Legumes have a symbiotic relationship with rhizobia (root nodule bacteria). Rhizobia have the ability to fix atmospheric nitrogen which is unavailable for use by plants. Rhizobia transforms this atmospheric nitrogen (N2) into nitrates (NO3-), which then becomes available to the host plant, the legume. This process is known as nitrification and the rhizobia are nitrifying bacteria. In order to benefit from this naturally occurring symbiosis, the legume roots need to come in contact with the rhizobia bacteria. To attract the rhizobia to the roots, the legume root excretes a chemical to guide the bacteria to the root. Rhizobia populate the legume in small sacs in the roots, known as root nodules.

Although rhizobia exist naturally in most soil types, the quantity and availability for legume plants varies greatly, depending on the following factors: soil rhizobia availability, nitrogen availability, pH, temperature and moisture.

‘To ensure an optimum plant/nitrogen fixing relationship, legume seeds should be coated/inoculated with rhizobia. This will help to establish fertiliser factories within the root system of the legume plant.’