A COMPARISON OF HYDROPONIC SYSTEMS FOR TOMATOES

1. Black plastic boxes each containing 6 to 7 litres of a nutrient solution.
2. Vertically hanging plastic bags with a fiber mat inside.
3. Rockwool slabs placed in double rows on plates of polystyrene and with continuous drip irrigation.
4. Rockwool slabs with intermittent drip irrigation.

The nutrient solutions were recirculated except for the latter system.

Rockwool slabs without recirculation gave the highest yield. The lower yields of the other 3 systems were due to one or more factors connected to the recirculated solutions: High nutrient concentrations induced when the plants were young and the light was limited in February and March; reduced oxygen concentration in periods with a high root activity; gradually increasing deficiency or excess of some of the nutrient elements, especially excess of Mn.

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