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Potted gerberas were grown in a greenhouse with one, two, or four emitters (1.2 L·h) per pot and irrigated with water of two levels of salinity (1.5 dS·m and 3 dS·m). All pots received the same volume of water. The aim was to determine whether the number of emitters per pot affects the distribution of roots and salts in the substrate (100% coconut fiber). We determined the electrical conductivity (EC) distribution at three different heights (upper, middle, and lower). We also studied the roots and EC horizontal distribution in four quadrants (southeast, southwest, northwest, and northeast). Shoot growth, leaf damage, plant water status, and photochemical capacity of photosystem II were also studied. Two or four emitters per pot reduced the leaching fraction compared with that observed with one emitter, improving both the amount and homogeneity of substrate moisture. In the two saline conditions used, the salt concentration in the substrate was irregular both vertically and horizontally, and the presence of roots in the horizontal quadrant sides was heterogeneous. Both of these behaviors decreased as the number of emitters per pot increased. Root growth was weakly related with the soluble salt content in the root zone. When saline water is used, two emitters per pot are to be recommended because the difference between using two and four emitters was very slight. The use of only one emitter reduced shoot and root growth and encouraged salt damage to leaves. Irrigating with saline water leads to the accumulation of salt in the root zone, which reduces plant size and growth, alters plant development, and causes leaf damage. These effects are more pronounced in containergrown crops, in which the growing medium is more limited than in the ground, and, as a result, the aesthetic value of ornamental plants is reduced. Over the last 25 years, numerous studies have been conducted to improve the irrigation of potted plants. Many of these studies have focused on the effects of different irrigation methods and systems on the accumulation and distribution of salts and roots in the more common substrates, taking into consideration different fertilizer sources and rates (Argo and Biernbaum, 1994, 1995; Morvant et al., 1997). Progress has also been made in scheduling irrigation (Million et al., 2007); however, few studies have compared different ways of applying water over the surface of the substrate. Drip irrigation is generally thought to be a very efficient irrigation technique (Wang et al., 2011) and is the most widely used method for potted plant production. The basic concept underlying drip irrigation is to keep a bulb of soil moist so that roots can absorb water. The volume and shape of the wet bulb irrigated by each emitter are a function of the characteristics of the substrate (texture and hydraulic conductivity) and the discharge rate of the emitter (Awulachew et al., 2009). However, the number of water emission points over the substrate surface may also have an influence. Drip irrigation usually uses one emitter per pot for small containers, and very few published papers have studied the effect on growth and variations of roots and salts in the root ball when two or more emitters per pot are used. Ondrasek et al. (2008) reported the position of the emitters in the pot could strongly affect the moisture and salt distribution in the substrate. Our hypothesis was that applying the same volume of water to pots using more than one emitter may influence the retention and diffusion of moisture in the substrate and, as a consequence, the distribution of salts and roots. To verify this, coconut fiber-grown gerbera were irrigated with one, two, and four emitters per pot under two levels of salinity (control or saline irrigation) during a spring–summer growing season determining the effects on substrate and leachate EC, root growth, shoot growth, leaf damage, plant physiological status, and leaching fraction. Materials and Methods Plant material and growing conditions. Seedlings of Gerbera hybrid cv. Triana were transplanted into 3.75-L pots (20-cm upper internal diameter and height 18 cm) containing 100% coconut fiber substrate (Projar Professional Cocopeat; Projar, S.A. Valencia, Spain). The substrate fill height was 16 cm. The experiment took place in a greenhouse with a semicircular cover (12 m length · 7 m width, 3 m height at the side, and 4.5 m at the center) located at the Agricultural Experimental Station of the Polytechnic University of Cartagena (Cartagena, Spain). The top part was covered with polyethylene (PE) film and green shading screen (50% shade). The sides were covered with PE film and antiaphid mesh; the PE film could be rolled up for ventilation. The front and the back were covered with antiaphid mesh. The pots were introduced into white pots (f 24 cm) kept in place in holes (21 cm · 21 cm) in a metal grid made of corrugated bars (8 mm diameter), 80 cm off the ground. This experiment was conducted from the first week