Effect of Phosphorus Application in Hydroponic Solution on Growth and Phosphorus Uptake in Chrysanthemum Plants

The relationship between phosphorus (P) uptake and growth rate of chrysanthemum plants grown hydroponically for cut flowers was investigated. In Exp. 1, fresh weight increase of chrysanthemum cv. Seiun plants at flower budding phase administered 0 to 40 ppm in culture solution for 16 days was evaluated. 1. P uptake by the chrysanthemum plants was nearly proportionate to P concentration in the culture solution. 2. The rate of increase in fresh weight of plants was not affected by the P concentration in the range of 20 to 40 ppm. In Exp. 2, to determine the optimum amount of P uptake for marketable cut flowers in chrysanthemum cv. Otomezakura, 50, 100 and 200 mg P per plant were applied at planting time. In another plot, 20 ppm P in culture solution was adjusted weekly by adding an equivalent amount of P absorbed by plants. 1. In the 50 mg P plot all P was absorbed by plants within 5 weeks after planting. The plants in this plot showed P deficiency symptom and delayed flowering. Although the phosphorus in the 100 mg P plot was wholly absorbed at within 7 weeks after planting (3 weeks before flowering), the plants grew and flowered normally. 2. Plants in both 200 mg P and 20 ppm P plots exhibited P excess symptom in the middle and lower leaves, e.g., chlorosis and pale green colour. 3. The rates of fresh weight increases in the four P plots were almost similar; their fresh weights were not significantly different at the end of the experiment. 4. The leaves of plants which absorbed up to 190 mg P and showed P excess symptom contained 0.51 to 0.70% P on dry weight basis, whereas leaves of plants which absorbed 50 mg P and showed P deficiency symptom contained 0.13 to 0.18% P.