抄録
To establish an environment-friendly hydroponics system, the ion concentration control method for nutrient solution was developed.This demonstrated to be superior to the EC control method in respect to reduction of effluent and increase of yield. In this study, the technique for keeping a suitable pH value without using acid and/or alkali was examined; plants were cultivated under three concentrations of NH4-N. When the set point concentration of NH4-N was high, the pH value of nutrient solution fell rapidly after compensation of the component. However, when the set point of concentration of NH4-N was 5-8 mg l-1, the pH was rather stable. The pH value becomes stable when the ratio of NO3-N to NH4-N of nitrogen source is around 30 (total N: 120∼240 mg l-1). From the result of the comparative experiment on nutrient solution control methods on cucumber, it was suggested that new ideas on NH4-N supply should take into consideration of the ion concentration control method and that it includes not only set points of NH4-N concentration value but also the ratio of NH4-N to NO3 -N in the ion concentration.
