What defines a legume in botanical and agricultural terms?

Legumes are plants belonging to the pea family, Fabaceae (or Leguminosae), or their fruits and seeds. When the seeds are used as dry grain for human consumption, they are also called pulses. This broad category of plants is agriculturally significant for human consumption, livestock forage, silage, and as green manure to improve soil.

What are the primary agricultural uses of legumes?

Legumes are cultivated primarily for human consumption, but also serve as livestock forage and silage. Additionally, they are used as soil-enhancing green manure, contributing to sustainable agricultural practices.

What is the unique botanical structure of a legume's fruit?

Legumes produce a botanically unique type of fruit called a legume. This is a simple, dry fruit that develops from a single carpel and typically dehisces, meaning it splits open along two seams.

How do most legumes contribute to soil fertility through nitrogen fixation?

Most legumes host symbiotic bacteria called Rhizobia within structures in their root systems known as root nodules. These bacteria possess the ability to fix atmospheric nitrogen (N2) into ammonia (NH3), a form that plants can utilize, thereby enriching the soil.

What is the chemical reaction for nitrogen fixation by Rhizobia in legumes?

The chemical reaction for nitrogen fixation by Rhizobia is N2 + 8 H+ + 8 e- → 2 NH3 + H2. The ammonia produced is then converted to ammonium (NH4+), which can be absorbed by plants.

How does nitrogen fixation benefit the legume plant itself?

The nitrogen fixed by Rhizobia bacteria is converted into ammonia and then ammonium, which are usable by the plant. This makes legumes relatively rich in nitrogenous amino acids and protein, essential components for plant growth.

What happens to the nitrogen fixed by legumes when the plant dies, and how does it benefit future crops?

When a legume plant dies, the nitrogen incorporated into its organic matter, such as amino acids, is released back into the soil. In the soil, these compounds are converted into nitrate (NO3-), which then becomes available as a natural fertilizer for subsequent crops.

How is the nitrogen-fixing capability of legumes utilized in farming practices?

The nitrogen-fixing ability of legumes is commonly utilized in farming through crop rotation or polyculture. By alternating legumes with non-legumes or growing them together, farmers can naturally replenish soil nitrogen levels, reducing the need for synthetic nitrogen fertilizers.

What is the practice of using legumes as green manure?

Green manure involves cultivating legume species and then tilling them back into the soil before they set seed. This practice effectively incorporates the captured atmospheric nitrogen and organic matter from the legume roots and plant material into the soil, improving its fertility and structure.

How does the Food and Agriculture Organization (FAO) define the term 'pulse'?

According to the FAO, the term 'pulse' is specifically reserved for legume crops that are harvested solely for their dry seeds. This definition distinguishes them from other legume uses.

What types of legume crops are excluded from the FAO's definition of 'pulse'?

The FAO excludes green beans and green peas, which are considered vegetable crops, from its definition of pulses. Additionally, seeds primarily grown for oil extraction, such as soybeans and peanuts, and those used exclusively for forage, like clovers and alfalfa, are also excluded.

Does common usage always align with the FAO's strict definition of 'pulse'?

No, in common usage, the distinctions made by the FAO are not always strictly followed. Many varieties used for dried pulses are also consumed as green vegetables, and the terms are sometimes used more broadly.

What are some examples of dry beans recognized by the FAO?

The FAO recognizes several types of dry beans, including kidney beans, navy beans, pinto beans, black turtle beans, and haricot beans, which are all varieties of *Phaseolus vulgaris*. Other recognized dry beans include lima beans (*Phaseolus lunatus*), adzuki beans (*Vigna angularis*), mung beans (*Vigna radiata*), black gram (*Vigna mungo*), scarlet runner beans (*Phaseolus coccineus*), ricebeans (*Vigna umbellata*), moth beans (*Vigna aconitifolia*), and tepary beans (*Phaseolus acutifolius*).

Which legumes are specifically classified as dry peas by the FAO?

The FAO classifies garden peas (*Pisum sativum* var. *sativum*) and protein peas (*Pisum sativum* var. *arvense*) as dry peas.

How does the Fabaceae family rank in terms of species diversity among land plants?

The Fabaceae family is the third-largest land plant family in terms of the number of species. It is surpassed only by the Orchidaceae (orchids) and Asteraceae (daisy family) families.

Approximately how many genera and species are estimated to be in the Fabaceae family?

The Fabaceae family is estimated to contain about 751 genera and approximately 19,000 known species, representing about seven percent of all flowering plant species.

