Effects of salinity on fruit yield and quality of tomato grown in soil-less culture in greenhouses in Mediterranean climatic conditions

agricultural water management 95 (2008) 1041 1055 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/agwat Effects of salinity on fruit yield and quality of tomato grown in soil-less culture in greenhouses in Mediterranean climatic conditions J.J. Magán a, *, M. Gallardo b, R.B. Thompson b, P. Lorenzo c a Estación Experimental de la Fundación Cajamar, Paraje Las Palmerillas, n8 25, 04710 El Ejido, Almería, Spain b Dpto. Producción Vegetal, Universidad de Almería, La Cañada, 04120 Almería, Spain c IFAPA, Autovía del Mediterráneo, Salida 420, 04745 La Mojonera, Almería, Spain article info Article history: Received 28 September 2007 Accepted 30 March 2008 Published on line 19 May 2008 Keywords: Almeria Electrical conductivity Hydroponic Re-circulation Substrate Vegetable abstract There is increasing pressure to reduce water use and environmental impact associated with open system, soil-less production in simple, plastic greenhouses on the Mediterranean coast. This may force the adoption of re-circulation of nutrient solutions. In southeastern Spain, irrigation water is mostly from aquifers and has moderate levels of salinity. The adoption of re-circulation using moderately saline water requires detailed information of crop response to salinity, in order to optimise management. The effect of salinity on fruit yield, yield components and fruit quality of tomato grown in soil-less culture in plastic greenhouses in Mediterranean climate conditions was evaluated. Two spring growing periods (experiments 1 and 2) and one long season, autumn to spring growing period (experiment 3) studies were conducted. Two cultivars, Daniela (experiment 1) and Boludo (experiments 2 and 3), were used. Seven levels of electrical conductivity (EC) in the nutrient solution were compared in experiment 1 (2.5 8.0 ds m 1 )and five levels in experiments 2 and 3 (2.5 8.5 ds m 1 ). Total and marketable yield decreased linearly with increasing salinity above a threshold EC value (EC t ). There were only small effects of climate and cultivar on the EC t value for yield. Average threshold EC values for total and marketable fruit yield were, respectively, 3.2 and 3.3 ds m 1. The linear reductions of total and marketable yield with EC above EC t showed significant differences between experiments, the slope varying from 7.2% (autumn to spring period, Boludo ) to 9.9% (spring period, Boludo ) decreases per ds m 1 increase in EC for total yield, and from 8.1% (spring period, Daniela ) to 11.8% (spring period, Boludo ) for marketable yield. The decrease of fresh fruit yield with salinity was mostly due to a linear decrease of the fruit weight of 6.1% per ds m 1 from an EC t of 3.0 ds m 1 for marketable fruits. Reduction in fruit number with salinity made a smaller relative contribution to reduced yield. Blossomend rot (BER) increased with increasing salinity. There was a higher incidence of BER with spring grown crops, and Boludo was more sensitive than Daniela. Increasing salinity improved various aspects of fruit quality, such as: (i) proportion of Extra fruits (high visual quality), (ii) soluble solids content, and (iii) titratable acidity content. However, salinity decreased fruit size, which is a major determinant of price. An economic analysis indicated that the EC threshold value above which the value of fruit production decreased linearly with increasing salinity was 3.3 ds m 1, which was the same as that for market- * Corresponding author. Tel.: +34 950 580548; fax: +34 950 580450. E-mail address: jjmagan@cajamar.com (J.J. Magán). 0378-3774/$ see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.03.011

