Review on studies on the important role of symbiotic nitrogen fixation in agricu lture and livestock production and the factors affecting its efficiency

Symbiotic nitrogen fixation is the main part of BNF(biological nitrogen fixation) characterized by high efficiency and adopted in a wide range, and is of significant practicality as well. The amount of N₂ fixed by different legume crops from the atmosphere, the proportion of plant N derived from the N₂ fixation are introduced in this paper. And the N transferring from the legume to non-legume crops when they are intercropped, rotated or mixed with legume are discussed. At the same time, the main factors affecting the efficiency of symbiont between legume and Rhizobium are presented. The challenges that China is faced with are the increase of population, the decrease of land, resource decline and environmental deteriorate. To meet these challenges it is an effective way for sustainable agriculture to expand there search of symbiont between legume and Rhizobium.