What is the role of Rhizobia bacteria in legume root nodules?

Rhizobia bacteria residing in legume root nodules are crucial for nitrogen fixation. They convert atmospheric nitrogen gas (N2) into ammonia (NH3), a process essential for producing amino acids and proteins.

What happens to the nitrogen fixed by legumes when the plant dies, and how does it benefit future crops?

When a legume plant dies, the nitrogen it has fixed is released back into the soil as organic compounds, such as amino acids. These compounds are then converted into nitrates by soil microbes, making the nitrogen available as a natural fertilizer for subsequent crops.

What is the practice of using legumes as green manure?

Green manure involves planting legumes and then incorporating them into the soil while they are still green. This process enriches the soil with nitrogen and organic matter, improving its fertility and structure for future crops.

What family of flies is known as 'bean flies' and considered a significant pest of grain legumes?

The family Agromyzidae, commonly referred to as 'bean flies,' is considered a highly destructive pest of grain legumes. These minuscule flies are found in tropical and subtropical regions of Asia, Africa, Australia, and Oceania, and can infest plants from germination through harvest.

What are some common pests that affect broad beans and other beans?

Common pests affecting legumes include black bean aphids, which are particularly harmful to broad beans, and various species of weevils, such as the pea weevil and bean weevil, which damage leaf margins.

What damage do pea weevils and bean weevils cause to legumes?

Pea weevils and bean weevils typically damage the leaf margins of legume plants, leaving characteristic semi-circular notches.

What are stem nematodes and where are they typically found?

Stem nematodes are microscopic roundworms that are very widespread and can affect various plants, including legumes. They are more frequently encountered in areas where their host plants are cultivated.

Can you list some common fungal and bacterial diseases that affect legumes?

Common legume diseases include anthracnose (*Colletotrichum trifolii*), common leaf spot (*Pseudomonas syringae* pv. *syringae*), crown wart (*Physoderma alfalfae*), downy mildew (*Peronospora trifoliorum*), root rot (*Fusarium* spp.), rust (*Uromyces striatus*), crown and stem rot (*Sclerotinia trifoliorum*), Southern blight (*Sclerotium rolfsii*), pythium root rot (*Pythium* spp.), and fusarium wilt (*Fusarium oxysporum*).

What are some examples of abiotic problems that can affect legume crops?

Abiotic problems affecting legumes include nutrient deficiencies (such as lack of nitrogen, phosphorus, potassium, copper, magnesium, manganese, boron, or zinc), damage from pollutants in air, water, or soil, injury from pesticides, fertilizer burn, and unfavorable growth conditions due to mineral concentrations or environmental factors.

How do temperature and moisture content relate to seed longevity in storage?

For legume seeds with a moisture content between 5% and 14%, reducing the storage temperature by 5 degrees Celsius can double the seed's life. Additionally, reducing the storage temperature by 1 degree Celsius also decreases the seed's moisture content.

For what primary purposes are grain legumes cultivated for human consumption?

Grain legumes are cultivated for their seeds, which are used as food for both humans and animals. They are also a source of oils used for industrial applications.

What role do legumes play in the market for plant-based protein sources?

Legumes are increasingly important as a key ingredient in vegan meat and dairy substitutes. They are growing in popularity as a versatile and sustainable plant-based protein source in the global marketplace.

What is a common misconception about cooking legumes with salt, and what is the reality?

A common misconception is that adding salt before cooking prevents legumes from softening properly. In reality, salting legumes before cooking can actually improve their seasoning, and they may fail to soften due to age, hard water, or acidic ingredients in the cooking pot, rather than the salt itself.

What are the key nutritional components found in legumes?

Legumes are a significant source of protein, dietary fiber, carbohydrates, and various dietary minerals. They are also an excellent source of resistant starch.

What specific nutrients are legumes a significant source of, using chickpeas as an example?

A 100-gram serving of cooked chickpeas provides substantial amounts of key nutrients. It contains about 18% of the Daily Value (DV) for protein, 30% DV for dietary fiber, 43% DV for folate, and 52% DV for manganese.

What is resistant starch, and how does it benefit the human digestive system?

Resistant starch is a type of carbohydrate found in legumes that resists digestion in the small intestine. Instead, it is fermented by bacteria in the large intestine, producing short-chain fatty acids like butyrate, which serve as a vital energy source for intestinal cells.

What are the two main types of forage legumes?

