抄録
A technique for keeping a suitable pH value of nutrient solution without addition of acid and/or alkali examined. Cucumber plants were cultivated with various methods of NH4-N supply in ion concentration controlled hydroponic system.
In the first experiment, plants were grown in solution culture for 6 days at 4 levels of initial NH4-N concentration. NH4-N absorption rate increases drastically and solution pH decreased as the NH4-N concentration increased.
In the second experiment, cucumber were cultivated with nutrient solution controlled by the IIAS (Integrated IonAdjuster System) or the PEIS (Popular Edition of Intelligent System) to investigate the effects of NO3-N:NH4-N ratio, and concentrations of each N source on the growth and solution pH. Solution pH decreased severely under PEIS and IIAS (set value of NH4-N concentration 8 mg l-1), and increased under IIAS (NO3-N:NH4-N=30:1 or fuzzy) in this experiment. The results showed that pH of the nutrient solution for cucumber culture with IIAS management system could be stabilized by limiting NH4-N supply through the ratio basis control in which the ratio of NO3-N to NH4-N was kept at 30:1. However in the mid stage of cucumber growth with that system, the pH tended to increase gradually until harvesting stage, indicating that the relatively higher ratio of NH4-N supply in the mid stage than in other stages might be better to prevent the pH fluctuation.
To maintain pH value of the nutrient solution, the control method through the NO3-N:NH4N ratio was more feasible than the method through keeping the concentration of NH4-N.
