Abstract

Legumes are very important food sources and therefore, the nitrogen fixing ability of legume-rhizobia symbioses have great potential to improve crop yields. Biological nitrogen fixation, an important source of N in terrestrial ecosystems, plays a critical role in terrestrial nutrient cycling and net primary productivity. Symbiotic Nitrogen Fixation is the most effective and economic measures in agriculture to increase crop yield. Currently, symbiotic rhizobia refer to the soil bacteria in alpha and beta-proteobacteria that can induce root nodules on some legumes and a few of non-legumes. Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. This process is restricted mainly to legumes in agricultural systems, and there is considerable interest in exploring whether similar symbioses can be developed in non-legumes. A biotechnological approach where cereal crops are engineered to fix nitrogen has the potential to reduce fertilizer use in the developed world and greatly reduce the environmental impact. Nitrogen fixation in non-leguminous crops and bacterial associations has been investigated elaborately for their agronomic significance. Three approaches are currently considered as promising such as transfer of nitrogen fixation genes into organelles, root nodulation in cereals and endophytes. Different authors recognized that competent rhizobial strains could be applied to legumes and nonlegumes to increase their production. A number of abiotic factors affect symbiotic nitrogen fixation. The most important abiotic factors include water stress, temperature and soil acidity are influenced symbiotic nitrogen fixation. When studying any living organism, it is important to know how each species grows and responds to certain conditions that can be found in their natural environment. Future Prospects in biological nitrogen fixation has focus on efficient strain selection, inoculums production and quality. However, the nitrogen fixation research is the quest for nitrogen fixation in cereals.