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This experiment was conducted to examine the effects of mixing ratio of perlite and coir dust on the growth and development of hydroponically grown chrysanthemum (Dendranthema grandiflorum cv. Backwang). Perlite and coir dust (the short fibers and dust from the mesocarp of coconuts, Cocos nucifera) were mixed interproportionally as of 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100 (v/v). Number of leaves increased in the mixing ratio of 40 percent perlite and 60 percent of coir dust and then followed by the mixing ratio of 20 percent of perlite and 80 percent of coin dust, and leaf area increased in the mixing ratio of 20 percent of perlite and 80 percent of coir dust as of 2317 ㎠. In the treatments with higher content of coir dust, the fresh and dry weight of leaf and stem increased. Especially, in the treatments with higher content of perlite, dry matter was much more partitioned to the flower. N03=N uptake of chrysanthemum increased during the early and middle stage of growth and then decreased with increasing amount of NO₃^--N content in drained solution. Especially, NO₃^--N content in drained solution was higher as mixing ratio of perlite increased. K^+ content in drained solution was maintained constantly until solution exchange in all treatment, but afterward K^+ content sharply decreased with H₂PO₄^-. Depending on the mixing ratio of perlite and coir dust, the uptake of NH₄-N was changed. NH₄-N was not drained in the plot of mixing ratio of 80 and 100 percent of coir dust, but in the plot of mixing ratio of 80 percent of perlite, NH₄-N content in drained solution increased. These results demonstrated that mixing ratio of perlite and coir dust significantly could change the uptake of NH₄-N in hydroponically grown plants.
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