Limitation of high quality water resources and expansion of saline soils are the main challenges for agricultural development in many areas of the world, particularly in Iran . The increasing need for food production for the world growing population raised the importance of efficient management and application of marginal quality resources like saline waters. The salinity related researches, up to now, have been directed in two main aspects including increasing crop salt tolerance and introducing new management practices controlling the effects of salt stress on plants. On the other hand, different researches show the positive effects of root partial drought stress on regulating some mechanisms improving the plant water use efficiency. In this study the effect of equal and unequal distribution of salt in tomato root media on water use efficiency was investigated. The tomato seedlings were grown in a hydroponic system under four levels of equal and unequal salt distribution treatments. In equal salt distribution treatments, four salinity levels (i.e. 2, 5, 8 and 11 dS m -1 using NaCl) applied in nutrient solution. In unequal salt distribution treatments, the root was physically divided in two parts, where one was placed in nutrient solution and the other part in NaCl solution with 0, 3, 6 and 9 dS m -1 salinity levels. Then the root and shoot biomass and the plant water consumption were determined at the early flowering and fruit set stages. The plant nutrition status at flowering and some fruit quality parameters at maturity were also studied. In equal salt distribution treatments, the salinity decreased the root and shoot dry and fresh weight. With increase in salinity the plant water consumption was also decreased as such the consumed water per biomass remained unchanged for different salinity levels. Calcium, magnesium, and potassium concentration in the plant root and shoot decreased with salinity, while the sodium concentration increased sharply. On the other hand, salinity improved some quality attributes such as acidity, the dry matter weight, and the dissolved solids in the fruits. In unequal salt distribution treatments, at lower salinity levels (0 and 3 dS m -1 ), due to the reduced root growth and the absence of nutrient elements in NaCl solution, the plant biomass decreased; while, at higher salinity levels (6 and 9 dS m -1 ) despite the root growth impairment and reduced nutrient absorption, the plant biomass was similar to the control. Salinity, on the other hand, decreased the water consumption significantly that in turn caused Key Words: Salinity, Tomato, Hydroponics, Water Use Efficiency, Nutrient uptake.
