89 Nutrient Content in Rose Leaves as Affected by Potassium Applications through Drip Irrigation João Miranda dos Santos, José Geraldo Barbosa, Hermínia Emília Prieto Martinez, José Antonio Saraiva Grossi, Mariana Rubim, Thelma Mendes Pontes and Fernando Luiz Finger Plant Science Department, Federal University of Viçosa, 36570-000, Viçosa, MG, Brazil Keywords: Rosa, cultivar, leaf nutrient concentrations Abstract In order to evaluate rose leaf nutrient content as affected by potassium (K) dosages applied through drip irrigation, ‘Sônia’ and ‘Red Success’ cut roses were grown under a plastic greenhouse in Viçosa, Brazil. A randomized complete block split plot factorial experiment with four replications was carried out. The four potassium (K) dosages (0, 30, 60 and 90 g m -2 year -1 ) formed the main plots and the two rose cultivars the subplots. Foliar analysis was done in order to determine plant nutrient uptake curves during the plant growth and production cycles. In the absence of potassium (control), the leaf K contents decreased from 2.46 and 2.41 to 1.47 and 1.46 dag kg -1 after 60 and 635 days for ‘Red Success’ and ‘Sônia’ plants, respectively. With K application, leaf K contents decreased from 2.41 and 2.34 to 1.80 and 1.54 dag kg -1 after 60 and 635 days for ‘Red Success’ and ‘Sônia’, respectively, suggesting that the existing soil K was enough to provide satisfactory rose leaf K content, once the exhibited leaf K contents were in the optimal range for most commercial cut rose cultivars. INTRODUCTION Important aspects to optimize plant fertilization and nutritional plant status may be reflected by the adequate nutrient contents found in the leaves. Thus, foliar analysis must be regularly conducted, similarly to soil analysis. Optimum plant growth requires large K concentration in tissues, with critical nutrient levels being used to optimize adequate supply, maximizing the plant growth and development (Renner et al., 1995). Regarding rose plants, Almeida Neto (2001) reports that the highest rate of nutrient uptake by the roots is observed during the development of the floral stems increasing the ion storage capacity. Pizarro (1987) defines fertigation as the application of fertilizers dissolved in irrigation water, considering the existing compatibility between them. In order to use trickle fertigation by applying nutritive solutions in soil, soil and leaf analysis and the knowledge of the varieties behavior under such growing conditions are fundamental. According to Marschner (1995), potassium (K) is the most abundant cation in the cytoplasm and K salts play a major role in the regulation of the osmotic potential of the cells and tissues of most plants. Potassium plays a role in cellular extension and other regulatory processes of the cell turgescence, which are mainly related with its concen- tration in the cell vacuoles. Fertilizer recommendations for rose cultivation in greenhouse are not sufficient to make a precise and adequate inference, thus the determination of nutritional status of the plant is needed to allow an effective nutritional program. This work was undertaken in order to evaluate the nutritional levels in leaves of rose varieties cultivated under different doses of potassium, supplied by trickle fertigation. MATERIAL AND METHODS In this experiment ‘Red Success’ (red color) and ‘Sônia’ (pink rose) cultivars were planted three abreast at 30 cm spacings within rows (density of 10 plants/m 2 ). The experiment, done in a greenhouse at Federal University of Viçosa, MG, Brazil, was arranged in a random block design, with potassium application rates of 0, 30, 60 and 90 g/m 2 /year, applied in nutritive solutions (Table 1). The nutritive solutions were placed in Proc. IV th IS on Rose Research and Cultivation Ed. H.B. Pemberton Acta Hort. 751, ISHS 2007