THE RELATIONSHIP BETWEEN GROWTH OF A ROSE PLANT AND ITS NUTRIENT AND WATER-UPTAKE IN HYDROPONIC CULTURE

To develop a new method of fertigation in cut flower production of ros es, the relationships between plant growth and its nutrient and water uptake and tie ratio of cut flower to plant growth were investigated. Two-year-old rose plants, cv. Sonia and Carl Red, grafted on Rose mult iflora Thunb. were grown hydroponically for about a year. The overall plant growth was determined by weighing separately cut flowers, prunin gs, defoliated leaves, roots, trunks, and old leaves. The growth rate decreased immediately after harvesting cut flowers and pruning. On a l ong term basis, however, the growth rate was slower in summer than in other seasons. Growth in 'Sonia' plants was faster than that in 'Carl Red' plants. After flower production had become stable, the ratio of c ut flowers to plant growth on a fresh weight (FW) basis was always abo ut 40% in both cultivars. The amounts of nutrients absorbed per 100 g increments of plant FW in both cultivars were about N: 0.70 g, P: 0.10 g, K: 0.40 g, Ca: 0.17 g, and Mg: 0.04 g. The amount of nutrients abs orbed per 100 g cut flowers were 2.5 times greater than those on per p lant FW basis. ' Sonia' plants absorbed 2-3 liters of water in winter, 4-5 liters in spring and fall, and 8-9 liters in summer per 100 g FW. 'Carl Red' plants absorbed more water than 'Sonia' plants. The concen tration of nutrient absorbed by the plant (nutrient/water) was lower i n summer than in winter, and that of 'Carl Red' was nearly 80% of 'Son ia'. The amount of nitrogen absorbed by 'Sonia' plant was about 230 pp m in winter, 145 ppm in spring and fall, and 110 ppm in summer. The am ounts of P, K, Ca, and Mg uptake by plants were on the average 14, 60, 24, and 6 percent of N, respectively.