Abstract
Tomato plants (Lycopersicon esculentum Mill., cv. House-Momotaro) were grown in a grower’s greenhouse (0.4 ha) using a commercial open rockwool system and a similar system equipped with a solution-recycling unit that we devised to reuse nutrient solution drained from the bed (closed rockwool system). In the closed system, the nutrient solution was prepared by adding tap water to drained nutrient solution collected in the mixing tank until the solution volume attained a given level, then concentrated fertilizer solutions were added until the EC of the solution reached a preset value. The elemental composition in the supply solution was adjusted at monthly intervals based on the chemical analysis of drained nutrient solution. Concentrations of nutient elements in the supply solution were not significantly different from those expected from its EC value and elemental concentrations in the fresh nutrient solution with the same EC value. The fruit yields of the two cultivation systems were not different. The closed system showed 22 to 47% reduction in the amount of nutrient elements applied and 33% reduction in the fertilizer cost compared with the open system. Thus, the closed rockwool cultivation system that we devised can be applicable to the large-scale commercial production of tomatoes. Problems to be resolved before this system is commercially introduced are discussed.