1042 agricultural water management 95 (2008) 1041 1055 in which s is the percent yield decrease per unit salinity increase above the threshold, and EC t is the salinity threshold (maximum root zone salinity without yield reduction). The response of tomato to increasing salinity has been characterised in a number of studies. Most of the studies with greenhouse-grown soil-less tomato have been conducted in cool climates in NW Europe, in high technology glasshouses with active climate control systems (e.g. Adams, 1989; Sonneveld and van der Burg, 1991; Willumsen et al., 1996). The response of tomato yield to salinity varies between horticultural systems, being mostly affected by climatic conditions (Sonneable yield. In the economic analysis, the value of increased visual fruit quality was offset by reduced yield and smaller fruit size. # 2008 Elsevier B.V. All rights reserved. 1. Introduction The greenhouse-based vegetable production system of southeastern (SE) Spain produces out-of-season vegetables in simple, low cost plastic greenhouses with no climate control apart from passive ventilation (Castilla and Hernández, 2005). This vegetable production system has expanded rapidly along the Spanish Mediterranean coast in the last 30 years. There are currently 45,000 ha of greenhouses (Castilla and Hernández, 2005) in this region, with 27,000 ha in the province of Almeria. Similar vegetable production systems are being developed in other countries with similar climatic conditions, most notably in Mexico and Morocco, and also in other Mediterranean and Latin American countries. In the greenhouse production system of SE Spain, crops are grown in either soil or soilless culture. The surface area of soil-less greenhouse crops has expanded rapidly since the 1990s, and in the province of Almeria there are currently more than 5000 ha (Pérez-Parra and Céspedes, 2001). Almost all soil-less cropping systems are open systems, in which there is no collection and recirculation of drainage from containers (usually bags) of substrate, and all drainage freely enters the underlying soil. Tomato and pepper are the two major crops in this cropping system, the relative importance each year being determined by price. This cropping system is a major provider of tomato to Western Europe. In the province of Almeria, there are almost 10,000 ha of tomato (Consejería de Agricultura y Pesca, 2007), of which almost 2000 ha were estimated, in a recent survey, to be grown in soil-less culture (A. Céspedes, personal communication). Tomato is grown from late summer to spring (autumn to spring period) or from winter to late spring or early summer (spring period). In SE Spain, the supply of water is a major limiting factor for crop production. Most of the water used for greenhouse-based vegetable production comes from over-exploited aquifers. Moreover, there is increasing demand for the limited water resources from rapidly developing real estate and tourism industries. Nearly all of the areas where the greenhouses are located have been declared nitrate vulnerable zones in accordance with the European Union (EU) Nitrate Directives (Anonymous, 1991), and are consequently required to reduce aquifer nitrate pollution. Additionally, the recent EU Water Directive (Anonymous, 2000) requires that subterranean waters of member states be clean by 2015. Considering these factors, there is considerable pressure to maximise water use efficiency and to minimise pollution of groundwater associated with greenhouse-based vegetable production in SE Spain. A fundamental management consideration for soil-less growing systems is the requirement to maintain the salinity of the root zone solution at levels which are not detrimental to optimal crop production (Sonneveld, 2000). To avoid problems caused by accumulation of salts, an appreciable proportion of applied nutrient solution is drained (van Os, 1995). In commercialsoil-lessvegetableproductioninsespain, leachingfractions of 30 40% of applied water are normally used. This represents both a substantial loss of water and a major source of nitrate pollution of groundwater. It is likely, that there will be political pressure to convert open soil-less systems into closed soilless systems in which all drainage is collected and re-circulated, as has occurred in north-western (NW) European countries. In SE Spain, the moderate salinity of irrigation water obtained from aquifers will be a major practical consideration regarding the adoption of closed soil-less systems. The salinity of water used for irrigation in SE Spain varies appreciably, with electrical conductivity (EC) being mostly between 0.5 and 5 ds m 1. This contrasts the situation in NW European countries, such as The Netherlands, where abundant rainfall ensures a supply of very low EC