water desalination for agriculture, necessity, importance and limitations

today, shortage of fresh water especially in arid and semi-arid regions has caused several difficulties.  whatever more than 70 percent of the earth is water, but also high salinity of water resources, caused serious restrictions for human to use these resources. therefore, desalination has attracted all attentions more than any time. between different water consumers in the country, agriculture with consumption of more than 90 percent of the country water recourses has devoted the highest portion, but unfortunately, in the most part of the country, shortage of fresh water resources for agriculture  feel, yet. so, in this article, attempted to explain different desalination methods in the world, briefly and finally, necessity, importance and application restrictions of these methods in the country, is investigated.