Influence of magnesium and salinity on tomato plants grown in hydroponic culture

Tomato plants (Lycopersicon esculentum, Mill) were grown in nutrient solution to observe the combined effect of three NaCl levels (1, 20, and 60 mM) and four magnesium (Mg) levels (0.5, 1.0, 5.0, and 10.0 mM) on fruit yield, water relations and mineral composition. Salinity at 20 and 60 mM NaCl reduced the marketable fruit yield compared to 1 mM NaCl. In non-saline conditions (1 mM NaCl), Mg concentrations of 1 mM or greater progressively reduced fruit yield, whereas in saline solutions (20 and 60 mM NaCl) fruit yield was depressed by Mg concentrations of 5 and 10 mM. The marketable fruit yield reduction was well correlated with salinity and Mg concentrations in the external medium (R-2=0.83). This harmful effect was related to the influence which NaCl and Mg had on plant water relationships and toxicity and/or imbalances in the mineral nutrition. In the conditions of this experiment, all components of the leaf water status were significantly altered and it was clear that calcium (Ca)-Mg and potassium (K)-sodium (Na) interactions took place. Therefore, the concentrations of Mg in the nutrient solution could be an important factor in the hydroponic culture of tomato grown under saline conditions.