Yield and Quality of Tomato ( Solanum lycopersicum L.) Cultured in Bittern-Supplemented Hydroponic Solution

Abstract

Increasing the electric conductivity (EC) of the nutrient solution for growing hydroponic tomatoes (Solanum lycopersicum L.) is an effective way to increase fruit sugar content. The potential of bittern and coarse salt (NaCl) to cause high-EC stress, thereby improving fruit yield and quality in tomato plants under single-or double-truss cultivation were compared. Bittern is a by-product of the salt manufacturing process; it is easy to use and inexpensive. In particular, bittern is more convenient than common salt for high-EC treatment, because it is distributed as a solution, whereas common salt must be dissolved to very high concentration. The experiments reported herein were conducted during two growing seasons: spring and autumn. High-EC stress treatments (bittern or coarse salt) started when the largest fruit on the first truss was 4 cm in diameter. Fruit yield and Brix sugar content in the bittern treatment were similar or higher than in the salt treatment under both cultivation schemes. The EC of the bittern-added nutrient solution increased faster than that of the solution with added coarse salt. This trend was probably caused by the different ion compositions of bittern and coarse salt. There were no differences in tomato growth among treatments. Thus, bittern is a practical and effective additive for hydroponic single-truss tomato cultivation. thus, currently marketed tomatoes generally have high sugar content. Usually, the osmotic stress caused by increasing electrolyte concentration in the nutrient solution is effective for attaining the desired sugar content. Techniques developed to increase sugar content in hydroponic tomatoes include using highly concentrated nutrient solutions (Hohjo et al., 1996; Masuda et al., 1989), adding salt (NaCl) to the nutrient solution (Ohta et al., 1991; Oka et al., 2004; Tsunoda and Hayashi, 1988), or adding seawater to 1．Introduction Increasing sugar content in tomato (Solanum lycopersicum L.) fruit meets consumer demand;