water. The initial EC of irrigation water determines the range available for EC increase, which occurs firstly by nutrient addition, and then by salt accumulation during repeated cycling of the nutrient solution through the root zone of substrate-grown crops. Most vegetable crops are sensitive or moderately sensitive to salinity, and yield reductions are expected with moderate levels of salinity in the root solution (Maas and Hoffman, 1977). In order to prevent reductions in yield, the adoption of closed soilless systems in SE Spain, will probably require periodic discharges of the re-circulating nutrient solution to maintain salinity in the root zone below critical levels (Magán et al.,2005), thereby forming semi-closed systems. Salinity will need to be managed to ensure that yield and quality are maintained, while minimising the proportion of nutrient solution discharged. To achieve this, detailed knowledge of the crop response to salinity is required. Also, for tomato grown in open soil-less cultivation in SE Spain, knowledge of the response to salinity is required to optimise the yield of fruit and fruit quality. In general terms, the response of tomato yield to increasing salinity follows the Maas and Hoffman model (Maas and Hoffman, 1977; Eq. (1)), with a linear reduction after a threshold of root zone electrical conductivity has been reached. Relative yield (Y r ), expressed as a percentage, for a given average root zone salinity (EC e ) exceeding this threshold can be calculated by: Y r ¼ 100 sðec e EC t Þ (1)

agricultural water management 95 (2008) 1041 1055 1043 veld and Welles, 1988; Li et al., 2001; Claussen, 2005). Given (i) the high economic importance of tomato production in greenhouses in SE Spain, (ii) the lack of relevant data for these growing conditions, and (iii) the increasing pressure to reduce environmental impact and water use, it is important to characterise the response of tomato to salinity for the growing conditions in simple plastic greenhouses on the Mediterranean coast of SE Spain. Additionally, in most published studies examining salinity responses in tomato, the number of treatments compared has been limited, with the maximum number being only four (e.g. Adams and Ho, 1989; van Ieperen, 1996; Tüzel, 2002). To accurately characterise the response of yield and quality to increasing EC, it is necessary to have an appreciable number of EC treatments within the range of EC likely to be encountered in commercial tomato production. The objective of this work was to assess the effects of increasing salinity on fruit yield, yield components, several quality parameters and the economic value of the yield of tomato grown in simple plastic greenhouses in SE Spain. Five or seven different levels of salinity were compared in three consecutive experiments conducted under conditions similar to commercial greenhouse production. This information will enable the determination of EC threshold values that optimise yield, quality and growers incomes, when re-circulation of nutrient solutions is adopted in soil-less growing systems in this region, particularly when lower quality (higher EC) water is used. It will also assist in the management of open soil-less systems, where lower quality water is used. 2. Materials and methods 2.1. Location and cropping details Three experiments were conducted at the field research station of the Cajamar Foundation, in El Ejido, Almeria province, in SE Spain (2843 0 W, 36848 0 N and 151 m elevation) in two different multi-span greenhouses with polyethylene cover and without active climate-control systems. The greenhouses measured 85 m long by 22.5 m wide (first experiment) and 40 by 24 m (second and third experiments). The two greenhouses had an east-west orientation, with crops rows aligned north-south. General information about the experiments is presented in Table 1. Tomato (Lycopersicon esculentum Mill) was grown in the three experiments but the growing period and cultivar varied between experiments. Experiments 1 and 2 both had a spring growing period and cultivars were, respectively, Daniela and Boludo. The third crop had a long, autumn to spring growing period from late summer to spring and the cultivar was Boludo. The crops were grown in 28 L styrofoam containers, measuring 