Nitrogen Fixation in the Forest Garden:

Modern farming generally relies on the application of nitrogen fertilizer, which must be used by plants shortly after application before it leaches into groundwater. Nitrogen fixation is an important natural process that benefits farmers far more than synthetic fertilizers, as it’s climate-smart, low-cost, and can be utilized by plants for longer periods.

Most nitrogen fixing plants are in the legume family, such as beans and pigeon pea. 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 roots. The nitrogen fixing process takes place in the nodules as the rhizobia absorbs the nitrogen gas from the air and in the soil and transforms 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.  

Not all nitrogen fixing plants are legumes. The Forest Garden Approach incorporates nitrogen-fixing trees and other plants in its design, such as Acacia spp., Leucaena spp., and Calliandra calothyrsus. These trees are most often incorporated in alleys and living fences to support neighboring crops.