Successful and profitable production of legumes requires nodulation by Rhizobium bacteria which supply the crop with fixed N. The appropriate strains of bacteria are often absent from soils, since they do not persist without a suitable host plant. Under these conditions, that is when the specific legume crop has not been planted in the field for more than 3 or 4 years, it is necessary to inoculate the seed (or sometimes the soil) with Rhizobium