37 cm 27 cm 28 cm deep, filled with perlite (3 6 mm diameter), which were placed in gutters for the collection and re-circulation of drainage. Seedlings were grown in rockwool cubes and transplanted before the inflorescence of the first truss was visible. In experiment 1, five plants were grown per styrofoam container; in experiments 2 and 3, there were four plants per container. In experiment 1, styrofoam containers were placed every 85.7 cm and, in experiments 2 and 3, every 1 m. Plant density was 2.92 plants m 2 in experiment 1, and 2 plants m 2 in the experiments 2 and 3. The distance between adjacent rows of styrofoam containers was 2 m in each experiment. Plants were vertically supported by nylon cord guides, and were pruned and managed following local practices. Regular pruning was conducted such that all auxiliary shoots were removed and only the main stem was left. Plants were topped at 96, 116 and 181 days after transplanting (DAT) in the experiments 1, 2 and 3, respectively. The nutrient solution was applied by a drip irrigation system with two emitters per container with a discharge rate of 8 L h 1 per emitter. The nutrient solution was re-circulated; Table 1 Description of the three experiments: the growing period, date of transplanting, date of end of crop, the duration of the growing period, the cultivar, and the target electrical conductivity (EC), and average measured EC during the experiment for each treatment in each experiment Experiment No. Growing period Date of transplanting End of crop Duration (days) Cultivar Treatment No. Target EC (ds m 1 ) Average measured EC (ds m 1 ) 1 Spring 2000 3/2/00 6/7/00 154 Daniela 1 2.5 2.7 2 3.0 3.2 3 4.0 4.1 4 5.0 5.1 5 6.0 5.8 6 7.0 7.0 7 8.0 7.8 2 Spring 2002 27/12/01 28/6/02 183 Boludo 1 2.5 2.6 2 3.0 3.0 3 4.0 3.9 4 6.0 5.9 5 8.0 7.7 3 Autumn to Spring 2002/03 10/9/02 3/6/03 266 Boludo 1 2.5 2.7 2 4.0 4.0 3 5.5 5.5 4 7.0 6.9 5 8.5 8.4

1044 agricultural water management 95 (2008) 1041 1055 Table 2 Target electrical conductivity (EC) and average composition of the re-circulating solution for the different treatments in each experiment Experiment No. Target EC (ds m 1 ) NH 4 + K + Ca 2+ Mg 2+ NO 3 SO 4 2 H 2 PO 4 Na + 1 2.5 0.1 5.3 6.5 3.0 20.9 1.6 1.2 3.4 0.9 3.0 0.1 5.3 7.4 3.6 24.1 2.4 1.3 6.0 2.0 4.0 0.1 6.3 7.6 3.9 25.5 2.6 1.1 12.6 7.3 5.0 0 5.1 8.6 5.1 27.7 2.8 1.1 21.7 14.9 6.0 0 4.8 8.7 3.8 26.2 2.7 1.3 28.5 23.4 7.0 0 5.7 8.7 4.4 28.1 3.1 1.1 35.8 30.4 8.0 0 5.6 8.4 4.5 27.4 3.0 1.0 51.1 40.2 2 2.5 0 4.9 6.0 3.0 18.1 3.6 0.9 5.4 1.1 3.0 0 5.2 5.6 2.8 16.9 4.1 0.8 10.8 5.2 4.0 0 4.6 6.4 3.4 20.6 3.3 0.8 17.0 11.9 6.0 0 5.1 6.6 3.4 21.1 3.8 0.7 35.7 29.3 8.0 0 4.9 6.8 2.7 20.7 5.1 0.6 57.0 46.4 3 2.5 0 2.4 6.6 3.5 16.4 3.6 1.7 5.6 2.4 4.0 0 3.0 6.8 4.1 17.7 4.8 1.7 16.4 11.2 5.5 0 3.6 6.9 4.3 19.9 4.9 1.6 29.2 22.8 7.0 0 2.3 6.8 4.3 18.6 4.9 1.7 44.7 37.8 8.5 0 3.0 7.1 4.5 21.5 4.6 1.3 57.6 50.7 Cl with the nutrient solution being replaced when it became difficult to maintain the target EC of the corresponding treatment. The leaching fraction was around 90%, which enabled the maintenance of very similar EC in both the root zone and drainage solutions for a given treatment. To obtain such a high leaching fraction it was necessary to apply as many as 200 irrigations per day, each of 250 ml per emitter, during periods of largest water requirements. The plastic cover of the greenhouse was white-washed (application of CaCO 3 suspension) in experiments 1 and 3 (on 26th April 2000 and 15th April 2003, respectively), but not in experiment 2. 2.2. Treatments and experimental design In the three experiments, a nutrient solution with an EC of 2.5 ds m 1 was compared to several nutrient solutions with a range of higher salinity (Table 1). The 2.5 ds m 1 nutrient solution was representative of nutrient solutions in this region that use better quality irrigation water, derived from aquifers, which commonly has an EC of around 0.5 ds m 1. The addition of fertilisers to form a complete nutrient solution generally results in an increase of approximately 2.0 ds m 1. The levels of salinity examined varied between individual experiments (Table 1). Hereafter, the 2.5 ds m 1 nutrient solution, in each experiment, will be referred to as treatment 1, and the other treatments