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The fertilizer nitrogen (N) inputs to some potted plants such as ornamental cabbage (Brassica oleracea L. var. acephala D.C.) are frequently higher than the actual demand. Optimization of N fertilization rate and selecting N-efficient cultivars are important approaches to increase the nitrogen use efficiency (NUE) and to reduce environmental pollution from nitrate leaching. The aim of this study was to assess the effect of increasing levels of nitrate (0.5, 2.5, 5, 10, or 20 mM of NO3 ) in the nutrient solution on plant growth, quality, soil plant analysis development (SPAD) index, chlorophyll fluorescence, leaf pigments, mineral composition, and NUE in five ornamental cabbage cultivars (Coral Prince, Coral Queen, Glamour Red, Northern Lights Red, and White Peacock), grown in closed subirrigation system. ‘Glamour Red’ and ‘Northern Lights Red’ needed 3.3 and 2.9 mM of NO3 L in the supplied nutrient solution, respectively, to produce 50% of predicted maximum shoot dry weight (SDW), whereas the vigorous cultivars Coral Prince, Coral Queen, and White Peacock needed 5.5, 4.7, and 4.3 mM of NO3 , respectively. Total leaf area (LA), SDW, SPAD index, N, Ca, and Mg concentrations increased linearly and quadratically in response to an increase of the nitrate concentration in the nutrient solution. Irrespective of cultivars, fertilizing above 10mMNO3 L produced high-quality plants (quality index of 5) and resulted in sufficiently high tissue concentrations of N, P, K, Ca, Mg, and Fe. Ornamental cabbage (Brassica oleracea L. var. acephala D.C.) is a common potted bedding plant all over the World. The ornamental cabbage aesthetic value in particular its attractive colored foliage, make it a very popular annual in the home landscape, especially in the fall and early winter seasons when other plants are senescing (Kushad et al., 2004). To produce high-quality ornamental plants, nutritional requirements especially Nmust be established. Nitrogen-nitrate (NO3 -N) is the main anion contributing to crop growth (Marschner, 2002), but also one of the major contributors to horticulturerelated pollution through leaching, particularly in areas where crops are grown in soilless culture with nonrecirculating nutrient solution (Rouphael et al., 2008; Rouphael and Colla, 2009). In fact, many ornamental crops grown in greenhouses are fertilized with an excess of N, since farmers are wary of reductions in N application that could result in any yield and quality losses (Glass, 2003; MacDonald et al., 2013). This practice would avoid any nitrate shortage, but would contribute to wasteful use of N fertilizer and increases in pollution of surface and groundwaters (Martinez et al., 2005). To face this challenge, ornamental industry is continually seeking to be environmentally friendly, whereas remaining competitive (MacDonald et al., 2013). Several strategies have been proposed to improve the NUE of crops including the selection of efficient cultivars (Rathke et al., 2006; Roberts, 2008). Optimization of N application rate is also crucial for commercial ornamental production. In fact, there is a critical N concentration below which the plants show a limited growth and above which the plant show a luxury consumption leading to environmental pollution and economic losses (Benincasa et al., 2011; Gamrod and Scoggins, 2006; Lemaire and Gastal, 1997). Moreover, different cultivars vary in their N demands, and consequently they perform best at different N concentrations (Marschner, 2002). For this reason, the identification of cultivars with high NUE could lead to low environmental impact on agrosystems while maintaining high crop performance (Hirsch and Sussman, 1999; Lynch, 1998; Sorgon a et al., 2006). Gourley et al. (1994) suggested that ‘‘a well-defined response curve is needed to determine differences in nutrient efficiency.’’ This approach allowed an estimation of the maximum yield/ growth (a) and the nutrient concentration necessary for half maximum yield/growth (b). Similar a and different b indicate efficient/inefficient cultivars, whereas different a indicates cultivars with lower/higher genetic potential (Gourley et al., 1994). These criteria has been successfully applied in herbaceous species in response to phosphate and potassium availability (Gerend as et al., 2008; Gourley et al., 1994), and also in the evaluation of the genotypic variation in Citrus, melon, and watermelon rootstocks at different nitrate levels (Colla et al., 2010, 2011; Sorgon a et al., 2006). Despite the importance of ornamental cabbage in floriculture production, few published data are available concerning N efficiency of ornamental cabbage cultivars (Gibson and Whipker, 2003). Gibson and Whipker (2003) studied the effect of N concentration in ornamental cabbage cv. Osaka white grown outdoors, and observed that fertilizing with 150 to 200 mg·L produced high-quality plants. However, the response of ornamental cabbage to N was only investigated on one cultivar and using three concentration levels, whereas