Legumes can supply their own nitrogen, provided that appropriate species of Rhizobium bacteria are present. This allows legumes to produce greater yields without additional nitrogen and also helps succeeding crops in the rotation.

Checking root nodules for nitrogen fixation is a straight forward process:

1.  Wait 4-6 weeks after planting. It takes this long for nodules to form and nitrogen fixation to begin.
2.  Dig out some of the root nodules attached to the roots.
3.  Slice the root nodules in half.
4. Check the colour of the interior of the root nodules. A pink colour means that nitrogen fixation is taking place.