cult or after its harvesting at the end of summer.
In the conditions of the Non-Chernozem zone, liming soils to full hydrolytic acidity (1.5-2 t/ha) sharply increased the yield.
Usually sweet clover is sown under cover, so the tillage corresponds to that of a cover crop.
With coverless crops, processing is carried out in the same way as for small-seeded perennial grasses.
One-year sowing of sweet clover mixed with Sudanese grass or corn for silage is also practiced.
In the conditions of arid steppe, it is recommended to grow sweet clover without a cover in order to obtain green mass in the year of sowing. In more humid conditions of the forest-steppe, it is sown under the cover of spring cereals, millet, mogar or fodder crops.
Sweet clover is distinguished by a large number of hard seeds (70-80%), which, while remaining viable for up to 10 years, may not germinate in the year of sowing, which causes clogging of subsequent crops. This feature is due to a very dense seed coat, which does not allow water to pass to the embryo. Therefore, for its violation, a special method of preparing seeds is used – scarification, or scratching, with the help of scarifiers or passing the seeds 1-2 times through a clover grater.
Before sowing, the seeds are cleaned and treated with bacterial preparations on the day of sowing, for example, nitragin.
The seeding rate of sweet clover seeds for fodder and green manure is 15-20 kg/ha in the steppe zone, 20-25 kg/ha in the Non-Chernozem zone, and 7-8 kg/ha for seeds. On eroded soils, for the formation of a long herbage, the seeding rate is increased to 25-30 kg/ha.
Sowing depth – up to 3 cm.
Sowing time – simultaneously with the sowing of spring cereals, or, less often, after the formation of 2-4 leaves in the cover crop.
The method of sowing for fodder and green manure is the usual ordinary with the help of disc seeders, for seeds – wide-row (7-8 kg/ha).
If sowing is carried out under annual grasses, then it is recommended to harvest them for green fodder, and not for hay, in order to free the field earlier. If the cover crop is barley, then harvesting is best done on a high cut with combines with choppers, immediately removing straw from the field.
When ripe, the cover crop is immediately removed. The earlier it is removed, the more renewal buds will form on the root collar of the sweet clover and the better the plants will develop in the fall and the higher the yield of hay or seeds in the second year of life.
If necessary, mineral fertilizers are applied after the cover crop has been harvested.
Harvesting of sweet clover for hay is started in the budding phase – the beginning of flowering. Harvesting late results in coarse hay with a high coumarin content. The cutting height is 12-18 cm, with such a cutting height, better and faster drying of the green mass is achieved, losses during harvesting are reduced and good sweet clover regrowth is ensured.
When making hay, there are often large losses due to leaf fall. Therefore, for the final drying of the dried mass, it is recommended to use installations with active ventilation.
Growing for seeds
Sweet clover has a high seed productivity. One plant can produce up to 17 thousand seeds, from one hectare – up to 1.5-1.7 t/ha. This is due to the possibility of cross-pollination and self-pollination, as well as pollination of flowers not only by bees, wasps, bumblebees, but also by other insects. Even in unfavorable years with cold and damp summers, it can produce up to 700-800 kg/ha of seeds. Therefore, large areas of seed plots are not required for industrial crops. One hectare seed plot can provide seeds for 100 hectares. Seeds can be obtained from ordinary crops or special seed plants, in which sweet clover is planted in a wide-row way with row spacings of 45-60 cm.
Seeds can be obtained from ordinary herbage from the first or second mowing. Mowing of seed plants begins when 1/3 of the beans turn yellow, but no later than 2/3 of the beans turn brown. Beans ripen well in windrows. The dried mass is harvested by combines with a grater and threshed. Seeds are cleaned, dried to a moisture content of not more than 15% and stored for long-term storage.
In Western Siberia, when irrigated, summer crops of sweet clover are not inferior to early spring crops in terms of productivity. Thus, the seed yield when sown in May amounted to 1.05 t/ha, in June – 1.11 t/ha, in July – 1.12 t/ha.
Growing for green manure
Sweet clover is recommended to be grown for green manure in seeded fallows in the northern regions, where lupine and seradella do not have time to produce mature seeds. This crop grows well on saline soils of the steppe zone.
For green manure, crops of the first or second year of life can be used with plant heights of 30-35 cm or more. It is usually grown in busy or green manure pairs, incorporation into the soil is carried out in the second year of life.
Agricultural technology is common. The timing of plowing depends on the conditions of cultivation. In the northern regions, plowing is carried out in June-July, in areas with a long summer period, the green mass of the second cut is plowed, while the first cut is used for hay or haylage.
Before plowing, the green mass is rolled and crushed with disc harrows or cultivators. Sometimes, for this, a small wooden roller is installed behind the tractor in front of the first plow body, crushing the grass before plowing. The plowing depth is 13-15 cm on heavy soils and 16-18 cm on medium and light soils.
On saline lands, non-moldboard processing, milling or plowing with three-tier plows is used. Salt soils are usually little weed infested, therefore, in these conditions, coverless sowing is carried out in early spring. Seeding rates with a continuous sowing method are 20-25 kg/ha, with an interrow sowing – 10-12 kg/ha.
The yield of spring wheat sown after sweet clover was 2.1 t/ha (Leninsky state farm, Kokchetav region, Kazakhstan). The yield of wheat in the Irkutsk region after sweet clover increased by 0.4 t/ha, barley – by 0.4-0.6 t/ha. The yield of rye grain in Estonian conditions after sweet clover fallow was 2.9 t/ha on average over 5 years, which is higher than in black fallow fertilized with manure.
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