shows the setup of the floating bed system. Italian ryegrass seeds were sown onto expanded polystyrene boards (362 × 280 × 60 mm) and directly transferred into rectangular plastic tanks (380 × 285 × 145 mm) filled with 5 L of nutrient solution. Each board contained 20 plant pots. The bottom of the floating polystyrene board was covered with a 30 μm nylon membrane to prevent root pen- etration into the nutrient solution, i.e. allowing only a physical separa- tion from the solution below the board. Tanks were continuously aerated to avoid radical anoxia and to guarantee the constant mixing of the solution.