Nitrogen-Fixing Plants to Enrich your Soil

Alfalfa, Beans, Clover, Esparsette, Kudzu, Lespedeza, Peas, Peanuts, Soybeans, Winter Hairy Vetch

nitrogen-fixing plants, Alfalfa, Beans, Clover, Lespedeza, Peas, Peanuts, Soybeans, Winter Hairy Vetch

Nitrogen is among the top 3 vital nutrients for plants and crops, alongside potassium and phosphorus. It is responsible for chlorophyll and photosynthesis and is also a major component of amino acids.

What Is Nitrogen Fixation?

Though nitrogen makes up 80% of the volume of the atmosphere, it is unusable by most living organisms. It needs to be transformed into a digestible compound before it can be used.
Nitrogen-fixing plants are those with rhizobia bacteria that live on their roots and convert the atmospheric nitrogen into nitrogen compounds for their own use. Thanks to this relationship with this bacteria, these nitrogen-fixing plants increase the nutrients in the soil, making them also available to the plants nearby – a perfect relationship for companion planting.
Using nitrogen-fixing plants is a natural way to enrich your soil without using chemical fertilizers. A successful practice is to use nitrogen-fixing plants in intercropping. Heavy-feeding plants are intermixed with crops that add nitrogen to the soil. As an example, peas and beans benefit potatoes, carrots, cucumbers, cauliflower, cabbage, summer savory, turnips, radishes, corn, and most other herbs and vegetables.
Using nitrogen-fixing plants in crop rotation also allows nitrogen fixation for succeeding plants – because the nutrients are also available to plants grown in the soil after the nitrogen-fixing plants are pulled.
Legumes are known as the best nitrogen-fixing plants. These soil improvers collect nitrogen on their roots and restore it to the soil.
Some legumes are better at fixing nitrogen than others. The magnitude of biological nitrogen fixation and associated contribution varies across legume species, soil properties, climatic conditions, and cropping systems.
Perennial and forage legumes, such as alfalfa, clovers, and vetches, are the best crops for companion planting as they can fix substantial amounts of surplus nitrogen under the right conditions. However, they only add significant nitrogen for the following crop if the entire biomass (stems, leaves, roots) is incorporated into the soil. If a forage is cut and removed from the field, most of the nitrogen fixed by the forage is removed. Roots and crowns add little soil nitrogen compared with the aboveground biomass.
Grain legumes, such as peanuts, cowpeas, soybeans, and fava beans, are good nitrogen fixers as opposed to common beans.

Guide Information

Genus	Phaseolus, Lupinus

Nitrogen-Fixing Plants: Clover

Trifolium incarnatum (Crimson Clover)

Trifolium pratense (Red Clover)

Trifolium repens (White Clover)

Advantages Of Fixing Nitrogen With Cover Crop

A cover crop is a plant used to cover the soil rather than for the purpose of being harvested. It is mostly used to improve soil health, provide nutrients for other plants, slow erosion, smother weeds, attract beneficial insects and help control pests and diseases.

Try planting a cover crop of legumes. After flowering and before the seeds set, you can simply till under the plants. As these plants decay, they will raise the nitrogen in the soil without the need for commercial fertilizers. They will make nitrogen available to your lawn or plants that cannot get nitrogen from the air.

Best Cover Crop For Nitrogen Fixation

1. Alfalfa (Medicago sativa)
This is one of the most powerful nitrogen fixers of all legumes and may fix 250–500 lb of nitrogen per acre. Alfalfa is also strong in iron and is also a good source of phosphorus, potassium, magnesium, and trace minerals.

2. Clover (Trifolium):
Red Clover and White Clover can fix up to 150 lb of nitrogen per acre. They are used in spring or fall.

3. Peas or beans
They can be used as a summer nitrogen-fixing cover crop or harvested for food. Both ways, they enrich the soil with nitrogen.
Among them are Fava Beans, Green Beans or French Beans, Runner Beans, Soybeans, Chickpeas, Cowpeas or Black-Eyed Peas, Garden Peas, Field Peas, Lentils, Pigeon Peas, and Everlasting Sweet Pea.

While they all fix nitrogen, some are better at it than others. Fava beans top the list of nitrogen fixers, deriving 90% of their nitrogen from fixation. Peas and Lentils follow close behind at 80%, Chickpeas at 70%, and Soybean and dry beans at 50%

Nitrogen-Fixing Plants: Beans, Peas, Lentils and Peanuts

Arachis hypogaea – Peanuts

Cicer arietinum – Chickpeas

Glycine max – Soybeans

Lathyrus latifolius (Perennial Sweet Pea)

Lens culinaris – Lentils

Phaseolus coccineus – Runner Beans

Pisum sativum (Pea)

Vicia faba – Fava Beans

Vigna unguiculata subsp. unguiculata – Black-Eyed Peas

4. Vetches (Vicia):
Hairy Vetch, American Vetch, Wood Vetch, and Tufted Vetch. Vetches are winter-hardy and suitable for cooler seasons. Hairy vetch is the strongest type that is a good nitrogen-fixing winter cover crop. It is planted in early fall for the roots to establish before the first frosts.

5. lupins (Lupinus)

Lupins or bluebonnets are both an agricultural crop and an ornamental garden plant. They fix nitrogen, which benefits the soil, and act as green manure. As an added bonus, they add color and eye-catching beauty to any flower bed or garden spot. Native lupins also support wildlife by attracting native bees, bumblebees, and other pollinators.

Nitrogen-Fixing Plants: Lupin Flowers

Lupinus albifrons (Silver Lupine)

Lupinus arboreus (Tree Lupine)

Lupinus bicolor (Miniature Lupine)

Lupinus perennis (Wild Lupine)

Lupinus rivularis (Riverbank Lupine)

Lupinus texensis (Texas Bluebonnet)

6. Peanuts (Arachis hypogaea)
Peanuts are a legume with amazing nitrogen-fixing properties and are an excellent crop to plant in rotation with other crops.

By Koxae Sun, Shutterstock

While every effort has been made to describe these plants accurately, please keep in mind that height, bloom time, and color may differ in various climates. The description of these plants has been written based on numerous outside resources.