Kyung-Hwan Yeo

Determination of optimal levels of Ca and Mg for single-stemmed roses grown in closed aeroponic system

In the production of single-stemmed roses in a closed system, it is necessary to identify the optimal ranges of ions in the nutrient solution in order to determine the optimal management practices for the crop. This study was conducted to determine the optimal levels of Ca2+ and Mg2+ in the nutrient solution for optimization of nutrition of single-stemmed roses grown in a closed aeroponic system. Single-stemmed roses were grown in the nutrient solution with 7 different levels each of Ca (0, 10, 40, 80, 120, 160, and 200 mg·L−1) and Mg (0, 10, 20, 40, 80, 120, and 160 mg·L−1) for four weeks after transplanting. A sharp pH change was observed in the treatments with low levels of Ca2+ and Mg2+ during the first and second weeks after transplanting, and there was a stable variation in EC in a range of 1.3–1.8 dS·m−1 in the treatments of 40–120 mg·L−1 Ca and 10–80 mg·L−1 Mg. Contents of Ca and K contents in leaf tissue were significantly decreased by increasing Mg2+ level in the nutrient solution. Although there was an increase in the fresh weight and stem length under higher levels of Ca2+ and Mg2+, plant growth did not increase as compared to the treatments of 120 mg·L−1 Ca and 80 mg·L−1 Mg. Photosynthetic rate in the leaves of flowering shoots was the greatest in the range of 80–120 mg·L−1 Ca, and the stomatal conductance and transpiration rate had a tendency to increase along with the increase of Ca2+ concentration up to 120 mg·L−1 before distinct decrease at Ca2+ level greater than 160 mg·L−1. In Mg treatments, photosynthetic responses showed maximum values at around 40–80 mg·L−1, and began to decrease at level greater than 80 mg·L−1. Photosynthetic water use efficiency (WUE) was lower in leaves of the treatments of 160 and 200 mg·L−1 Ca, and 0 and 160 mg·L−1 Mg. Chlorophyll content in five-leaflet leaves as influenced by Mg2+ level tended to increase continuously up to 80 mg·L−1, showing a positive correlation with Mg content in the leaves. Content of anthocyanin in five-leaflet leaves was higher in the treatments with low Mg2+ levels (0 and 10 mg·L−1). Considering the nutrient and water absorption patterns, and growth characteristics of single-stemmed roses with different solution Ca2+ and Mg2+ levels, 80–120 mg·L−1 Ca and 30–80 mg·L−1 Mg seem to be appropriate for the optimization of plant nutrition in a closed production system.

Effects of Light Intensity, Nutrient Solution Compositions before Harvest and the Time of Nutrient Solution Removal on Nitrate Contents in Hydroponically-Grown Leaf Lettuces in Closed Plant Production System

The nitrate (NO3 ) accumulation of hydroponically grown leafy vegetables may increase in the condition of a closed-type plant production system with low light intensity due to low activity of enzymes involved in nitrogen assimilation and the use of NO3-N as major nitrogen source. The objective of this study is to investigate the effects of light intensities, nutrient solution compositions and the time of nutrient solution removal before harvest on nitrate contents of hydroponically-grown lettuces in a closed plant production system. The reduction of nitrate contents in leafy lettuces ‘Cheongchima’ was higher in the treatments of ‘TW’ (nutrient solution removal) and ‘(NH4)2CO3’ (use of ammonium carbonate as nitrogen source) than those in other treatments, which significantly lowered fresh weight and leaf area of the plants. In the light intensity of 100 μmol·m·s, the nitrate content was effectively reduced without causing any growth retardation, by substitution of the nutrient solution composition that NO3-N was removed (‘NO3-N removal’ treatment) or the half strength of standard nutrient solution was applied (‘1/2 S’ treatment), for 7days before harvest. The effects of light intensity and the time of nutrient solution removal before harvest on growth and nitrate contents in leafy lettuces were investigated. The nitrate contents in leaves under the light condition of 300 μmol·m·s before nutrient solution removal were lower than those of 100 or 200 μmol·m·s. The removal of nutrient solution for 7 days before harvest quickly reduced the amount of nitrates in leaves in all the light intensities with a greater degree under the 300 μmol·m·s of light condition, while the 7 days-removal with both 200 and 300 μmol·m·s of light conditions caused decrease in 16~31% of leaf area and 20~35% of fresh weight, compared to the 3 days-removal treatment. The nitrate contents were greatly reduced from 3,018 to 1,035 in 200 μmol·m·s, and 2,021 to 480 ppm in the light condition of 300 μmol·m·s, with the nutrient solution removal for 3 days before harvest, without causing any deterioration in growth and product quality. The vitamin C contents in leaves were higher in the treatment of nutrient solution removal for both 3 and 5 days before harvest with the light condition of 300 μmol·m·s than those in the light condition of 100 or 200 μmol·m·s. Additional key words : ammonium carbonate, NO3-N removal, vitamin C, growth characteristics

Erratum to: Optimal levels of N, P, and K for the cultivation of single-stemmed roses in a closed hydroponic system

It is necessary to identify the optimum levels of mineral nutrients for the commercial production of single-stemmed roses in a closed hydroponic system to avoid the accumulation of undesirable ions in the root zone and to improve shoot growth and flower quality. We determined the optimal concentrations of nitrogen (N), phosphorous (P), and potassium (K) in a nutrient solution by analyzing the amount of mineral nutrients absorbed by the plant, plant growth, and photosynthesis characteristics. Rose plants (Rosa hybrid L. cv. Red Velvet) were subjected to different concentrations of macronutrients, including N (0, 10, 50, 100, 150, or 200 mg·L-1), P (0, 10, 20, 40, 80, or 100 mg·L-1), and K (0, 10, 50, 100, 150, 200, or 250 mg·L-1). The uptake of nitrate-N (NO3-) was inhibited by high P levels, and the NO3-N concentration in the nutrient solution was significantly higher in the 100 mg·L-1 P treatment than in the other P treatments, indicating reduced NO3- uptake by the plants. The concentration of phosphate (PO4-) decreased considerably in all N and K treatments during the entire growth period. To ensure a sufficient supply of P for single-stemmed roses, it is necessary to increase the PO4- concentration in the nutrient solution. Increasing the K+ level significantly increased the concentrations of calcium (Ca2+) and magnesium (Mg2+) in the nutrient solution. This may be the result of low Ca and Mg absorption from plants over the growth period. Although there was an increase in the fresh weight and stem length with higher levels of N [NO3- and ammonium (NH4+)], PO4-, and K+, growth did not significantly increase at levels higher than 150 mg·L-1 N, 40 mg·L-1 P, and 200 mg·L-1 K treatments. The photosynthetic rates (Pn) increased rapidly as the concentration in the nutrient solution increased to 100 mg·L-1 N, 40 mg·L-1 P, and 150 mg·L-1 K, followed by a reduction as the ion concentrations increased to the maximum ranges. A distinct reduction of the Pn was observed in the plants supplied with nutrient levels above 150 mg·L-1 N, 80 mg·L-1 P, and 200 mg·L-1 K. Considering the nutrient-water absorption patterns, growth, and photosynthesis characteristics of single-stemmed roses, the mineral nutrient levels of 100–150 mg·L-1 N, 30-50 mg·L-1 P, and 100–150 mg·L-1 K were found to be optimal for the production of single-stemmed roses in a closed hydroponic system.