Effects of Nitrogen Concentration and NO₃-:NH₄+ Ratio of Nutrient Solution on Stock Plant Growth, Cutting Yield, and Quality in Kalanchoe blossfeldiana

To determine the optimum N concentration and NO₃-:NH₄+ ratio of nutrient solution for stock plant growth and cuttings production, Kalanchoe blossfeldiana 'Margrethe' plants were applied with nutrient solutions containing N at 6, 12, and 24 mM (6 N, 12 N, and 24 N) and NO₃-:NH₄+ ratio (in mM) of 24:0, 20:4, 16:8, and 12:12 from 6 to 14 weeks after planting. High N promoted stock plant growth by increases in photosynthetic rate, stomatal conductance, and transpiration. High N application also increased chlorophyll and soluble protein contents and accumulated more assimilates in cuttings. High N application to stock plant increased the contents of not only N but also other macroelements except K in cuttings. Especially, the 24 N treatment increased the uptake of B, an important element for adventitious rooting. Cuttings from higher N-applied stock plant rooted more rapidly and had better growth at 3 weeks after cultivation. In NO₃-:NH₄+ ratio experiment, stock plant growth was stimulated with increasing NH₄+ ratio. The ratio of NO₃- to NH₄+ of 16:8 significantly increased number of cuttings, leaf area, and fresh and dry weights. NO₃- and NH₄+ contents increased with increasing NO₃- and NH₄+ ratio, respectively. The content of P was lowest at the ratio of NO₃- to NH₄+ of 24:0. However, cation contents in cuttings were higher with increasing NO₃- ratio. Higher NH₄+, at the ratios of NO₃- to NH₄+ of 16:8 and 12:12, significantly increased total nonstructural carbohydrates and starch contents of cuttings. Total soluble protein and chlorophyll contents were higher at the ratio of NO₃- to NH₄+ of 16:8 than at the ratio NO₃- to NH₄+ of 24:0. After 21 days of cultivation, medium NO₃-:NH₄+ ratios, 16:8 and 20:4, positively affected rooting and growth of cuttings, increasing leaf area, root fresh and dry weights, and shoot fresh and dry weights of cuttings. Whereas, top/root ratio was smallest at the ratios of NO₃- to NH₄+ of 20:4 and 16:8 meaning that root growth was relatively better than shoot growth. However, the highest NH₄+ ratio, 12:12, negatively affected root growth of cuttings, although it somewhat promoted stock plant growth. In conclusion, we recommend to maintain N concentration at 24 mM with 16 mM NO₃- and 8 mM NH₄+ for stock plant growth and cutting production in K. blossfeldiana 'Margrethe'.