of Mar. 2012 to the second week of Sept. 2012. The irrigation system used pressurecompensating and antidrain emitters, which emit 1.2 L of solution per hour (Netafim Ltd. Corporate Headquarters, Tel Aviv, Israel). The emitters used were tested for homogeneity before the experiment started (the water flow varied between 1.16 and 1.24 L·h). The emitters were attached to a tube (60 cm · 4 mm) and were inserted into the substrate by means of a plastic straight arrow. The irrigation system was controlled by a system similar to that described by Nemali and van Iersel (2006) but using a CR1000 data logger, which controlled the water pumps through an Agrónic 4000 (Sistemes Electrònics PROGRÉS, S. A., Bellpuig, Spain). The pumps were connected to 250-L tanks containing the irrigation solutions. The soil moisture level was measured by an EC5 Soil Moisture Probe (Decagon Devices, Ltd., Pullman, WA) placed in the east-facing part of the substrate at an angle of 45 , with the flat side perpendicular to the surface of the substrate. The data logger was programmed to collect data every minute from three EC5 probes per treatment and to calculate the average every 30 min. The q was obtained from the voltage readings of the soil moisture sensor using our own substrate-specific calibration (q = 3.6642*mV – 0.355; r = 0.98) determined using the procedure described by Valdés et al. (2012). Fertilization was carried out by the irrigation head, and in all treatments, nutrients were provided at constant concentrations in the irrigation water, containing 80N–17.5P–66.4K (ppm) at pH 6. This nutrient solution was made by mixing KNO3, NH4NO3, K2HPO4, and HNO3. The Received for publication 19 Aug. 2013. Accepted for publication 25 Nov. 2013. We are grateful for the financial aid received from the Ministerio de Economı́a y Competitividad and FEDER through the projects (AGL2011-30022-C02-1 and AGL2011-30022-C02-2). To whom reprint requests should be addressed; e-mail raquel.valdes@upct.es. 160 HORTSCIENCE VOL. 49(2) FEBRUARY 2014 addition of fertilizers increased the EC by 0.5 dS·m. The temperature and relative humidity were measured continuously during the experiment by a data logger (HOBO H08-00402; MicroDAQ.com, Ltd., Contoocook, NH). The average air temperature in the greenhouse was 8.3 C (minimum), 25.7 C (average), and 45.2 C (maximum); minimum relative humidity was 22.4% and the maximum 100% with a mean of 65.5%. Irrigation treatments. Six treatments resulted from irrigating with one, two, or four emitters per pot under non-saline (1.5 dS·m) and saline conditions (3 dS·m). The emitters were inserted in the center of the upper part of the four quadrants of the top circle of substrate [southeast (SE), southwest (SW), northwest (NW), and northeast (NE)]. When only one emitter was used, it was placed in the SE quadrant; when two emitters were used, they were placed in the SE and NW quadrants. In the case of four emitters, they were placed in each of the four quadrants. The treatments started the first week of Apr. 2012 (4 weeks after transplant, when the establishment phase had finished). Salinity took the form of sodium chloride added to the base nutrient solution of each tank. For all treatments, the irrigation system was triggered when the average q of the treatment with one emitter and 1.5 dS·m reached the threshold of 40% by volume. Hence, the irrigation frequency was the same for all treatments. All irrigation treatments were based on this treatment because it is the most frequently used. Furthermore, we started with the hypothesis that saline irrigation would increase the leaching fraction (as a result of the decrease in water consumption by the plant), whereas any increase in the number of emitters would increase consumption (wetter substrate), which would lead to an intermediate level of leaching. The volume of water applied in each irrigation event was based on the duration of the event, which, in the case of one emitter, produced a leaching fraction of 15% at EC 1.5 dS·m (a normal leaching fraction in this treatment). The irrigations carried out with two emitters lasted half of the time used for one emitter and when four emitters were used the time was a quarter of the time used for one emitter. Water consumption was calculated by measuring the water applied to the pots, so that in each treatment, three 1.5-L plastic bottles containing the emitter or emitters were used. From time to time, the volume of water collected in the bottles was measured in each treatment, and the sum of all these measurements was taken as the total amount of water applied. The mean quantity of water applied in the six treatments was 50.31 ± 1.08 L per pot, which is slightly below the theoretical consumption calculated for the number of irrigation events and the duration of the same (50.67 L). Measurements. The leaching fraction and leachate EC were measured in five pots of each treatment. The leachate was collected weekly throughout

The Number of Emitters Alters Salt Distribution and Root Growth in Potted Gerbera