Effects of silicon and salinity on fruit yield and quality of tomato grown hydroponically

The effects of silicon added to the nutrient solution either at a standard electrical conductivity (EC) of 2.2 dS m sup -1 or at an increased EC of 4.8 dS m sup -1 on yield, nutritional status and fruit quality were investigated in a tomato crop grown in a closed hydroponic system. Si was added in form of a water-soluble potassium silicate compound at a reference concentration of 2.25 mM. The EC was raised either by NaCl of by extra addition of K, Ca, and Mg salts of nitrates and sulfates at rates resulting in the same K:Ca:Mg and NO3:SO4 ratios and NH4, P, and micronutrient concentrations in all treatments. The average EC values in the drainage water were 3.7 and 3.4 dS m sup -1 in the low EC treatments without and with Si supply, respectively, and 5.8, 5.7 and 5.8 dS m sup -1 in the salinity treatments involving NaCl addition, NaCl and Si addition, and extra nutrients combined with Si addition, respectively. The increase of EC up to 4.8 dS m sup -1 by adding NaCl had no significant influence on the fruit yield of tomato, when Si was added to the saline nutrient solution. In contrast, the fruit yield per plant was significantly restricted at this level of salinity, when no Si was added to the NaCl-enriched nutrient solution, or when Si was included but salinity was induced by extra addition of major nutrients. In both cases, the yield depressions were exclusively due to a lower mean fruit wight. The b-carotene and lycopene contents of fruit were significantly increased by Si and nutrient-induced salinity. Both Si and EC enhanced the fruit firmness and the contents of total solid solutes and vitamin C in the tomato fruit. Moreover, the addition of Si significantly restricted the occurence of blossom-end rot in tomato fruit when the plants were not exposed to salinity.