How could sea water be used to irrigate crops ?
Plant cells contain large amounts of dissolved compounds that lower the osmotic pressure of water within them. Water enters plant roots 2 because the osmotic pressure within root cells is lower than the matric potential 3 of water in soil pores. The plant wilts when the matric potential decreases to the point where capillary forces 5 holding water in soil pores equals the osmotic forces 1 that would draw water into plant roots. Usually the amount of salt dissolved in soil water is so low it can be ignored, but there enough dissolved salts in sea water lower its osmotic potential 1 making it difficult for plants to absorb water. Terrestrial plants are not adapted to overcome the low osmotic potential in sea water and, therefore, will wilt for lack of water if grown in sea water. That is why sea water is not used to irrigate 4 crops.
