Next - The ideal pH for water for irrigation is 5.5 to 7.0, whereas the pH in case of sea water ranges from 7.5 to 8.4. This makes it highly acidic, for a normal crop. Third, the density of the sea water ranges from about 1020 to 1029 kg/m3. read more
The salt in sea water would kill most of the plants that humans depend upon for food. In many places that get fresh water for irrigation eventually acquire such a buildup of minerals in the soil that they cannot be used for growing crops. There are plants-algae- that live in the sea but they have adapted to the salt over billions of years. read more