The plants were grown in pots, 10.4 cm in diameter and 32 cm deep in which there were two layers of soil; 2200 g of air dry soil (subsoil) which contains the salt treatment and 800 g of untreated soil above (topsoil). Each layer was packed to a bulk density of 1.35 Mg m−3. The subsoil and topsoil were separated by a 3 cm layer of plastic beads 120 g. to prevent salt rising to the topsoil through capillarity action. The top 3 cm of the pot was also covered by plastic beads to minimize the water evaporation from the soil surface. A polypropylene tube (14 cm long, 2 cm internal diameter) was inserted into the upper 10 cm zone of each pot for watering the subsoil and referred to subsequently as a subsoil watering tube. During the first 3 weeks, plants were watered with reverse osmosis (RO) water from the top, but from 20 d after planting, watering was done only through the subsoil watering tube and the topsoil was allowed to dry. This watering method was used to simulate the topsoil drying that occurs in the field.