Nutrient Uptake of Single-stemmed Roses under Macro- and Micro-element Amendment in a Closed Aeroponic System

A considerable imbalance of minerals in a hydroponic nutrient solution is often found when plants are grown in a recirculating (closed) system. The aim of this study was to determine a proper method to amend the nutrient solution in the recirculating system in order to maintain a balanced mineral status in the root zone and thus improve the quality and productivity of two single-stemmed roses (Rosa hybrida L. 'Vital' and 'Red Velvet') grown for seven weeks in a closed aeroponic system. Mineral ions in the closed aeroponic system were adjusted by changing electrical conductivity (EC treatment), concentrations of N, P and K (NPK treatment), macro-elements (M treatment), and macro- and micro-elements (MM treatment), and by supplementing a nutrient solution of 1.5 dSㆍm-¹ (S treatment). For two weeks after transplanting, the pH level significantly decreased in the solution under the EC and S treatments for both cultivars with a higher degree in 'Red Velvet'. It was coincidently observed that NH₄-N and P concentrations were lower under the EC and S treatments than those under the other treatments. The EC level and NO₃-N and K concentrations were the highest under the S treatment for both cultivars from 5 weeks after transplanting. In contrast, the EC level greatly decreased under the NPK treatment more than under the other treatments, coinciding with lower concentrations of Ca and Mg. The pH, EC and mineral nutrient status were more stable in the M and MM treatments compared to the other treatments. The greatest supply and absorption of water was observed in the EC treatment. While there was no difference in the water supply and absorption among the S treatments and the NPK, M and MM treatments, the largest amounts of NO₃-N and K and the smallest amounts of NH₄-N and P were supplied to both cultivars under the S treatment. The smallest amount of fertilizer was used in the EC treatment, whereas the largest amount was used in the S treatment. Average usage of fertilizer was decreased by 17% for both cultivars under the M and MM treatments compared to the S treatment.