Effect of salinity application on yield and quality in the hydroponically grown baby-leaf vegetables

The demands of baby-leaf vegetables have been increasing all over the world. In general, quality of baby-leaf vegetables decreases in hot season production and the establishment of stable production system with high quality has been desired. The effects of salinity application to 3 Amaranthaceae, 9 Asteraceae and 10 Brassicaceae crops were examined for improvement of the yield and quality. Baby-leaf crops were sown into styrofoam trays containing peat-based medium, and were transferred to the floating growing system (FGS) after thinning out to ca. 1,500 plants m-2. Four salinity treatments were carried out by adding NaCl into the nutrient solution: 1) 2.5 dS m-1 for about two weeks from starting of FGS to harvest (control); 2) 5.0 dS m-1 for about two weeks from starting of FGS to harvest; 3) increasing from 2.5 to 5.0 dS m-1 for about one week before harvest; and 4) increasing from 2.5 to 7.5 dS m-1 for about one week before harvest. The longer period and the higher EC level of the salinity treatment was carried out, the more Na+ all the crops absorbed. The sum of Na+, K+ and Ca2+ contents by two-week salinity treatment before harvest was lower than those by one-week treatment in most of the Brassicaceae crops. The yield increased due to rise of water content by the salinity treatment in table beet. The ascorbic acid contents increased due to increasing the Na+ absorption in spinach. The total phenolics contents increased due to the rise of three-cations contents in ‘Green Romaine’ lettuce and rucola. The nitrate contents tended to decrease by the salinity treatment, according to the increasing Na+ contents especially in Asteraceae crops.