Nitrogen Fixation in the Forest Garden

Many legumes have a symbiotic relationship with soil bacteria of the genus Rhizobium. These bacteria live in a plant’s roots, forming nodular swellings on the surface of the root. The nitrogen fixing process takes place in the nodules as the rhizobia absorb the nitrogen gas from the air and in the soil and transform it into useful compounds that plants can use. These compounds become available in the soil when roots from these plants decompose and when leaves from the plant drop onto and are incorporated into the soil. 

Nitrogen fixation is an important process and is better than the application of nitrogen fertilizer. Nitrogen fertilizer has to be used by plants immediately and the excess runs off into waterways. The process of nitrogen fixation makes nitrogen available to plants over the long run. The Forest Garden Approach uses nitrogen-fixing trees and vegetables in its design. Most but not all nitrogen fixing plants are in the legume family. Some common nitrogen fixing trees used in the FGA include: Acacia spp., Leucaena spp., and Calliandra calothyrsus. Other nitrogen fixing crops include beans, pigeon pea, and peanuts.