ABSTRACT
Forage legumes are now prominent components of pastures in many tropical and subtropical areas of the world. Their ability to associate with effective strains of Rhizobium bacteria is making an important contribution to sustainable agricultural systems. Through a symbiotic relationship, the bacteria supply nitrogen (N) directly to the legume and indirectly to adjacent grass plants, and add organic matter to the soil upon the decay of their nodules affixed to the roots of the legume. The information regarding nodulation and taxonomy of tropical rhizobia is still incomplete, but, when a new legume is introduced, inoculation with the appropriate Rhizobium will ensure that the legume will live up to its potential. There is a wide range of interactions between legume and bacterial strain, and effectiveness of the relationship depends on the specific forage legume’s Rhizobium requirement, which can vary from being very promiscuous to extremely specific. Acid soils of the tropics require symbiotic systems specially adapted to their conditions. It is now well established that tropical forage legumes can fix as much N as their temperate counterparts. The application of new biotechnology techniques to plants and associated microsymbionts will further increase forage yields and quality.