in order of increasing EC as treatments 2, 3, 4, etc. (Tables 1 and 2). The nutrient solution of treatment 1 had low sodium and chloride concentrations of <6 mm(table 2). The increase in EC in the various higher salinity treatments was obtained by adding sodium chloride to a nutrient solution similar to that used in treatment 1. The salinity treatments were managed to maintain the measured EC value, throughout each experiment, at 0.5 ds m 1 of the target EC value, and to maintain similar concentrations of each nutrient (except sodium and chloride) in all treatments within each experiment (Tables 1 and 2). The salinity treatments were initially established by gradually adding sodium chloride to the nutrient solutions during a 7 10 day period commencing 1 or 2 weeks after transplanting. Sodium chloride was used for increasing salinity because in the cropping conditions of SE Spain, the accumulation of both sodium and chloride is a major consideration in the management of re-circulating solutions in soil-less cropping. In experiment 1, the experimental design was a randomised block design. The greenhouse was divided into 28 experimental plots, with 14 plots on either side of a central passage (Fig. 1). There were four blocks, each with seven plots, with two blocks on either side of the passage. Each plot consisted of a row of 35 plants in seven individual styrofoam containers (five plants per container), with the 25 plants of the five central containers being used for measurements. The five plants (one container) at the northern and southern ends of each row, in each replication, formed borders. There were two border rows of containers (each with five plants) on both the eastern and western sides of the experimental area. In the experiments 2 and 3, the experimental design was a nested factorial design. The treatments were allocated to five contiguous rows of styrofoam containers in the eastern part of the greenhouse (Fig. 1). The rest of the greenhouse was used for destructive measurements that are not included in the present paper. There were 16 styrofoam containers, each with four plants, in each row. Individual plots consisted of 16 plants in four styrofoam containers. Treatments were applied to individual rows, with the four replications of a treatment being distributed within the same row. At the southern and northern ends of each row, there were, respectively, three and two styrofoam containers, each with four plants acting as borders. There were at least two border rows of plants on either side of the experimental area. 2.3. Management of salinity treatments The level of salinity for each treatment (Tables 1 and 2) was maintained by the use of a high leaching fraction and discharge of part of the re-circulating nutrient solution when

agricultural water management 95 (2008) 1041 1055 1045 The volume of re-circulating solution within these tanks was maintained by the use of a float valve which regulated the entry, by gravity, of fresh nutrient solution, to replace the volume transpired by the crop. From the individual mixing tanks, the nutrient solution was pumped to the drip irrigation system of the corresponding treatment. The fresh nutrient solutions for each treatment were manually prepared each week, in such a way that the concentration of each nutrient was similar to the corresponding uptake concentration of the crop (Sonneveld, 2000) during the previous week. This ensured minimal oscillation in the concentration of the different ions in the re-circulating solutions over time. To calculate weekly uptake concentrations of all nutrients for each treatment, weekly balances were calculated each week for each nutrient. Nutrient concentrations were determined each week using standard laboratory methods (M.A.P.A., 1994). The average composition of the re-circulating solution for the different treatments in each experiment is presented in Table 2. 