Nitrogen is the primary element responsible for vegetative growth in plants. It is the most abundant element in the Earth's atmosphere, but it has to be in a soluble form for plants to absorb and use it. One way that nitrogen is released into the soil is through the decomposition of organic matter. Another is the process of nitrogen fixation. In this process, specialized microbes colonize the roots of certain plants -- mainly from the legume, or bean, family -- and convert atmospheric nitrogen into a soluble form. Then the nitrogen is released into the soil when the roots of the plant die.
Select an appropriate legume species based on soil type, growing season and climate. Some legumes are better suited to sandy soils while others perform better in heavy clay. Warm season nitrogen-fixing crops are planted in spring after soil temperatures have reached 70 degrees. Cool season crops can be planted in either early spring or fall. Consult with your local Cooperative Extension Service office for advice on which nitrogen-fixing crops do best in your area.
Coat the seeds completely with the inoculant using nonchlorinated water. Be sure to the correct inoculant for the selected legume species. Seed suppliers usually sell the appropriate inoculant for each type of legume seed they offer, although preinoculated seed is available for some varieties.
Prepare the planting area by removing the existing vegetation and tilling to a depth of 4 to 6 inches. In smaller areas, a garden fork may be used to loosen the soil. Rake the soil into a smooth and even seedbed.
Broadcast seeds by hand or use a walk-behind spreader for large areas, evenly distributing them across the planting area. Rake the seeds into the soil with a hard metal rake to insure they are well covered. Place a light straw mulch over the planting area to discourage weed growth and water well to induce germination.
Cut the plants to the ground after they have matured with garden shears or an electric trimmer. To release the greatest amount of nitrogen to the soil, cut the plants when they are in full flower, but before any seed has formed. Till the remaining plant matter into the soil after it has been allowed to decompose on the surface for one to two weeks. The area can be planted immediately with another crop to make use of the available nitrogen.
Things You Will Need
- Garden tiller or digging fork
- Legume seed
- Legume inoculant
- Hard metal rake
- Garden shears or power hedge trimmer
- Soak seed in water for 24 hours before planting to speed up germination.
- Be aware that some nitrogen-fixing plants are invasive in some areas. Contact a local Cooperative Extension Service office for a list of invasive species in your area.
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