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Legume

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Legumes are plants belonging to the Fabaceae family, also known as Leguminosae.

Various legumes
Various legumes

This family is the third largest land plant group, following only the Orchidaceae and Asteraceae. It contains approximately 751 genera and 19,000 known species. Legumes are unique because they produce a specific type of fruit. This is a simple dry fruit that develops from a single carpel. Most of these fruits dehisce, which means they open along a seam on two sides. While many people use the term "legume" generally, certain specialized terms exist. When legume seeds are harvested solely for dry grain consumption, they are called pulses.

Pulse in Nanglo
Pulse in Nanglo

A defining feature of most legumes is their ability to perform nitrogen fixation. This process relies on a symbiotic relationship with bacteria called Rhizobia. These bacteria live inside small structures on the plant's roots called root nodules.

Soil fertility - nitrogen fixation by root nodules on Wistaria roots, with hazelnut to show size
Soil fertility - nitrogen fixation by root nodules on Wistaria roots, with hazelnut to show size

The Rhizobia take molecular nitrogen (N2) from the atmosphere and convert it into ammonia (NH3). This ammonia is then converted into ammonium, which the plant can use. Because nitrogen is a necessary ingredient for producing proteins, this process makes legumes very rich in nitrogenous amino acids. This biological mechanism allows legumes to thrive even in soils where nitrogen might be limited.

This nitrogen-fixing ability has massive implications for agriculture and the nitrogen cycle.

Nitrogen Cycle
Nitrogen Cycle

When a legume plant dies after harvest, its remaining nitrogen is released back into the soil. In the soil, these amino acids are converted into nitrate, which becomes available for future crops. Because of this, farmers often use legumes in crop rotation or polyculture. By alternating legumes with non-legumes, farmers can replenish soil fertility without needing extra nitrogenous fertilizer. Some farmers even use legumes as "green manure." This involves growing the plants and then tilling them directly back into the soil to exploit the captured nitrogen. In Sri Lanka, a specific practice called coconut-soybean intercropping is used in coconut groves to uphold soil fertility.

The variety of legumes available for human use is vast. The Food and Agriculture Organization (FAO) recognizes 11 primary pulses. These include various dry beans like kidney beans, navy beans, and pinto beans. Other important pulses include lentils, chickpeas, and various types of peas. There are also many types of cowpeas, such as the black-eyed pea, and various mung beans. It is important to note that the FAO excludes certain plants from the "pulse" category. This includes green vegetables like green peas, oilseeds like soybeans and peanuts, and forage crops like clover or alfalfa. While these are all legumes, they serve different economic and nutritional purposes.

Legumes are incredibly nutritious for the human diet. They are a significant source of protein, dietary fiber, carbohydrates, and minerals. For example, a 100-gram serving of cooked chickpeas provides 18 percent of the Daily Value (DV) for protein. It also provides 30 percent DV for dietary fiber, 43 percent DV for folate, and 52 percent DV for manganese. Furthermore, legumes are an excellent source of resistant starch. This type of starch is broken down by bacteria in the large intestine to produce short-chain fatty acids, such as butyrate. These fatty acids are used by intestinal cells for energy. Because of this high protein content, legumes are increasingly used as plant-based meat and dairy substitutes.

Humans have been interacting with these plants for tens of thousands of years. Archaeological evidence shows that Neanderthals and early modern humans used wild pulses for meals between 70,000 and 40,000 years ago. Evidence of lentil cultivation has been found in Egyptian pyramids and ancient cuneiform recipes. The soybean was domesticated in China about 5,000 years ago from the wild vine Glycine soja. In the Americas, the oldest domesticated beans were found in Guitarrero Cave in Peru. Even the soybean was introduced to the United States in 1770 by Benjamin Franklin. This long history shows how central legumes have been to human survival and development.

Beyond food, legumes serve many industrial and ecological roles. Some species, like lupins, are grown commercially for their beautiful flowers.

Flower garden in Ushuaia (5542996965)
Flower garden in Ushuaia (5542996965)

Others, such as Indigofera and Acacia, are used for dye and natural gum production. Some legumes are even used for timber production. However, farmers must protect these crops from various threats. Pests like "bean flies" (Agromyzidae) and black bean aphids can destroy entire crops. Plants also face "biotic" problems like diseases such as rust or root rot, and "abiotic" problems like nutrient deficiencies or pollutants. Managing these factors is essential for maintaining the global supply of these versatile plants.

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🖼️ Images & Media (8)
File:Various legumes.jpg
Various legumes.jpg
File:Soil fertility - nitrogen fixation by root nodules on Wistaria roots, with hazelnut to show size.JPG
Soil fertility - nitrogen fixation by...
File:Nitrogen Cycle.jpg
Nitrogen Cycle.jpg
File:Pulse in Nanglo.jpg
Pulse in Nanglo.jpg
File:Peanut 9417.jpg
Peanut 9417.jpg
File:TrifoliumRepensFlowers.jpg
TrifoliumRepensFlowers.jpg
File:Flower garden in Ushuaia (5542996965).jpg
Flower garden in Ushuaia (5542996965).jpg
File:Pulses for Sale in Market - Darjeeling - West Bengal - India (12431603075).jpg
Pulses for Sale in Market - Darjeeling -...
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