# Legumes crops: A builders of soil fertility through nitrogen fixation

Sunita Kumari Meena, Ajeet Kumar, Navnit Kumar, Lalita Rana

► To cite this version:

Sunita Kumari Meena, Ajeet Kumar, Navnit Kumar, Lalita Rana. Legumes crops: A builders of soil fertility through nitrogen fixation. A. Kumar, N. Kumar, G. Kumar, G. Kumari, L. Rana, S.K. Sahoo. Agrobios Research, 1 (1), pp.107-128, 2022, 978-93-94380-08-0. hal-04881441

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# 8. Legume Crops: A Builders of Soil Fertility through Nitrogen Fixation

SUNITA KUMARI MEENA, AJEET KUMAR, NAVNIT KUMAR AND LALITA RANA

Nitrogen is frequently a limiting nutrient in agricultural systems, and despite being abundant in the atmosphere, only limited reserves of soil inorganic nitrogen, primarily in the form of nitrate and ammonium, are accessible to plants. As a result, nitrogen availability frequently limits agricultural yields. For centuries, crop rotation or co-culture with legumes, as well as the use of fertilizers such as animal waste, wood ash, or seaweed, have been used to combat this limitation. At the turn of the twentieth century, two German chemists, Fritz Haber and Carl Bosch, invented a process for industrial-scale nitrogen fixation, or the conversion of di-nitrogen into ammonium (Peoples et al., 1995 and Erisman et al., 2008).

The use of synthetic fertilizers was a key role in dramatically increasing food production during the Green Revolution, particularly in developing nations, and over half of the world's population now relies on them for their survival. Breaking the triple bonds of di-nitrogen needs enormous amounts of energy (1-2% of world energy supply), and one tone of natural gas is used to make one tone of synthetic nitrogen fertilizers. Fertilizer prices are, unsurprisingly, greatly influenced by the price of natural gas. However, the reliance on natural gas, a scarce resource, for so much food production is worrying. Paradoxically, biofuel production is reliant on synthetic fertilizers and so fossil fuels, defeating the fundamental aim of biofuels. All of these examples demonstrate that crop nitrogen availability is a threat to our farming production, economics, and food security (Vania et al., 2019).

The effectiveness of legumes to prevent erosion, reduce weeds, and add organic matter to the soil varies greatly. Legumes do not scavenge nitrogen as effectively as grasses. A grass, brassica, or a mixture is usually a preferable choice for a cover crop to absorb extra nutrients following manure or fertilizer treatments. Mixtures of legume and grass cover crops incorporate
the advantages of both, such as biomass production, nitrogen scavenging and additions to the system, weed and erosion control, and more. Legumes can be used by organic farmers to provide significant amounts of nitrogen to soils through biological nitrogen fixation and the incorporation of nitrogen-rich plant biomass. Growing legumes as cover crops may provide additional benefits, such as:

<table><thead><tr><th></th><th>Diversification</th><th>Tiemann et al., 2015</th></tr></thead><tbody><tr><td rowspan="7">Benefits of legumes grown as cover crops</td><td>Stabilization of plant-microbe metabolic cycles</td><td>Blagodatskaya et al., 2014</td></tr><tr><td>Erosion control</td><td>Basche et al., 2016</td></tr><tr><td>Nutrient management</td><td>Bergtold et al., 2012; Finney et al., 2016; Syswerda et al., 2012</td></tr><tr><td>Weed suppression</td><td>Leavitt et al., 2011</td></tr><tr><td>Disruption of pest cycles</td><td>Ratnadass et al., 2012</td></tr><tr><td>Increased water infiltration</td><td>Baumhardt et al., 2015</td></tr><tr><td>Temperature stabilization</td><td>Basche et al., 2016</td></tr></tbody></table>

# 1. SIGNIFICANCE OF LEGUMES

The *Poaceae* (cereals and grasses) and *Fabaceae* (fabrics) plant groups are the most important in world agriculture. There are around 650 genera and 18,000 species in the legume family. Cereals are the most significant in terms of production volume since they provide the carbohydrates that make up the majority of human and animal diets (figure 8.1).

<figure><img src="image_3.png" /><figcaption>FIGURE 8.1: Estimated production of major crops in India 2021-22 (Source: As per the 3rd Advance Estimates, the Union Ministry of Agriculture and Farmers Welfare (2021-22))</figcaption></figure>
Grain legumes not only add variety to the human diet, but they also provide dietary protein for many people who don't eat meat or fish. Grain legumes are generally high in lysine but low in methionine, which complements the reverse amino acid pattern observed in cereals. Furthermore, practically all grain legumes fix their own nitrogen, lowering the cost of nitrogen inputs for farmers in many cases. Grain legumes, particularly soybeans and peanuts, are rich in vegetable oils, which are used to make cooking oil, margarine, mayonnaise, and salad dressings.

