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There is increasing interest in reducing fertilizer cost and establishing proper irrigation management for sustainable vegetable production. Nigari, an effluent of salt industries, is cheaper than commercial fertilizers. Another important vegetable production factor is nutrient application timing to improve soilless cultivation in crops like sweet pepper. Therefore, this study evaluated the effects of nigari and nutrient solution application timing on leaf gas exchanges of sweet pepper cultivated under a soilless system. Treatments included three nigari rates [no nigari plus a standard nutrient solution as control, 2 mL·L nigari + additional nitrogen–phosphorus–potassium (N–P–K) to equal the standard, and 4 mL·L nigari + additional N–P–K to equal the standard]. Three daily application timings (T1 = 0700 HR + 1500 HR, T2 = 0900 HR + 1500 HR, and T3 = 0700 HR + 0900 HR + 1500 HR) were used for each nutrient solution. Leaf gas exchange parameters were studied during the vegetative and reproductive growth stages of sweet pepper cv. Papri new-E-red. Photosynthetic responses and its related parameters, namely transpiration (E), stomatal conductance (gS), and maximum photosynthesis (Amax), were significantly affected by nigari rates and nutrient solution application timing. Photosynthesis-related parameters, E, gS, Amax, and initial slope of photosynthesis in response to light curve were the highest and light compensation point (LCP) and leaf vapor pressure deficit (LVPD) were the lowest at 2 mL·L nigari compared with the control at both plant vegetative and reproductive growth stages. For nutrient solution application timing, the highest E, gS, and Amax were observed at T3 treatment at both plant growth stages. Furthermore, marketable yield of sweet pepper was the highest when 2 mL·L nigari was applied at 0700, 0900, and 1500 HR a day. Leaf gas exchange parameters showed that nutrient solution application timing of 0700, 0900, and 1500 HR a day was better for obtaining high yield of sweet pepper under nigari treatment in soilless culture. Sweet pepper (Capsicum annuum L.) is an economically important vegetable crop all over the world. It is often grown intensively in greenhouses. In the greenhouse, irrigation is necessary to ensure stable yields with high quality. For sustainable crop cultivation, crop-specific and water-saving irrigation application timings that do not negatively affect crop productivity must be developed. Worldwide, several successful attempts have been documented regarding the use of deficit irrigation methods, namely regulated deficit irrigation and partial root zone drying, to improve irrigation water use efficiency in various crop species (Arzani et al., 2000; Dorji et al., 2005; Grant et al., 2004; Hutton, 2000; Kang et al., 2002; Kirda et al., 2004; Romero et al., 2004; Van Hooijdonk et al., 2004). However, there has been little attention paid to application timing of nutrient solution for sweet pepper in soilless culture. Russo (2011) conducted research on irrigation timing in field-grown sweet pepper. Information on how application of irrigation timing affects vegetable production in soilless culture can help growers to improve crop yield and quality of the products. Timing of the delivery of nutrient solution can affect water availability to plants and thus can directly affect fruit yield, fruit quality, and production costs. Understanding the timing of nutrient solution has therefore become increasingly important to achieve sustainable agriculture. Sustainable agricultural development depends on sound irrigation and water management, the main aim of which is, first, to satisfy crop water needs and, second, to maintain good soil aeration (McNiesh and Welch, 1985). Therefore, mistakes in application timing of nutrient solution may result in serious yield reduction. Furthermore, overirrigation and prolonged soil saturation can cause disease in plant roots or root rot. However, different irrigation timing may have an effect on yield by affecting leaf gas exchanges. There is also increasing attention being given toward reducing the production cost of agricultural crops. Nigari application in soilless culture can lower production cost because it contains many macroand micronutrients and can be an alternative fertilizer source. Nigari is an effluent of salt industries and cheaper than commercial fertilizers. It contains high amounts of calcium (Ca), magnesium (Mg), and other microelements that may have an effect on leaf gas exchange of sweet pepper. Nigari also contains some extent of sodium (Na) that may impose mild salinity, but it contains some silicon (Si) that may minimize the negative impact of salinity (Bradbury and Ahmad, 1990; Liang et al., 1996). However, the excess of salts in the soil solution and in the irrigation water causes the reduction of pepper fruit size (Navarro et al., 2002) and the increase of blossom-end rot incidence (Tadesse et al., 1999). Photosynthetic rates depend on a number of factors such as age of