2.5. Measurements Fig. 1 Plan of the greenhouses used for the experiments. (A) Greenhouse corresponding to experiment 1. (B) Greenhouse corresponding to experiments 2 and 3. Measurements are expressed in meters. The areas limited by a line correspond to the different replications used for measurements. The symbols B, T1, T2, T3, T4, T5, T6 and T7 indicate the rows corresponding to border, treatment 1, treatment 2, treatment 3, treatment 4, treatment 5, treatment 6 and treatment 7, respectively. necessary (generally 30 50% of the volume of the re-circulating solution was replaced with fresh nutrient solution when EC increased to >0.5 ds m 1 above the target value. This occurred twice in the spring period studies (experiments 1 and 2), and three times in the autumn to spring period study (experiment 3)). The high leaching fractions of 90% ensured that the salinity of the drainage solution was very similar to that in the root environment (de Kreij, 1999; Li et al., 2001). Samples of drainage water from each treatment were collected daily, and were analysed for EC and ph. For each experiment, average EC and ph values were calculated for the duration of the crop, from daily values. 2.4. Description of the fertigation system Each treatment had a completely independent fertigation system to avoid mixing of the different re-circulating solutions. Drainage was collected in an underground mixing tank. 2.5.1. Climatic conditions Climatic parameters were continuously monitored within the greenhouses. In experiment 1, air temperature and relative humidity (RH) were measured every 15 min with a shaded sensor located at 1.5 m height (model HOBO Pro RH/Temp, H08-032-08, Onset Computer Corporation, Bourne, Maine, USA). Solar radiation (SR) was measured every 10 min with a pyranometer (model SKS1110, Skye Instruments, Llandrindod Wells, Wales, UK) placed inside the greenhouse above the crop on the central roof span. In experiments 2 and 3, air temperature and relative humidity were measured at the same level as the highest part of the crop every 5 s with a ventilated psychrometer (model 1.1130, Thies Clima, Goettingen, Germany) and measurements were recorded every 5 min. Photosynthetic active radiation (PAR) was measured every minute by four PAR sensors (Ha-Li, EIC, Madrid, Spain) placed inside the greenhouse, above the crop and were uniformly distributed across the central span to register the spatial variation of radiation inside the greenhouse. PAR radiation was converted to solar radiation using the equation developed by Medrano et al. (2001) for Mediterranean plastic greenhouses. Radiation data presented are the average of the four sensors. For each experiment, vapor pressure deficit (VPD) was calculated from air temperature and relative humidity data. 2.5.2. Fruit yield and fruit quality Red fruit was harvested weekly in the three experiments. Fruit yield was determined on four replicate plots of 25 plants each in the experiment 1, and on four replicate plots of 16 plants each in the experiments 2 and 3. Fruits were classified as marketable or un-marketable. Marketable fruit yield was classified according to EU marketing regulations (EU 790/2000 and EU 717/2001) using the criteria of: (i) size, with four categories, MM, M, G and GG (47 57 mm, 57 67 mm, 67 82 mm, 82 102 mm diameter, respectively), and (ii) external appearance in 3 categories: Extra (fruits of high quality, firm and with the representative shape and development of the cultivar), I (firm fruits of good quality, with small defects of

1046 agricultural water management 95 (2008) 1041 1055 shape, development or colour) and II (firm fruits with moderate defects of shape, development or colour, with small bruises, or with healed wounds of a maximum of 3 cm length). Un-marketable fruit yield was classified according to the nature of the blemish: fruits with cracking, with blossom-end rot (BER), with blotchy ripening, deformed fruits, small fruits and others. For each group, fresh weight of individual fruits and number of harvested fruits were determined. Ten marketable fruits per replicate plot were randomly selected every 2 weeks to assess organoleptic fruit quality. These fruits were juiced with a domestic juicer, and the juice was decanted. The decanted juice was analysed for total soluble solids (Brix index), ph and titratable acidity. Total soluble solids content was measured with a digital refractometer (model No. 160, Shibuya Optical Co. Ltd., Wako-shi, Saitama Pref., Japan). ph was measured with a ph meter (model HI 9024, Hanna Instruments Inc., Ann Arbor, Michigan, USA). Titratable acidity was determined by titration with 0.1 M NaOH. 