## A. Legumes' Prominence: A Gift from Nature for a Healthier Lifestyle and a More Sustainable Future

### Chemical

- Laxative - senna pods (Cassia)

- Insecticide, fish poison - rotenone (Tephrosia), (Derris, Lonchocarpus)

- Resin for paints, lacquers - (Hymenaea, Copaifera)

- Gum - gum arabic (Acacia), guar gum (Cyamopsis)

- Tannin - bark of Acacia

- Dye - indigo (Indigofera)

- Steroids - seed of Glycine "the pill"

### Food

- Spice - fenugreek (Trigonella foenum-graecum)

- Extract - licorice (Glycyrrhiza glabra)

- Seasoning - tamarind (Tamarindus indica)

- Tubers - yam beans (Pachyrhizus, Sphenostylis)

- Flowers, leaves, shoots - winged bean (Psophocarpus tetragonolobus)

- Chocolate substitute - carob (Ceratonia siliqua)

- Starch - tubers of kudzu (Pueraria montana)

- Beverage - alfalfa tea (Medicago sativa)

- Honey - nectar of Trifolium, Medicago, Prosopis

- Grain legumes - peas (Pisum), beans (Phaseolus), lentils (Lens)

- Esthetic value - wisteria (Wisteria), flamboyant (Delonix)

### Others

- Timber - rosewood (Dalbergia)

- Pasture - clovers (Trifolium), alfalfa (Medicago)

- Browse trees and shrubs - koa haole (Leucaena), honey locust (Gleditsia)

- Green manure or soil cover - sunn hemp (Crotalaria), kudzu (Pueraria)

- Green and conserved forage - vetches (Vicia), sweet clovers (Melilotus)

- Ornamental jewelry - rosary pea (Abrus)

- Charcoal - mesquite (Prosopis)
## 2. CLASSIFICATION OF LEGUME CROP

There are 11 different types of pulses recognised by the Food and Agriculture Organization (FAO). According to the FAO (1994), the term “pulses” refers to legumes collected primarily for dry grain, omitting legumes picked green for food (green peas, green beans, etc.), which are categorized as vegetable crops. Also prohibited are legumes grown primarily for oil extraction (e.g., soybeans and groundnuts) or grown solely for seed production (e.g., seeds of clover and alfalfa).

<table><caption>TABLE 8.1: Scientific name, common name and regions of diversity of grain legumes</caption><thead><tr><th>Scientific name</th><th>Common name</th><th>Regions of diversity</th></tr></thead><tbody><tr><td colspan="3"><strong>Primary grain legumes</strong></td></tr><tr><td>Arachis hypogaea L.</td><td>Peanut</td><td>South America</td></tr><tr><td>Cajanus cajan (L.) Millsp.</td><td>Pigeon pea</td><td>India</td></tr><tr><td>Cicer arietinum L.</td><td>Chickpea</td><td>SW Asia, Ethiopia, India</td></tr><tr><td>Glycine max (L.) Merr.</td><td>Soybean</td><td>East Asia</td></tr><tr><td>Lens culinaris Medic.</td><td>Lentil</td><td>SW Asia, Mediterranean</td></tr><tr><td>Phaseolus lunatus L.</td><td>Lima bean</td><td>Peru</td></tr><tr><td>Phaseolus vulgaris L.</td><td>Common bean</td><td>Mexico, Guatemala</td></tr><tr><td>Pisum sativum L.</td><td>Pea</td><td>SW Asia, Mediterranean</td></tr><tr><td>Vicia faba L.</td><td>Faba bean</td><td>Asia, Mediterranean</td></tr><tr><td>Vigna angularis (Willd.) Ohwi & Ohashi</td><td>Adzuki bean</td><td>Japan, China</td></tr><tr><td>Vigna radiate (L.) Wilczek</td><td>Mung bean</td><td>Indi, SE Asia</td></tr><tr><td>Vigna unguiculata (L.) Walp.</td><td>Cowpea</td><td>W. Africa, India</td></tr><tr><td colspan="3"><strong>Secondary grain legumes</strong></td></tr><tr><td>Canavalia ensiformis (L.) DC.</td><td>Jackbean</td><td>Mexico, Southwest US</td></tr><tr><td>Canavalia gladiata (Jacq.) DC.</td><td>Swordbean</td><td>India, Humid Africa</td></tr><tr><td>Cyamopsis tetragonoloba (L.) Taub.</td><td>Guar</td><td>India, Pakistan</td></tr><tr><td>Lablab purpureus (L.) Sweet</td><td>Hyacinth bean</td><td>India</td></tr><tr><td>Lathyrus sativus L.</td><td>Chickling vetch</td><td>India</td></tr><tr><td>Lupinus ssp.</td><td>Lupins</td><td>Europe, Andean Highlands</td></tr><tr><td>Macrotyloma geocarpum (Harms) Marachel & Baudet</td><td>Kersting's groundnut</td><td>Africa</td></tr><tr><td>Phaseolus acutifolius A. Gray</td><td>Tepary bean</td><td>Mexico, Southwest US</td></tr><tr><td>Phaseolus coccineus L.</td><td>Scarlet runner bean</td><td>Central American Highlands</td></tr><tr><td>Psophocarpus tetragonoloba (L.) DC.</td><td>Winged bean</td><td>Papua New Guinea, Southeast Asia</td></tr><tr><td>Vigna aconitifolia (Jacq.) Marechal</td><td>Moth bean</td><td>India</td></tr></tbody></table>
<table><thead><tr><th>Scientific name</th><th>Common name</th><th>Regions of diversity</th></tr></thead><tbody><tr><td>Vigna mungo (L.) Hepper</td><td>Black gram</td><td>Indo-Pakistan subcontinent</td></tr><tr><td>Vigna subterranea (L.) Verdc.</td><td>Bambara groundnut</td><td>Sub-Saharan Africa</td></tr><tr><td>Vigna umbellata (Thumb.) Ohwi & Ohashi</td><td>Rice bean</td><td>South and Southeast Asia</td></tr><tr><th colspan="3">Tertiary grain legumes</th></tr><tr><td>Amphicarpa bracteata (L.) Fem.</td><td>Hog peanut</td><td>North America</td></tr><tr><td>Apios americana Medic.</td><td>Potato bean</td><td>North America</td></tr><tr><td>Cordeauxia edulis Hemsl.</td><td>Ye-eb</td><td>Somalia, Ethiopia</td></tr><tr><td>Macrotyloma uniflorum (Lam.) Verdc.</td><td>Horse gram</td><td>Southern India, Trop. Africa</td></tr><tr><td>Strophostyles helvola (L.) Ell.</td><td>Wild bean</td><td>North America</td></tr><tr><td>Tylosema esculentum (Burchell) Schreiber</td><td>Marama bean</td><td>South Africa</td></tr></tbody></table>