Forage legumes are broadly categorized into two types: those sown in pastures for grazing by livestock, such as alfalfa, clover, and vetch; and those that are woody shrubs or trees, like *Leucaena* and *Albizia*, which are either browsed by livestock or cut by humans for fodder.

How do legume-based feeds improve animal performance compared to perennial grasses?

Legume-based feeds enhance animal performance by leading to larger feed consumption, faster digestion, and a higher feed conversion rate compared to diets consisting solely of perennial grasses.

How can legume trees be utilized in cattle farming?

Legume trees, such as *Gliricidia sepium*, can be planted along field edges to provide shade for cattle. Additionally, cattle may consume the leaves and bark of these trees, providing a supplementary food source.

Which legume is specifically mentioned as being commercially farmed for its flowers?

Lupins are a type of legume that is farmed commercially for their blooms and are also popular ornamental plants in gardens worldwide.

What industrial products are derived from *Indigofera* and *Acacia* species, respectively?

Species from the *Indigofera* genus are cultivated for dye production, while species from the *Acacia* genus are grown for the production of natural gum.

What is the purpose of cultivating 'fallow' or 'green manure' legume species?

Legume species grown as fallow or green manure are cultivated to be tilled back into the soil. This practice leverages the high levels of captured atmospheric nitrogen found in their roots to enrich the soil.

Which legume species are commonly farmed as green manure?

Several legume species are commonly farmed for use as green manure, including *Leucaena*, *Cyamopsis*, and *Sesbania* species.

Which legume species are cultivated for timber production?

Various legume species are farmed for timber worldwide, including numerous species of *Acacia* and *Castanospermum australe*.

What are some examples of legume trees that can be used in agroforestry?

Legume trees like the honey locust (*Gleditsia*) can be incorporated into agroforestry systems, which integrate trees and shrubs into farming landscapes.

Which legume species are noted for having poisonous elements?

Several legume species possess poisonous elements, including the black locust (*Robinia pseudoacacia*), Kentucky coffeetree (*Gymnocladus dioicus*), *Laburnum*, and the woody climbing vine *Wisteria*.

When did Neanderthals and early modern humans begin using wild pulses?

Neanderthals and early modern humans utilized wild pulses in their cooking approximately 70,000 to 40,000 years ago.

What archaeological evidence exists for pulse production in the Indus Valley Civilization?

Traces of pulse production have been discovered around the Ravi River in the Punjab region, which was the center of the Indus Valley Civilization, dating back to approximately 3300 BCE.

Where have traces of lentil cultivation been found in ancient contexts?

Evidence of lentil cultivation has been found within Egyptian pyramids and in ancient cuneiform recipes, indicating their use in those early civilizations.

What is the earliest known archaeological evidence for dry pea cultivation?

Dry pea seeds discovered in a Swiss village, believed to date back to the Stone Age, represent the earliest known archaeological evidence for dry pea cultivation.

When and where is the domestication of the soybean believed to have occurred?

The soybean is believed to have been domesticated in China approximately 5,000 years ago, originating from a wild vine species known as *Glycine soja*.

Where were the oldest domesticated beans in the Americas found, and when?

The oldest known domesticated beans in the Americas were discovered at the Guitarrero Cave archaeological site in Peru. These findings date back to around the second millennium BCE.

What does genetic analysis suggest about the origin and spread of the common bean (*Phaseolus vulgaris*)?

Genetic analyses indicate that the common bean (*Phaseolus vulgaris*) originated in Mesoamerica. From there, it spread southward, often alongside other traditional companion crops like maize and squash.

When and by whom was the domesticated soybean introduced to the United States?

The domesticated soybean was introduced to the United States in 1770 by Benjamin Franklin, who sent seeds to Philadelphia after obtaining them from France.

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What is a Legume?

Botanical Definition

Legumes are plants belonging to the pea family, Fabaceae (also known as Leguminosae). The term also refers to the characteristic fruit or seeds produced by these plants. Botanically, their fruit is a unique, simple, dry fruit that typically dehisces along two seams, known as a legume or pod.^[1]

Agricultural Significance

Agriculturally, legumes are cultivated extensively for various purposes. Primarily, they serve as a vital food source for humans, but they are also crucial as livestock forage, for producing silage, and as green manure to enhance soil fertility.^[1]

Seeds as Pulses

When the seeds of legume plants are harvested for dry consumption, they are specifically referred to as pulses. This category excludes fresh legumes like green beans and peas, as well as seeds primarily used for oil extraction (e.g., soybeans, peanuts) or exclusively for forage (e.g., clovers, alfalfa).^[1]