2.6. Data analysis Data of total and marketable fruit yield, yield components and the economic value of yield (described subsequently) in response to increasing salinity were analysed using the Maas and Hoffman conceptual model (Maas and Hoffman, 1977). With this model, a maximum value is maintained until a threshold EC value (EC t ) is reached, after which there is a linear decrease with increasing salinity. A modification of this model was used to analyse the incidence of BER; a minimum value was maintained until the threshold EC value, after which a linear increase with increasing salinity was obtained. For the Maas and Hoffman analysis, mathematical and statistical analyses were used to identify (a) the horizontal line representing maximum values, (b) the linear regression representing the decline of the parameter with increasing salinity, and (c) the threshold (EC t ) value. These analyses related the measured parameters to average EC during the growing period. To determine maximum values, an analysis of variance (ANOVA) was conducted to identify which treatments did not have statistically significant differences; the average of those treatments represented the intercept of the horizontal line. Subsequently, data of fruit yield, yield components and economic value of yield were expressed as relative values as the percentage of the corresponding maximum value. To determine the slope of the reduction of the relative values with increasing salinity, a series of linear regressions were conducted to select the complete group of treatments, to the right of possible threshold values, with the highest coefficient of determination (r 2 ) value. The threshold value (EC t ) was the intersection of this regression line with the horizontal line representing maximum values (as 100% of maximum value). Fruit organoleptic quality data were expressed as the percentage of values from treatment 1. Linear regression analysis, using data from all treatments, was used to determine the variation attributed to increasing salinity. 2.6.1. Statistical analyses Statistical analyses were conducted with Statgraphics Plus ver. 4.1 (Manugistics Inc., Rockville, Maryland, USA). The previously mentioned linear regressions were compared between experiments for statistically significant differences (P < 0.05) in slope values. Comparison of absolute values for yield, fruit number and fruit weight was conducted with analysis of variance and Duncan s multiple range test. 2.6.2. Economic analysis An economic analysis was conducted to evaluate the overall effect of salinity on the economic value of fruit yield. This economic analysis assessed the effect of salinity on fruit yield, fruit size and external appearance, using results from the present experiments. Organoleptic quality was not considered because it is not considered in current pricing mechanisms. Prices, averaged over a 6-year period for each fruit size and external appearance category, were obtained from the marketing co-operative CASI, which is the largest wholesale retailer of tomato produced in the region of Almeria. The economic value of fruit yield was calculated for all EC levels examined in the three experiments as the sum of the value of all categories. 3. Results 3.1. Climatic conditions Average values for 24 h periods of mean, maximum and minimum air temperature and vapor pressure deficit (VPD), for day-light periods of mean air temperature and mean VPD, Table 3 For each experiment, average values throughout the cropping period for each experiment for (i) 24-h mean, maximum and minimum air temperatures and vapor pressure deficit (VPD), and (ii) daylight period mean air temperature and VPD, and (iii) average 24-h integral of solar radiation (SR) Temperature (8C) VPD (kpa) SR Ave. day-light mean (8C) Ave. 24-h mean (8C) Ave. 24-h max. (8C) Ave. 24-h min. (8C) Ave. day-light mean (kpa) Ave. 24-h mean (kpa) Ave. 24-h max. (kpa) Ave. 24-h min. (kpa) Average 24-h integral (MJ m 2 d 1 ) Experiment 1 23.5 20.4 27.0 14.8 1.35 0.94 2.05 0.23 10.4 Experiment 2 21.0 17.2 25.7 11.2 1.07 0.66 1.81 0.10 12.4 a Experiment 3 20.8 16.9 25.5 11.2 0.79 0.47 1.46 0.07 7.8 a a Radiation measured as PAR (mol m 2 day 1 ) and converted to solar radiation (MJ m 2 day 1 ) according to Medrano et al. (2001).