(Source: Hymowitz, 1990)

Grain legumes are plants that are utilised as food, either directly or indirectly, in the form of unripe pods, immature seed, or mature dried seed. The principal grain legumes are made up of twelve crops. They are distinguished by the following characteristics (Table 8.2). The crops are mostly from the Vicieae (Lens, Pisum, Vicia) and Phaseoleae tribes of the Papilionoideae subfamily (Cajanus, Phaseolus, Vigna). Arachis, which is in the Aeschynomeneae, and Cicer, which is now in its own tribe, the Cicereae, are exceptions. The Vicieae are found in the Sino-India region or the Fertile Crescent, while the Phaseoleae are found in the tropics or subtropics. Crops are cultivated all around the world and exchanged in international markets. For each crop, large, complete germplasm collections are maintained. Every one of them has at least one full-time librarian. Cultivars are the result of current plant breeding techniques. These crop's land races are fast dwindling.

The secondary grain legumes guar and lupins are uncommon members of the family. Guar is grown on millions of acres in India, Pakistan, the United States, and worldwide as a source of gum. The seed's gum is extracted and used in the paper, oil well drilling, explosives, and mining sectors, as well as numerous processed food and beverage goods. Guar as a grain legume is only grown in a few parts of India and Pakistan. Because grain legumes are not grown throughout a large geographic area, they are not important in world trade. National germplasm collections for each crop are available, however creators typically work part-time on numerous crops to maintain or manage a given collection. With the exception of guar and lupins, simple selection is the most common plant breeding approach employed for cultivar development. As a result, the line between cultigens and wild forms is frequently blurred.
Land races account for a large amount of total production. *Lupinus albus*, *Lupinus angustifolia*, *Lupinus cosentinii*, *Lupinus luteus*, and *Lupinus mutabilis* are generally used as green manures, fodder crops, and livestock forage. Because the seeds were high in alkaloids, lupins were rarely employed as grain legumes in the past. Cultivars with lower alkaloid content in seed and non-dehiscent fruits have only been created in the last 20-30 years. These are the lupins known as "sweet." In terms of seed protein content, lupins and winged beans are second only to soybeans among grain legumes (28-48 percent depending on species). The utilization of sweet lupins as a human food source has yet to be properly investigated.

Those legume species that are rarely grown outside of their natural habitat are known as tertiary grain legumes. They are not genuine domesticated plants, but rather plants that have been cared for or protected, and whose seed is gathered by the indigenous population primarily during times of environmental crisis. The majority of the data on these plants comes from social scientists, missionaries, or possibly taxonomists performing floristic research. The first obvious step in evaluating the potential of these grain legumes would be to start collecting germplasm.