Terminology: Pulses vs. Legumes

FAO Classification

The United Nations' Food and Agriculture Organization (FAO) defines a pulse narrowly as a legume crop harvested solely for its dry seed. This definition distinguishes them from vegetables (like green peas) and oilseeds (like soybeans).^[1]

The FAO recognizes 11 primary categories of pulses:

Dry beans (e.g., Kidney, Pinto, Black Turtle, Lima)
Dry broad beans
Dry peas
Chickpea (Garbanzo bean)
Dry cowpea (Black-eyed pea)
Pigeon pea
Lentil
Bambara groundnut
Vetch
Lupins
Pulses Not Elsewhere Specified (NES), including Lablab, Jack bean, Winged bean, etc.

^[7]^[8]^[9]^[10]^[11]^[12]^[13]^[14]^[15]^[16]^[17]

Common Usage

In everyday language, the distinction between pulses and other legumes is often blurred. Many varieties used as dried pulses are also consumed as fresh vegetables when their pods are young. Some plants in the Fabaceae family, like certain types of broom, are leguminous but not typically called "legumes" by farmers, who reserve the term for food crops.^[4]^[5]

Global Distribution

Botanical Diversity

The Fabaceae family is remarkably widespread, ranking as the third-largest family of land plants in terms of species diversity. It comprises approximately 751 genera and an estimated 19,000 known species, representing about 7% of all flowering plant species globally.^[7]^[8]^[9]^[10]

Ecological Contributions: Nitrogen Fixation

Symbiotic Partnership

A defining ecological characteristic of most legumes is their symbiotic relationship with nitrogen-fixing bacteria, primarily Rhizobia. These bacteria reside in specialized structures on the plant's roots called root nodules.^[11]

The Nitrogen Cycle

Through this symbiosis, atmospheric nitrogen (N₂) is converted into ammonia (NH₃) and subsequently ammonium (NH₄⁺), forms usable by plants. This process is fundamental to the nitrogen cycle, enriching the soil and making nitrogen available for plant growth.^[11] The chemical reaction is:

N₂ + 8 H⁺ + 8 e⁻ → 2 NH₃ + H₂

This biological nitrogen fixation significantly reduces the need for synthetic nitrogen fertilizers in agriculture.^[12]^[13]

Soil Fertility and Crop Rotation

When legume plants die or are tilled into the soil (as green manure), the fixed nitrogen is released, acting as a natural fertilizer for subsequent crops. This makes legumes invaluable in crop rotation systems, improving soil structure and fertility without external inputs.^[13]^[14]

Common Pests and Diseases

Insect Pests

Legume crops are susceptible to various insect pests, particularly in tropical and subtropical regions. Minute flies from the family Agromyzidae, known as "bean flies," are among the most destructive, affecting plants from germination to harvest. Other significant pests include black bean aphids, pea weevils, and bean weevils, which can damage foliage and reduce yields.^[16]^[17]

Pathogenic Diseases

A range of fungal and bacterial pathogens can affect legumes, leading to diseases such as anthracnose (e.g., Colletotrichum trifolii), common leaf spot (Pseudomonas syringae pv. syringae), root rots (Fusarium spp., Pythium spp.), and wilts (Fusarium oxysporum).^[18]

Abiotic Factors

Beyond biotic factors, legumes can suffer from abiotic problems. These include nutrient deficiencies (e.g., nitrogen, phosphorus, potassium), toxicity from mineral concentrations, and adverse environmental conditions such as pollutants or unfavorable soil pH.^[19]

Seed Storage and Viability

Longevity Factors

The viability of legume seeds decreases over time. Studies indicate that seeds like vetch, broad beans, and peas typically maintain viability for about 5 years under optimal storage conditions. Key environmental factors influencing germination and longevity are relative humidity and temperature.^[20]

Optimal Conditions

To maximize seed life, two principles apply regarding moisture content (between 5% and 14%): reducing storage temperature by 5°C approximately doubles the seed's lifespan. Furthermore, lowering the temperature by 1°C reduces the required storage moisture content, further preserving viability.^[20]

Diverse Applications of Legumes

Human Consumption

Legumes are a cornerstone of global diets, valued for their seeds, which are rich sources of protein, dietary fiber, complex carbohydrates, and essential minerals like folate and manganese. They are increasingly utilized as plant-based protein sources in meat and dairy alternatives, reflecting a growing market trend.^[21]^[23]^[24]

A 100-gram serving of cooked chickpeas, for example, provides significant amounts of key nutrients:

Protein: 18% of Daily Value (DV)
Dietary Fiber: 30% DV
Folate: 43% DV
Manganese: 52% DV

Legumes are also excellent sources of resistant starch, which benefits gut health by being fermented into short-chain fatty acids by intestinal bacteria.^[28]^[29]

Forage for Livestock

Forage legumes, such as alfalfa, clover, and vetch, are vital components of pastures and animal feed. They are grazed directly by livestock or harvested as fodder. Legume-based feeds are known to improve animal performance by enhancing consumption, digestion, and feed conversion rates compared to diets solely based on perennial grasses.^[30]

White clover (*Trifolium repens*), a common forage legume.

