directly under the plants. The sprayer was controlled by a cycling(2 min off and 2 s on) timer (Rhomberg Slimline ST-20, SouthAfrica). The air-supply was connected to the bottom of the reservoirto avoid sedimentation of nutrients by circulation and aeration. Thereservoir contained 30l of nutrient solution which was maintainedbelow the experiment. The aeroponic system was maintainedunder greenhouse conditions (60–70% relative humidity; 25 ± 2◦Cunder natural photoperiod conditions and a mid-day photosyn-thetic photon flux (PPF) of 950 ± 50 mol m−2s−1).