Legume
A legume is a plant in the family Fabaceae, or the fruit or seed of such a plant. When used as dry grain, the seed is called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock forage and silage, and as soil-enhancing green manure. Well-known legumes include alfalfa, clover, beans, peas, chickpeas, lentils, lupins, mesquite, carob, soybeans, peanuts, and tamarind. Legumes produce a botanically unique type of fruit – a simple dry fruit that develops from a simple carpel and usually dehisces on two sides.
Legumes are notable in that most of them have symbiotic nitrogen-fixing bacteria in structures called root nodules. For that reason, they play a key role in crop rotation.
Terminology
The term pulse, as used by the United Nations' Food and Agriculture Organization, is reserved for legume crops harvested solely for the dry seed. This excludes green beans and green peas, which are considered vegetable crops. Also excluded are seeds that are mainly grown for oil extraction, and seeds which are used exclusively for sowing forage. However, in common usage, these distinctions are not always clearly made, and many of the varieties used for dried pulses are also used for green vegetables, with their beans in pods while young.Some Fabaceae, such as Scotch broom and other Genisteae, are leguminous but are usually not called legumes by farmers, who tend to restrict that term to food crops.
History
Archaeologists have discovered traces of pulse production around Ravi River, the seat of the Indus Valley Civilisation, dating to c. 3300 BCE. Meanwhile, evidence of lentil cultivation has also been found in Egyptian pyramids and cuneiform recipes. Dry pea seeds have been discovered in a Swiss village that are believed to date back to the Stone Age. Archaeological evidence suggests that these peas must have been grown in the eastern Mediterranean and Mesopotamian regions at least 5,000 years ago and in Britain as early as the 11th century. But one particular bean has become the leading legume planted worldwide, the soybean. It was first domesticated around 11000 BC in China, a descendant of the wild vine Glycine soja.In the United States, domesticated soybean was introduced in 1804 from France by Benjamin Franklin in Philadelphia. Henry Ford, a vegetarian, was the first person to use soybeans for large-scale industrial purposes. Concentrating on his company, from 1932 to 1933 he invested over 1 million dollars in research on soybeans. Prior to World War II, 40% of cooking oil was imported into the US. When the war came, supply routes were disrupted, which encouraged the soybean culture in the US. Due to the years of research done by Henry Ford, the domestic soybean oil industry was born. Between 1970 and 1976, soybean production increased approximately 30%. Oil yield from bulk soybeans averages about 18%. Its modern-day usage ranges from margarine, salad oils, shortening and the previously mentioned cooking oil.
Uses
Farmed legumes can belong to many agricultural classes, including forage, grain, blooms, pharmaceutical/industrial, fallow/green manure, and timber species. Most commercially farmed species fill two or more roles simultaneously, depending upon their degree of maturity when harvested.Human consumption
Grain legumes are cultivated for their seeds, which are used for human and animal consumption or for the production of oils for industrial uses. Grain legumes include beans, lentils, lupins, peas, and peanuts.Nutritional value
Legumes are a significant source of protein, dietary fiber, carbohydrates and dietary minerals; for example, a 100 gram serving of cooked chickpeas contains 18 percent of the Daily Value for protein, 30 percent DV for dietary fiber, 43 percent DV for folate and 52 percent DV for manganese.Legumes are also an excellent source of resistant starch which is broken down by bacteria in the large intestine to produce short-chain fatty acids used by intestinal cells for food energy.
Preliminary studies in humans include the potential for regular consumption of legumes in a plant-based diet to reduce the prevalence or risk of developing metabolic syndrome. There is evidence that a portion of pulses in a diet may help lower blood pressure and reduce LDL cholesterol levels, though there is a concern about the quality of the supporting data.
Forage
Forage legumes are of two broad types. Some, like alfalfa, clover, vetch, stylo, or Arachis, are sown in pasture and grazed by livestock. Other forage legumes such as Leucaena or Albizia are woody shrub or tree species that are either broken down by livestock or regularly cut by humans to provide livestock feed. Legume based feeds improve animal performance compared to a diet of perennial grasses. Factors attributed towards this: larger consumption, quicker rate of digestion and feed conversion rate efficiency.The type of crop grown or animal rearing will be dependent on the farming system, either vegetables, tubers, grains, cattle etc. In cattle rearing, legume trees such as Gliricidia sepium can be planted along edges of field to provide shade for cattle, the leaves and bark are often eaten by cattle. Green manure can also be grown between periods when crops of economic importance are harvested prior to the next crops to be planted.
Other uses
Legume species grown for their flowers include lupins, which are farmed commercially for their blooms as well as being popular in gardens worldwide. Industrially farmed legumes include Indigofera and Acacia species, which are cultivated for dye and natural gum production, respectively. Fallow/green manure legume species are cultivated to be tilled back into the soil in order to exploit the high levels of captured atmospheric nitrogen found in the roots of most legumes. Numerous legumes farmed for this purpose include Leucaena, Cyamopsis, and Sesbania species. Various legume species are farmed for timber production worldwide, including numerous Acacia species and Castanospermum australe.Legume trees like the locust trees or the Kentucky coffeetree can be used in permaculture food forests. Other legume trees like laburnum and the woody climbing vine wisteria are poisonous.
Classification
recognizes 11 primary pulses. The FAO notes that the term "pulses" is limited to legumes harvested solely for dry grain, thereby excluding legumes that are harvested green for food which are classified as vegetable crops. Also excluded are those legumes used mainly for oil extraction or used exclusively for sowing purposes.- Dry beans
- * Kidney bean, navy bean, pinto bean, black turtle bean, haricot bean
- * Lima bean, butter bean
- * Adzuki bean, azuki bean
- * Mung bean, golden gram, green gram
- * Black gram, urad
- * Scarlet runner bean
- * Ricebean
- * Moth bean
- * Tepary bean
- Dry broad beans
- * Horse bean
- * Broad bean
- * Field bean
- Dry peas
- * Garden pea
- * Protein pea
- Chickpea, garbanzo, Bengal gram
- Dry cowpea, black-eyed pea, blackeye bean
- Pigeon pea, Arhar/Toor, cajan pea, Congo bean, gandules
- Lentil
- Bambara groundnut, earth pea
- Vetch, common vetch
- Lupins
- Pulses NES, Minor pulses, including:
- * Lablab, hyacinth bean
- * Jack bean, sword bean
- * Winged bean
- * Velvet bean, cowitch
- * Yam bean
Pollination
Some tropical legumes that are closely self-pollinated are: Macroptilium atropurpureum 'Siratro', Macroptilum lathyroides, Centrosema pubescens, Neonotonia wightii, and Lotononis bainesii. However, the autogamous annual Stylosanthes humilis proved otherwise by adapting in response to changing conditions during an experiment, and was found to be composed of several genotypes showing heterogeneity.
Two legumes used for pasture with cross-pollination are: Desmodium intortum and Desmodium uncinatum. When the flower is opened, this is the only time fertilization will take place. These two species' characteristics vary in morphology and ruggedness.
Nitrogen fixation
Many legumes contain symbiotic bacteria called Rhizobia within root nodules of their root systems. These bacteria have the special ability of fixing nitrogen from atmospheric, molecular nitrogen into ammonia. The chemical reaction is:Ammonia is then converted to another form, ammonium, usable by plants by the following reaction:
This arrangement means that the root nodules are sources of nitrogen for legumes, making them relatively rich in plant proteins. All proteins contain nitrogenous amino acids. Nitrogen is therefore a necessary ingredient in the production of proteins. Hence, legumes are among the best sources of plant protein.
When a legume plant dies in the field, for example following the harvest, all of its remaining nitrogen, incorporated into amino acids inside the remaining plant parts, is released back into the soil. In the soil, the amino acids are converted to nitrate, making the nitrogen available to other plants, thereby serving as fertilizer for future crops.
In many traditional and organic farming practices, crop rotation involving legumes is common. By alternating between legumes and non-legumes, sometimes planting non-legumes two times in a row and then a legume, the field usually receives a sufficient amount of nitrogenous compounds to produce a good result, even when the crop is non-leguminous. Legumes are sometimes referred to as "green manure".
Sri Lanka developed the farming practice known as coconut-soybean intercropping. Grain legumes are grown in coconut '' groves in two ways: intercropping or as a cash crop. These are grown mainly for their protein, vegetable oil and ability to uphold soil fertility. However, continuous cropping after 3–4 years decrease grain yields significantly.
Distribution and production
Legumes are widely distributed as the third-largest land plant family in terms of number of species, behind only the Orchidaceae and Asteraceae, with about 751 genera and some 19,000 known species, constituting about seven percent of flowering plant species.In 2017, India was the largest producer of pulses with 23% of the world total and also largest importer of pulses in the world. Other major producers were Poland, the United Kingdom, and Mozambique.
Storage
Seed viability decreases with longer storage time. Studies done on Vetch, Horse beans, and peas show that they last about 5 years in storage. Environmental factors that are important in influencing germination are relative humidity and temperature. Two rules apply to moisture content between 5 and 14 percent: the life of the seed will last longer if the storage temperature is reduced by 5 degree Celsius. Secondly, the storage moisture content will decrease if temperature is reduced by 1 degree Celsius.Pests and diseases
A common pest of grain legumes that is noticed in the tropical and subtropical Asia, Africa, Australia and Oceania are minuscule flies that belong to the family Agromyzidae, dubbed "bean flies". They are considered to be the most destructive. The host range of these flies is very wide amongst cultivated legumes. Infestation of plants starts from germination through to harvest, and they can destroy an entire crop in early stage. Black bean aphids are a serious pest to broad beans and other beans. Common hosts for this pest are fathen, thistle and dock. Pea weevil and bean weevil damage leaf margins leaving charactteristics semi-circular notches. Stem nematodes are very widespread but will be found more frequently in areas where host plants are grown.Common legume diseases include anthracnose, caused by Colletotrichum trifolii; common leaf spot caused by Pseudomonas syringae pv. syringae; crown wart caused by Physoderma alfalfae; downy mildew caused by Peronospora trifoliorum; fusarium root rot caused by Fusarium spp.; rust caused by Uromyces striatus; sclerotina crown and stem rot caused by Sclerotinia trifoliorum; Southern blight caused by Sclerotium rolfsii; pythium root rot caused by Pythium spp.; fusarium wilt caused by Fusarium oxysporum; root knot caused by Meloidogyne hapla. These are all classified as biotic problems.
Abiotic problems include nutrient deficiencies,, pollutants, toxic concentration of minerals, and unfavorable growth conditions.