Other Industrial and Ecological Uses

Beyond food and feed, legumes serve numerous other purposes. Species like lupins are cultivated for ornamental blooms. Industrially, plants such as Indigofera are sources for dyes, and Acacia species yield natural gums. Many legumes are also grown specifically to be tilled back into the soil as green manure, leveraging their nitrogen-fixing capabilities to enrich the land for future crops.^[31] Some species, like honey locust and black locust, are utilized in agroforestry or for timber.^[32]^[33]

Historical Significance

Ancient Cultivation

The use of pulses by humans dates back tens of thousands of years, with evidence suggesting Neanderthals and early modern humans consumed them. Archaeological findings indicate pulse cultivation around the Ravi River (Indus Valley) by 3300 BCE, and lentil cultivation was present in ancient Egypt and Mesopotamia.^[36]^[37]

Global Domestication

Dry pea seeds found in Swiss Stone Age settlements suggest cultivation in the eastern Mediterranean and Mesopotamia at least 5,000 years ago. The soybean was domesticated in China around the same period. In the Americas, domesticated beans were found in Peru dating to the second millennium BCE, with genetic studies tracing their origin to Mesoamerica.^[38]^[39]^[40]^[41]

International Year of Pulses

Global Recognition

The United Nations declared 2016 the International Year of Pulses (IYP). This initiative, facilitated by the Food and Agriculture Organization (FAO), aimed to raise global awareness about the nutritional benefits of pulses and their role in sustainable food systems and food security.^[43]

Objectives of IYP

The IYP sought to encourage better utilization of pulse-based proteins, boost global production, promote crop rotations involving legumes, and address challenges in the international trade of pulses. It provided a platform to connect stakeholders across the food chain.^[43]^[44]

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References

FAOSTAT code 0176, Phaseolus spp. including several species now in Vigna.

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The Verdant Bounty

💡 Dive in with Flashcard Learning! 💡

What is a Legume? ℹ️

🌱 Botanical Definition

🌾 Agricultural Significance

🍽️ Seeds as Pulses

Terminology: Pulses vs. Legumes 📚

⚖️ FAO Classification

🗣️ Common Usage

Global Distribution 🌍

🌳 Botanical Diversity

Ecological Contributions: Nitrogen Fixation 🔬

🤝 Symbiotic Partnership

⚡ The Nitrogen Cycle

🔄 Soil Fertility and Crop Rotation

Common Pests and Diseases 🐞

🐛 Insect Pests

🦠 Pathogenic Diseases

🌡️ Abiotic Factors

Seed Storage and Viability 📦

⏳ Longevity Factors

❄️ Optimal Conditions

Diverse Applications of Legumes 💡

🍽️ Human Consumption

🐄 Forage for Livestock

🎨 Other Industrial and Ecological Uses

Historical Significance 📜

⏳ Ancient Cultivation

🌍 Global Domestication

International Year of Pulses 🗓️

🇺🇳 Global Recognition

📈 Objectives of IYP

Teacher's Corner 🧑‍🏫

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📜 Important Notice

Dive in with Flashcard Learning!

What is a Legume?

Botanical Definition

Agricultural Significance

Seeds as Pulses

Terminology: Pulses vs. Legumes

FAO Classification

Common Usage

Global Distribution

Botanical Diversity

Ecological Contributions: Nitrogen Fixation

Symbiotic Partnership

The Nitrogen Cycle

Soil Fertility and Crop Rotation

Common Pests and Diseases

Insect Pests

Pathogenic Diseases

Abiotic Factors

Seed Storage and Viability

Longevity Factors

Optimal Conditions

Diverse Applications of Legumes

Human Consumption

Forage for Livestock

Other Industrial and Ecological Uses

Historical Significance

Ancient Cultivation

Global Domestication

International Year of Pulses

Global Recognition

Objectives of IYP

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice