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What are Legumes?

'Legumes' belong to a family of plants which we often refer to as 'peas' and 'beans'. They are grown as a food crop, mainly for their grain seed called pulse. They are regularly consumed in many households, and some of the most familiar members include soybeans, peanuts and lentils.

Apart from their economic and nutritional values, legumes have a unique ability that distinguishes them from all other plants. They are capable of forming beneficial partnerships with a special group of soil bacteria known as 'rhizobia'.This collaboration between plant and bacteria makes it possible for legumes to harvest nitrogen from the air and convert it into forms usable for their growth and productivity.


What are Rhizobia?

'Rhizobia' is a collective name given to groups of soil bacteria that can form a symbiotic partnership with legume roots. A rhizobial species that is compatible with a particular legume plant can infect its roots and form globular/spherical structures on the roots termed 'nodules'.

Within these nodules, a chemical reaction takes place that allows atmospheric nitrogen to be converted into plant nutrients. Rhizobia therefore play a significant role in promoting and improving soil fertility and productivity.


Nitrogen Fixation

The benefit of this 'nitrogen fixation' is not limited to the legume plant alone. Once the plant decomposes, nitrogen is returned to the soil, which is then available to every other plant in the vicinity. In other words, legumes can contribute additional external nitrogen to the crop-soil ecosystem.

Although legumes have long been used in agriculture, their natural process for harvesting nitrogen has largely been replaced with the application of synthetic nitrogen fertilisers that were first introduced around 200 years ago, during the agricultural revolution.

Nitrogen Fixation Drawing

© Kasper De Bruyne