Salinity is a serious threat to agriculture in arid and semiarid regions. Nearly 40% of the world’s land surface can be categorized as having potential salinity problems. Increases in the salinity of soils or water supplies used for irrigation result in decrease in productivity of most crop plants and lead to marked changes in the growth pattern of plants. Soil infertility in arid zones is often due to the presence of large quantities of salt, and the introduction of plants capable of surviving under these conditions (salt-tolerant plants) is worth investigating. Under agricultural condition, the amount of nitrogen removal is greater than the nitrogen input. To maintain soil fertility, nitrogen can be returned to the soil through biological nitrogen fixation (BNF) or by nitrogen fertilizer applications. To maintain soil fertility, nitrogen can be returned to the soil through biological nitrogen fixation (BNF) or by nitrogen fertilizer applications. Asymbiotic nitrogen-fixing bacteria, including the genus Azospirillum are considered to be among the most important micro-organisms that play a significant role in soil fertility in tropical and temperate regions of the world. The Rhizobium-legume symbiosis in arid ecosystems is particularly important for locations where the area of saline soils is increasing and becoming a threat to plant productivity. Legumes, which are usually present in arid ecosystems, may adapt to fix more N₂ under saline conditions than legumes grown in other habitats. It has been argued that P and K nutrition can enhance drought tolerance in plants. Application of mycorrhiza improves plant growth and nutrient acquisition and thus protects plants against salt stress in arid and semi-arid areas.  Therefore, the importance of inoculation of soil and plants with the beneficial microorganisms that enhance plant nutrition has been increased.