<table><caption>TABLE 8.2: Seasonal categories of legumes</caption><thead><tr><th>Winter-annual legumes</th><th>Perennial or biennial legumes</th><th>Summer-annual legume</th></tr></thead><tbody><tr><td><ul><li>Planted in the autumn, produce the majority of their biomass and nitrogen in the spring.</li><li>In many areas, must be planted earlier than cereal crops to survive the winter.</li><li>Spring management of legumes will often involve balancing early planting of the cash crop with waiting to allow more biomass and N production by the legume.</li></ul></td><td><ul><li>These fodder crops are commonly planted for a short amount of time between cash crops, but they can also be used for more than one year and are frequently harvested for feed throughout this time.</li><li>They can be planted besides or over seeded into other crops like wheat or oats, then let to grow after the cash crop is harvested and used as feed.</li><li>They are more of a rotation crop than a cover crop here, although they give various benefits such as erosion and weed control, organic matter generation, nitrogen production and disrupt the cycles of weeds, diseases, and insects.</li></ul></td><td><ul><li>These summer annuals provide nitrogen and provide ground cover for weed and erosion management, as well as other cover crop benefits.</li><li>Climate, cropping system, and the legume itself all influence establishment and management.</li><li>In colder climate, summer-annual legume crops include the winter-annual crops listed above, as well as warm-season legumes like cowpeas.</li></ul></td></tr></tbody></table>
A. Nitrogen Fixation - Return of Nitrogen to Soil as-well-as Other Crops

Plenty of the nitrogen that has been fixed is absorbed by the plant. However, some nitrogen can be "leaked" or "transferred" into the soil for non-legume plants (30-50 lb N/acre) (Walley *et al.*, 1996). When the legume's vegetation (roots, leaves, and fruits) dies and decomposes, the majority of the nitrogen is returned to the soil for use by nearby plants. The majority of the nitrogen is eventually returned to the soil for use by nearby plants. Within the root nodules of many legumes' root systems are symbiotic bacteria called Rhizobia (plants belonging to the genus *Styphnolobium* are one exception to this rule). These bacteria have the unique capacity to fix nitrogen from the atmosphere, converting it to ammonia ($NH_3$). The chemical reaction is as follows:

$$N_2 + 8H^+ + 8e^- \rightarrow 2NH_3 + H_2$$

The following reaction converts ammonia to ammonium ($NH_4^+$), which can be used by (some) plants:

$$NH_3 + H^+ \rightarrow NH_4^+$$

Because of this configuration, the root nodules are nitrogen sources for legumes, making them relatively high in plant proteins. Nitrogenous amino acids are found in all proteins. As a result, nitrogen is an essential component in the creation of proteins. As a result, beans are one of the greatest plant protein sources. When a legume plant dies in the field, such as after harvest, all of the leftover nitrogen is absorbed into amino acids and released back into the soil. The amino acids are transformed to nitrate ($NO_3^-$), which makes nitrogen available to other plants and hence serves as fertilizer for future crops, in the soil. Crop rotation using legumes is common in many traditional and organic farming systems. Even when the crop is non-leguminous, the field normally receives enough nitrogenous compounds to give a decent outcome by alternating legumes and non-legumes, sometimes planting non-legumes two times in a row and then a legume. "Green manure" is a term used to describe legumes.

Certain legumes are more effective at nitrogen fixation than others. Beans are poor nitrogen fixers (less than 50 lb N per acre) and fix less nitrogen than they require. Beans in New Mexico require an additional 30-50 pound of nitrogen fertilizer per acre to get maximum economic yield. However, regardless of the amount of nitrogen given, yields are generally low if beans are not nodulated. Nodules appear to aid in the efficient utilization of nitrogen fertilizer by the plant.
Many grain legumes, such as peanuts, cowpeas, soybeans, and faba beans, are nitrogen fixers and will fix all of their nitrogen needs save that which is absorbed from the soil. These legumes may fix up to 250 pounds of nitrogen per acre and are rarely fertilized (Walley *et al.*, 1996). In fact, as long as they are capable of fixing nitrogen, they rarely respond to nitrogen fertilizer. When grown on sandy or poor organic matter soils, nitrogen fertilizer is frequently administered at planting to supply nitrogen to the plant before nitrogen fixation begins. Whenever nitrogen is used, it should be applied at a rate of no more than 15 pounds per acre. When too much nitrogen is administered, the legume's nitrogen fixation process is slowed or stopped entirely (Delwiche and Wijler, 1956). The plant can absorb nitrogen from the soil more easily and with less energy than it can fix nitrogen from the air. Alfalfa, sweet clover, true clovers, and vetches are examples of perennial and forage legumes that may fix 250-500 lb of nitrogen per acre. They are not fertilized with nitrogen in the same way as grain legumes are not. When the photosynthate supply is insufficient for optimal nitrogen fixation, they may respond to nitrogen fertilizer at planting or soon after a cutting (Aranjuelo *et al.*, 2009). In the presence of large quantities of soil N, however, $N_2$ fixation persists, but at a lower rate (Lamb *et al.*, 1995). It's also worth noting that, as compared to non-$N_2$-fixing alfalfa varieties, $N_2$-fixing alfalfa is significantly better at absorbing excess nitrogen from the soil (Russelle *et al.*, 2007).

