0.3m3 water reservoir at a rate of 5m3 h_1, and
fertilizer [19] was applied two or three times a
week to maintain a fertilizer concentration with
an electrical conductivity of 2.5mS cm_1. 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).
2.2. Nutrient budgeting
As in the recirculation systems the complete
water volume passed over the trickling filter
once every 20min, concentration differences
between in- and outflow were within detection
0.3m3 water reservoir at a rate of 5m3 h_1, and
fertilizer [19] was applied two or three times a
week to maintain a fertilizer concentration with
an electrical conductivity of 2.5mS cm_1. 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).
2.2. Nutrient budgeting
As in the recirculation systems the complete
water volume passed over the trickling filter
once every 20min, concentration differences
between in- and outflow were within detection
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