information is lacking concerning the influence of different levels of N including ‘‘low-input’’ conditions on different cultivars, especially in soilless culture. The objective of this study was to assess the effect of increasing levels of nitrate in the nutrient solution on plant growth, quality, SPAD index, chlorophyll fluorescence, leaf pigments, mineral composition, and NUE in five ornamental cabbage cultivars (Coral Prince, Coral Queen, Glamour Red, Northern Lights Red, and White Peacock) grown in closed subirrigation system. Materials and Methods Plant materials, growth conditions, and experimental design. The experiment was Received for publication 23 Jan. 2015. Accepted for publication 24 Feb. 2015. We are grateful to Stefano Lazzaretti for the help in data collection. To whom reprint requests should be addressed; e-mail giucolla@unitus.it. 688 HORTSCIENCE VOL. 50(5) MAY 2015 carried out in Autumn 2012 growing season, in a 300 m polyethylene greenhouse situated on the experimental farm of Tuscia University, Central Italy (lat. 42 25#N, long. 12 08#E, alt. 310 m above sea level). Inside the greenhouse the daily temperatures were maintained between 12 and 25 C. Five ornamental cabbage (Brassica oleracea L. var. acephala D.C.) cultivars (Coral Prince, Coral Queen, Glamour Red, Northern Lights Red, and White Peacock), purchased from Nickys Nursery Ltd (CT10 2JU, United Kingdom), were transplanted on 19 Sept. into pots (diameter 16 cm, height 14 cm) containing 2.5 L of mixture peat:perlite in a 2:1 volume ratio. The pots were placed on 16-cm-wide and 6-m-long troughs, with 30 cm between pots and 25 cm between troughs, giving a plant density of 13.3 plants/m. Treatments were arranged in a completely random design with three replicates. Treatments were defined by a split-plot design of five nitrate levels in the nutrient solution (0.5, 2.5, 5, 10, or 20 mM of NO3 ) and five ornamental cabbage cultivars previously referenced, amounting to a total of 75 experimental unit plots. Each experimental unit consisted of six plants. Nitrate levels in the nutrient solution were assigned to main plots, whereas cultivars to subplots. Nutrient solution management. The composition of the nutrient solution used in the current experiment was: 1.0 mM P, 2.75 mM S, 4.0 mM K, 1.25 mM Mg, 20 mM Fe, 9 mM Mn, 0.3 mM Cu, 1.6 mM Zn, 20 mM B, and 0.3 mM Mo. Calcium nitrate was added to the nutrient solution to obtain the five nitrate levels (0.5, 2.5, 5, 10, or 20 mM) tested or the five ornamental cabbage cultivars. Furthermore, calcium sulfate was added to the nutrient solution to keep Ca concentration above 5 mM. The pH of the nutrient solution for all treatments was 6.0 ± 0.2. All nutrient solutions were prepared using deionized water. In all treatments nutrient solution was changed once a week to ensure sufficient nutrient for plant growth and to keep nitrate level in solution close to the targeted level. Nutrient solution was pumped from 15 independent tanks (one tank of 30 L per experimental unit) through a subirrigation system. In the subirrigation system the nutrient solution was pumped at the elevated end of the troughs and allowed to run slowly down the bench past the pots, and the excess was drained back to the tank for later recirculation. Irrigation scheduling was performed using electronic low-tension (LT) tensiometers (LT-Irrometer, Riverside, CA) that controlled irrigation based on substratematric potential (Norrie et al., 1994). Tensiometers have been placed at about the midpoint of the pots ( 7 cm depth) (Rouphael and Colla, 2005a, 2005b). In each treatment, three tensiometers were installed, and there were located in different pots to provide a representative reading of the moisture tension. Tensiometers were connected to an electronic programmer that controlled the beginning (–5 kPa) and end (–1 kPa) of irrigation, which correspond to the highand low-tension set points for the major part of the media (Rouphael et al., 2004). The timing varied from one to six fertigations per day lasting 20–30 min. Recording, sampling, and analysis. Eightytwo days after transplanting (12 Dec.), a chlorophyll meter (SPAD-502, Minolta corporation, Ltd., Osaka, Japan) was used to take readings from the fully expanded leaves. Twenty leaves per experimental unit were randomly measured and averaged to a single SPAD value for each treatment. On the same date, the chlorophyll fluorescence was recorded on 15 min dark-adapted leaves on six plants per experimental unit (five leaves per plant) by means of a chlorophyll fluorometer Handy PEA (Hansatech Instruments Ltd, King’s Lynn, UK) with an excitation source intensity higher than 3000 mmol·m·s at the sample surface. The minimal fluorescence intensity (F0) in a darkadapted state was measured in the presence of a background weak light signal ( 2–3 mmol photons·m·s). The maximal fluorescence level in the dark-adapted state (Fm) was induced by 0.8 s

Growth, Quality Index, and Mineral Composition of Five Ornamental Cabbage Cultivars Grown Under Different Nitrogen Fertilization Rates