When a grain legume crop's grain is harvested, only a small amount of nitrogen is returned to the following crop. The majority of the nitrogen fixed in the field over the season is removed as grain. Grain legumes, such as soybeans and beans, have nearly the same amount of nitrogen in their stalks, leaves, and roots as non-legume crop leftovers. In fact, the residue from a corn crop contains more nitrogen than the residue from a bean crop simply because the corn crop produces more residues after harvest. Only if the complete biomass (stems, leaves, and roots) is absorbed into the soil does a perennial or forage legume crop provide sufficient nitrogen for the following crop. When forage is cut and removed from the field, the majority of the nitrogen it fixes is lost. In comparison to aboveground biomass, roots and crowns contribute very little nitrogen to the soil.

### 3. DESCRIPTION OF SOME IMPORTANT LEGUME CROP-

#### A. Berseem Clover (Trifolium alexandrinum)

* Another name: Egyptian clover

* Type: Summer or winter annual legumes
► **Roles:** weed control, erosion prevention, green manure, chopped fodder, and grazing

► **Blend with:** As a nursing crop, combine with oats, ryegrass, and small grains; as an alfalfa nurse crop

- Early in its life cycle, Berseem clover pulls nitrogen from the soil. It can fix 100 to 200 lb. N/acre or more after soil reserves are depleted.

► **Berseem Clover's Attributes:** green manure, biomass, smother crop, Companion crop, quick growing, seed crop, legume nurse crop, grazing and forage crop.

- Drought-resistant although not as much as alfalfa. Some cultivars may withstand higher soil moisture than alfalfa or sweet clover, but not waterlogging.

- The seed size is similar to that of red clover.

- Because its white or ivory flowers do not contain a tripping mechanism, it is bee-friendly.

- Berseem clover does not utilise phosphorus to the same depth as mature, perennial alfalfa because of its small roots.

- Berseem that has been winterkilled can be planted sooner in the spring than winter-hardy annuals. It does not deplete moisture as dead organic mulch, but it may decrease soil warming and drying when compared to erosion-prone bare fallow.

## B. Cowpeas (Vigna unguiculata)

► **Another name:** southern peas, blackeye peas, crowder peas

► **Type:** summer annual legume

► **Roles:** weed control, nitrogen supply, soil improvement, erosion prevention, forage cowpea used as a mulch

- Blend with sorghum-sudangrass hybrid or foxtail hay-type millet; inter-seeded with corn or sorghum.

► **Cowpeas advantage:** weed-smothering biomass, quick green manure, IPM insectary crop, companion crop, seed and feed options, cultivars from diverse niche, low moisture need.

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>
- Cowpeas generate 100 to 150 lbs. N/acre and protect soil from erosion. Although dense residue improves soil texture, it degrades quickly in warmer weather. Cowpeas thrive in temperate climates where summers are warm or hot but frequently dry (drought resilience nature), heat tolerance, low fertility, and adaptability to a variety of soils.

- Cowpeas can withstand drought better than soybeans, although they are less resistant to waterlogging and frost.

### C. Crimson clover (Trifolium incarnatum)

- **Type:** winter or summer annual legume

- **Roles:** N source, soil builder, erosion prevention, reseeding inter-row ground cover, forage

- **Blend with:** rye and other cereals, vetches, annual ryegrass, subclover, red clover, black medic

- **Crimson Clover's Attributes:** nutrient recycler, nitrogen source, biomass, beneficial habitat and nectar source and mixture.

<figure><img src="image_6.png" /></figure>

- Compared to hairy vetch, bigflower vetch, berseem clover, arrowleaf clover (Trifolium vesiculosum), and winter peas, crimson clover produced the greatest dry matter (5,600 to 6,000 lb. /A) in field experiments in Mississippi. Because of its high early-autumn dry matter output, it is suggested for soil erosion management. It generated 99 to 130 lb. N/acre

### D. Field peas (Pisum sativum subsp. arvense)

- **Another name:** Austrian winter peas (black peas), Canadian field peas (spring peas)

- **Type:** summer and winter annual legume

- **Roles:** Plow-down nitrogen source, weed suppressor, and forage

- **Blend with:** For vertical support, combine with strong-stemmed wheat, rye, triticale, or barley

- **Benefits of Field Peas:** nitrogen source, rotational effects, water thrifty, bountiful biomass, seed crop, forage booster, quick growing, long-term bloomer, chill tolerant.

<figure><img src="image_7.png" /></figure>
- Austrian winter peas are excellent nitrogen producers, yielding 90 to 150 lb. N/acre, and even up to 300 lb. N/acre at times.

- Grain legumes provide a soil-protecting alternative to fallow, and they can be managed to keep the cereal crop moist. Long-term benefits of legumes include providing nitrogen for succeeding crops, disrupting disease, insect, and weed cycles, and improving soil quality.

## E. Hairy vetch (Vicia villosa)

- **Type:** winter or summer annual legume

- **Roles:** N source, weed suppressor, topsoil conditioner, reduce erosion

- **Blend with:** small grains, field peas, bell beans, crimson clover, buckwheat

- **Potential N fixed/year:** 50 to 150 lbs./acre

- Few legumes match hairy vetch for spring residue production or nitrogen contribution.

<figure><img src="image_8.png" /></figure>

- Hairy vetch is one of the few legumes that can equal hairy vetch in terms of spring residue yield and nitrogen contribution. In temperate and subtropical climates, hairy vetch is a major source of nitrogen.

- Root development continues throughout the winter but cover grows slowly. Hairy vetch grows quickly in the spring, becoming a sprawling vine up to 12 feet long. Unless the vetch is supported by another crop, the field height rarely reaches 3 feet.

- Its extensive viney biomass can be both a boon and a hindrance. The stand, on the other hand, suffocates spring weeds and can help you replace all or part of your N fertilizer needs for late-planted crops.

- **Benefits of hairy vetch:** nitrogen source, soil conditioner, early weed suppression, good with grains, moisture-thrifty, phosphorus scavenger, fits many systems, widely adapted.

## F. Medics (Medicago spp.)

- **Another name:** black medic, burr (or bur) medic, burclover

- **Type:** Winter or summer annual legume

- **Roles:** N source, soil quality builder, weed suppressor, erosion fighter

<figure><img src="image_9.png" /></figure>
► **Blend with:** Other medics; clovers and grasses; small grains

► **Benefits of medics:** a good source of nitrogen in a low-moisture environment, weed control, raise organic matter, decrease soil erosion, withstand frequent mowing, give adequate grazing, reseeding, fast start, widely acclimated.

## G. Soybean (Glycine max)

► **Family:** Fabaceae

► **Type:** annual legume with edible seed

— The soybean is the world's most economically important bean, providing vegetable protein to millions of people as well as ingredients for hundreds of chemical goods

— N-fixing ability (kg/ha): 71–108

<figure><img src="image_10.png" /></figure>

## H. Pigeon pea (Cajanus cajan)

► **Family:** Fabaceae

► Pigeon pea is one of the most widely planted tropical and subtropical legumes for its tasty seeds. It grows quickly, is hardy, versatile, and drought resistant (Bekele-Tessema, 2007).

► Its drought resilience makes it extremely important for food security in locations where rainfall is unpredictable and droughts are likely to occur (Crop Trust, 2014). When other forages are scarce at the end of season, pigeon pea provides excellent green feed (Sloan et al., 2009).

► **N-fixing ability (kg/ha):** 120–170 (Adu-Gyamfi et al., 1997)

► **Benefits of pigeon pea:** large root system

enhances soil structure by shattering plough pans, increasing the soil's water retention capacity, its deep taproot may collect nutrients (such as P) from the soil's lower layers and deposit them in the upper layers, which is benefit other plants, immature stems and leaves act as green manure, fallen leaves act as a mulch, returning roughly 40 kg of nitrogen per hectare to the soil, add organic matter, erosion prevention and lowers soil temperature during heavy rains.

<figure><img src="image_11.png" /></figure>
## I. Cowpea (Vigna unguiculata)

* **N-fixing ability (kg/ha):** 14–35 (Okereke and Ayama, 1992)

— A versatile legume, having high in protein for human consumption and high in protein for livestock fodder. It enriches the soil by recycling nutrients through nitrogen fixation in collaboration with nodulating bacteria.

— Because of its adaptability to various types of soil and intercropping systems, drought resistance, and ability to improve soil fertility and prevent erosion, it is an important economic crop in many developing regions.

<figure><img src="image_12.png" /></figure>

## J. Rice bean (Vigna umbellata)

* **N-fixing ability (kg/ha):** 13–30

— Rice bean is a vibrant potential fodder legume crop which has capacity to provide balance diet to the livestock and to sustain under wide range of climatic condition. Appropriate focus on the crop is needed for more popularity as a potential legume crop under the climate change situation.

<figure><img src="image_13.png" /></figure>

## K. Mung bean (Vigna radiata)

* **N-fixing ability (kg/ha):** 19–54 (Hayat et al., 2008)

— Short-season crop that can tolerate dryland conditions and fix atmospheric nitrogen, reducing soil nutrient depletion.

— Serve as a multipurpose crop like harvest residues are used as fodder or green manure as well as a source of high-quality protein for human consumption.

<figure><img src="image_14.png" /></figure>
## L. Black gram (Vigna mungo)

* **N-fixing ability (kg/ha):** 16-79 (Hayat et al., 2008)

— The crop is resistant to harsh climatic conditions and improves soil fertility by absorbing atmospheric nitrogen. Protein, vitamin B, potassium, calcium, iron, niacin, thiamine, and riboflavin are all abundant in black gram. With 1.5 million tonnes of seeds produced annually, India is the world's largest producer of black gram, followed by Fiji, Mauritius, Africa, and Caribbean countries.

<figure><img src="image_15.png" /></figure>

— It is an important part of the Indian diet because it contains vegetable protein and serves as a supplement to a cereal-based diet. It contains approximately 26% protein, which is nearly three times that of cereals, as well as other minerals and vitamins. Furthermore, it is used as nutritive fodder, particularly for milch animals.

## M. Groundnut (Arachis Hypogaea)

* **N-fixing ability (kg/ha):** 150-200 (Toomsan et al., 1995)

* **Benefits:** increasing the organic matter, improving soil porosity, recycling nutrients, improving soil structure or tilth, decreasing soil pH, diversifying beneficial microorganisms, breaking up cycles of disease and pests

— Peanut cover crops are a win-win situation because they improve the soil while also providing a tasty, protein/nutrient-rich snack for the family

<figure><img src="image_16.png" /></figure>

## N. Chickpea (Cicer arietinum)

* Known as bengal gram, garbanzo bean, or Egyptian pea

* Its seeds are high in protein and one of the earliest cultivated legumes, under favorable conditions, the symbiotic N₂ fixation can

<figure><img src="image_17.png" /></figure>
produce as high as 176 kg N/ha and provide up to 85% of its N requirements in legumes.

► It is an important source of protein (16-20% in a vegetarian diet) and has become more important in addressing the problem of protein energy malnutrition (Prasad, 2012).

► It's also high in carbohydrates, fat, total dietary fiber, vitamins, and minerals (Hirdyani, 2014).

## O. Faba bean (Vicia faba)

► **Another name:** Broad bean, fava bean

- The broad bean is a hardy plant that can withstand harsh and cold climates. The broad bean, unlike most legumes, can be grown in both high salinity and clay soil.

- Fava beans present the highest protein-to-carbohydrate ratio among other popular pulse crops, such as chickpea, pea and lentil. Moreover, their

consumption is recommended along with cereals as both foods are complementary in supplying all essential amino acids

► **N-fixing ability (kg/ha):** 23-79 (Danso et al., 1987)

<figure><img src="image_18.png" /></figure>

## P. Lentil (Lens culinaris or Lens esculenta)

► **Benefits:** cover the threat of dry land agriculture, it can also be utilised to prevent soil erosion in problem regions.

- Mainly grown for its edible seeds

► **Type:** annual, bushy and herbaceous plant

► **N-fixing ability (kg ha⁻¹):** 8-14 (Cowell et al., 1989)

- Lentil can help agroecosystems that are short on water and nutrients produce more.

- Nitrogen fixation can provide up to 80% of the nitrogen requirements of lentils. The soil provides the remaining nitrogen (available at time of seeding plus mineralized during growing season).
### Q. Winged bean
(Psophocarpus tetragonolobus)

* **Family:** Fabaceae

* **Type:** An underutilized tropical herbaceous leguminous plant with high nutritional value,

* **Another name:** cigarillas, goa bean, fourangled bean, four-cornered bean, manila bean, princess bean, asparagus pea, dragon bean and 'soybean of the tropics' (Amoo et al., 2006)

- The immature pods contain 1% to 3% protein, as well as other nutrients; each of these parts contains vitamin A, vitamin C, calcium, and iron.

- Potential food source for ruminants, poultry, fish, and other livestock.

- Winged bean plant residues can provide enough N to the soil for the rice crop and provide an advantage equivalent to 4 to 8 g fertilizer N/m², respectively (Rahman et al., 2014)

<figure><img src="image_19.png" /></figure>

### R. Sword bean (Canavalia gladiata L.)

* **Type:** A tropical under-utilized food legume.