the leaves (Connor et al., 1993), sink assimilate demand (Frageria, 1992), and availability of water as well as light and nutrients. Photosynthesis is also affected by different stress factors (Taiz and Zeiger, 2006). The capacity of the plant’s photosynthetic apparatus is reduced in the presence of excess salts (Ashraf, 2001; RomeroAranda et al., 2001). In any case, the ultimate effect of salts on photosynthesis depends on the nature of the salts, their concentration, and the plant species. It is possible that low salinity increases photosynthesis, whereas high salinity reduces it. Nigari may have mild or low salinity as a result of the presence of Na and may have an effect on leaf gas exchange in sweet pepper. There has been no research on nigari application and its impact on leaf gas exchange, although it is used as a supplemental liquid fertilizer in Japan. There is a need to encourage more sustainable agricultural practices, reducing inputs of fertilizers, while minimizing any negative impact on leaf gas exchange of crops like sweet pepper. Therefore, it is important to investigate the effect of nigari on leaf gas exchange in sweet pepper. In the present study, leaf gas exchange of sweet pepper plants was measured to determine the effects Received for publication 21 June 2012. Accepted for publication 4 Sept. 2012. This article is a portion of a PhD dissertation that will be submitted by Md. Jahedur Rahman at the University of Miyazaki, Japan. We thank Dr. M. Mofazzal Hossain of the Horticulture at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh, for his valuable suggestions during preparing the manuscript. We also thank Kurokawa and Hanif Afzali for cooperation in collecting the data. We are grateful to Mr. Joshua Hansell for English editing. Professor. Assistant Professor. To whom reprint requests should be addressed; e-mail inden@cc.miyazaki-u.ac.jp. 1574 HORTSCIENCE VOL. 47(11) NOVEMBER 2012 of nutrient solution application timing and nigari on gS, LVPD, and leaf photosynthetic rate of soilless greenhouse-grown sweet pepper plants. Materials and Methods Experimental site, plant materials, and growing conditions. A greenhouse experiment was conducted from Sept. 2011 to May 2012 at the Horticulture Farm in the University of Miyazaki, Miyazaki, Japan. The experiment was conducted in 15-L pots and one plant was transplanted into each pot. Seedlings were transplanted into the pots on 12 Nov. 2011. Sweet pepper cv. Papri new-E-red (Marutane Seed Co., Kyoto, Japan) was used in this experiment based on its yield under high-temperature conditions (Rahman and Inden, 2012). One 15-cm, sixth-leaf stage, 8-week-old seedling was transplanted into a 15-L pot containing a 50:45:5 (v/v) mixture of coconut coir peat, perlite, and shodo (burned loam soil), respectively. Three replicates of three pots were tested for each treatment. Two edge rows were grown to reduce border effects. Nutrient solutions were applied to the plants continuously by a drip irrigation system. The pH and electrical conductivity (EC) of the nutrient solutions were controlled during application. Nutrient compositions, EC, and pH for each treatment are shown in Table 1. Average minimum and maximum temperatures and relative humidity were 18 ± 2 C and 24 ± 2 C and 40% ± 10% and 55% ± 10%, respectively, during the experiment. The temperatures were maintained by a heating system and exhaust fans in the greenhouse. Experimental design and treatments. A randomized complete block design with three 3 three factorial treatments and three replications were used in this study. Three plants served as an experimental unit. Two factors of this experiment were three nigari treatments (no nigari plus a standard nutrient solution as control, 2 mL·L nigari + additional N-P-K to equal the standard, and 4 mL·L nigari + additional N–P–K to equal the standard) and three nutrient solution application timings (T1 = twice a day at 0700 HR and 1500 HR; T2 = twice a day at 0900 HR and 1500 HR; and T3 = three times a day at 0700 HR, 0900 HR, and 1500 HR). An equal volume of nutrient solution was applied for all the treatments and it was on an average 1.95 L/plant/day. The standard nutrient solution composition was selected according to Rahman and Inden (2012). Standard nutrient solution was applied to the plants for all the treatments until 2 weeks after transplanting. After that time, nigari treatment was started and applied everyday until harvest. Nigari was obtained from Miyazaki Sun Salt Co., Miyazaki, Japan, and was analyzed by inductively coupled plasma emission spectroscopy (ICPS-8100; Shimadzu Corp., Kyoto, Japan) for its nutritional composition (Table 2). Measurements. The third fully open leaf below the shoot tip was selected from each plant for measurements of gS, E, LVPD, and net photosynthetic rate (NPR) in the plant vegetative and reproductive growth stages. These measurements for the vegetative gr

Leaf Gas Exchange Responses to Irrigation Timing and Nigari (Effluent of Salt Industries) of Sweet Pepper (Capsicum annuum L.) in Soilless Culture