The DFT hydroponic system was used in this study. The
plants were suspended on Styrofoam boards that floated on the surface of the nutrient solution (Fig. 4). The distance
between the plants was 10 cm. The nutrient solution had a
depth of about 15 cm and was circulated around the roots by
a pump and gravity drain. The average water temperature
was 26C. The nutrient powder (Accent hydroponics,
Thailand) was composed of 14.3% ammonium nitrate, 2.3%
potassium dihydrogen phosphate, 10.0% potassium nitrate,
2.8% potassium phosphate, 7.8% magnesium sulphate,
0.10% manganese sulphate, 0.006% copper sulphate,
0.005% zinc sulphate and 0.003% ammonium molybdate in
stock A and 8.6% calcium nitrate and 0.19% chelated iron
in stock B. Stock solution A was made by dissolving 20 kg
of stock A in 44 L of water. Likewise, stock solution B was
made by dissolving 20 kg of stock B in 44 L of water. Plant
standard nutrient was made by mixing stock solution A and
stock solution B in a 1:1 ratio and water was added to the
solution mixture to make a nutrient concentration of 21–
22 mS/cm, as determined by the conductivity factor (CF).
Plant standard nutrient with amino acid mixture was made
by adding 100 mL of amino acid mixture (Salute, Thailand)
to 10 L of stock solution B prior to combining with stock
solution A.