As a control, a row of 29 boxes in a hydroponic system was installed, holding 1.2m3 LECA
(Fig. 2). Tap water was pumped from a separate 0.3m3 water reservoir at a rate of 5m3 h1, an fertilizer [19] was applied two or three times a week to maintain a fertilizer concentration with an electrical conductivity of 2.5mS cm1. This salt concentration was known to be the upper limit for vegetable growth from previous experiments at the institute [20–22]. Evaporated water was replaced continuously, holding the water
level constant. During tomato trials, a second control culture was planted in a natural, non-amended soil in the same greenhouse. Soil cultures were irrigated every few days with water from the fish tank, according to the irrigation need of the tomatoes (Fig. 2).