- It is rich in proteins and is cultivated as a vegetable and fodder crop.

- It has many desirable agronomic characteristics, such as high biomass production, resistance to drought, pests, and diseases, a high fertility index, and high seed productivity on fertile land, allowing it to grow well in tropical conditions.

- The presence of antinutritional compounds such as total free phenolics, tannins, Concanavalin A (Con A) lectin, L-Canavanine (a non-protein amino acid), phytic acid, oligosaccharides, protease inhibitors, and -amylase inhibitors prevent the seeds from being widely used as food/feed.

* **N-fixing ability (kg/ha):** 48.5 (Gargantini and Wutke, 1960)

<figure><img src="image_20.png" /></figure>
## S. Yam bean (Pachyrhizus erosus L.)

* **Family:** Leguminoceae is classified as a Fabaceae

— It is also known as "Potato bean" in English and "Mishrikand" in Hindi. It is known as 'Kesaru' in Bihar. In West Bengal, Assam, and Odisha, it is known as 'Sankalu' or 'Sankeshalu.'

— The yam bean, a close relative of the soybean and other beans, is grown for its large, tuberous roots. When mature, the pods are toxic, but when young, they can be eaten as a vegetable

— Because its tuber is nutritious and productive, yam bean cultivation is expected to lead to sustainable agriculture.

* **N-fixing ability (kg/ha):** 162-215 (Castellanos et al., 1996)

<figure><img src="image_21.png" /></figure>

## T. Hyacinth bean (Lablab purpureus)

* **Family:** Fabaceae

* **Common names:** lablab-bean, dolichos bean, seim or sem bean, lablab bean, Egyptian kidney bean, Indian bean, bataw and Australian pea

* **Type:** annual or short-lived perennial vines

— It is frequently grown as forage for livestock and as an ornamental plant due to the seed availability of one forage cultivar (cv. Rongai). Furthermore, it is mentioned as both a medicinal and a poisonous plant.

— The leaves can be eaten raw or cooked in the same way that spinach is, flowers are edible raw or steamed, for cooking, the root can be boiled or baked and Tofu and tempeh are made from the seeds.

<figure><img src="image_22.png" /></figure>

## U. Alfa alfa (Medicago sativa)

* **Family:** Fabaceae

* **Another name:** lucerne

* **Type:** Perennial forage and flowering plant

— It is grown in many countries as an important forage crop, used for grazing, hay, and silage, as well as a green manure and cover crop.

<figure><img src="image_23.png" /></figure>
- Alfalfa is a legume that can fix its own nitrogen (N) with the help of *Rhizobium meliloti*, a bacterium found in the roots of alfalfa plants. Nitrogen gas ($N_2$) in the air is converted by bacteria into a form that plants can use. A 5 ton/acre alfalfa crop can fix up to 250 pounds of nitrogen per acre per year (McKenzie *et al.*, 1999)

- Depending on subsoil constraints, the root system can grow to a depth of 2-3 m. Because of its deep root system, it improves soil nitrogen fertility and protects against soil erosion. Because of the depth of the root system and the perenniality of the crowns, which store carbohydrates as an energy reserve, it is very resilient, especially to droughts.

## V. Sesbania (Sesbania bispinosa), or (Sesbania aculeata) (wild.)

- **Another name:** dunchi, dhaincha, canicha, prickly sesban, jantar or spiny sesbania.

- An 8-week-old plant with both stem and root nodules fixed 1.50 mg nitrogen in a 12 h light period, but this decreased to 1.15 mg nitrogen after the stem nodules were removed, indicating that root nodules played a significant role in nitrogen fixation (Saraswati *et al.*, 1992)

<figure><img src="image_24.png" /></figure>

- **Uses:** industrial hemp for rope, fish nets, sackcloth and sailcloth. Its fibers are similar to those of birch trees and show promise as a source of paper fiber.

- The foliage makes a good fodder for livestock and the beans can be fed to fowl, its plant has been also used as a famine food by people, useful as a thickening agent, improve the soil via nitrogen fixation.

## 4. CONCLUSION

Grain/food legumes, as well as legume-inclusive production methods, can play an essential role in this setting by providing a variety of functions while adhering to sustainability standards. Indeed, legumes have critical roles at the food production, and cropping systems levels, as diversification crops in agroecosystems dependent on a few key species, interrupting pest and disease cycles, and helping to balance plant protein production deficits in many parts of the world. Legume crops having their own sustainable benefits to environment like-diversification, stabilization of plant-microbe metabolic cycles, erosion control, nutrient management, weed suppression, disruption of pest cycles, increased water infiltration and temperature stabilization.
Legumes offer a lot of potential for sustainable agriculture because they can be used as a growing crop or as crop leftover.

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