agricultural water management 95 (2008) 1041 1055 1047 Fig. 2 Relationship between electrical conductivity of the drainage solution and the total (A) and marketable (B) fruit yield expressed as percentages of the maximum value in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). The straight lines show the best-fit linear regression using the Maas and Hoffman model (( ) experiment 1; (- - -) experiment 2; ( ) experiment 3). All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates. and the average daily integral of solar radiation, inside the greenhouse for the growing periods of the three experiments are presented in Table 3. The lower air temperature, VPD and solar radiation in experiment 3 reflect the autumn to spring growing period of this crop. Air temperature and VPD were higher in experiment 1 than in 2 despite receiving less solar radiation (Table 3). The larger window surface area and more effective window design in the greenhouse used in experiment 2, compared to experiment 1, were associated with smaller temperature increases. Additionally, the application of whitewash considerably reduced incoming solar radiation in experiments 1 and 3. In general, values of temperature and VPD were within the normal range for plastic greenhouses, without active climate-control systems, on the Mediterranean coast. Table 4 Effect of electrical conductivity (EC) on total fresh fruit yield, marketable fresh fruit yield, total fruit number, marketable fruit number, average fruit weight, and average marketable fruit weight Experiment 1 Measured EC (ds m 1 ) 2.7 3.2 4.1 5.1 5.8 7.0 7.8 Total yield (kg m 2 ) 20.4a 20.6a 20.1a 18.3b 16.3c 14.6d 13.5d ** Marketable yield (kg m 2 ) 17.4bc 18.7a 18.2ab 16.9c 15.0d 13.4e 12.2f ** Total fruit number (fruit m 2 ) 154 161 164 158 157 155 151 n.s. Marketable fruit number (fruit m 2 ) 131d 145ab 147a 146ab 142ab 139bc 133cd ** Fruit weight (g) 132a 128a 123b 115c 104d 94e 89f ** Marketable fruit weight (g) 133a 129a 124b 116c 105d 96e 92f ** Experiment 2 Measured EC (ds m 1 ) 2.6 3.0 3.9 5.9 7.7 Total yield (kg m 2 ) 22.0a 22.3a 20.1b 15.9c 14.3d ** Marketable yield (kg m 2 ) 19.1a 19.3a 17.6b 12.9c 12.1c ** Total fruit number (fruit m 2 ) 145a 147a 140b 136c 137c * Marketable fruit number (fruit m 2 ) 126a 128a 123a 105c 114b ** Fruit weight (g) 152a 152a 143b 117c 105d ** Marketable fruit weight (g) 151a 151a 143b 123c 106d ** Experiment 3 Measured EC (ds m 1 ) 2.7 4.0 5.5 6.9 8.4 Total yield (kg m 2 ) 27.7a 26.3b 22.3c 19.4d 16.8e ** Marketable yield (kg m 2 ) 25.2a 23.8b 19.9c 16.9d 13.8e ** Total fruit number (fruit m 2 ) 212a 211a 204ab 201bc 192c ** Marketable fruit number (fruit m 2 ) 181a 181a 169b 160b 145c ** Fruit weight (g) 131a 124b 109c 96d 87e ** Marketable fruit weight (g) 140a 131b 118c 105d 95e ** n.s., *, **: non-significant differences according to variance analysis, significant difference at P < 0.05, significant difference at P < 0.01. Different letters in the same row indicate a significant difference according to Duncan s test (P < 0.05).

1048 agricultural water management 95 (2008) 1041 1055 Table 5 For each of the three experiments, threshold values of electrical conductivity (EC t ), slope values, confidence intervals, for slope, with 95% probability, and coefficient of determination (r 2 ) for the linear regressions describing effect of (a) EC on relative total fruit yield and relative marketable fruit yield, (b) EC on relative average total fruit weight and relative average marketable fruit weight, and (c) EC on relative total fruit number and relative marketable fruit number, plus the average EC t and slope values for all experiments Total fruit yield EC t Slope Confidence intervals Marketable fruit yield r 2 EC t Slope Confidence intervals r 2 Lower Upper Lower Upper (a) Experiment 1 3.6 8.1ab 9.2 7.1 0.92 3.7 8.1a 9.3 7.0 0.90 Experiment 2 3.1 9.9b 11.3 8.6 0.96 3.1 11.8b 13.5 10.1 0.96 Experiment 3 2.9 7.2a 8.0 6.4 0.95 3.0 8.2a 9.1 7.3 0.95 Statistically significant n.a. * n.a. ** Average value 3.2 3.3 Average individual fruit weight total fruit EC t Slope Confidence intervals Average individual fruit weight marketable fruit r 2 EC t Slope Confidence intervals r 2 Lower Upper Lower Upper (b) Experiment 1 3.1 6.7 7.3 6.1 0.95 3.0 6.4 7.0 5.9 0.96 Experiment 2 3.1 8.1 9.8 6.5 0.92 3.1 6.5 7.8 5.2 0.93 Experiment 3 2.9 6.2 6.7 5.6 0.97 2.8 5.7 6.1 5.3 0.98 Statistically significant n.a. n.s. n.a. n.s. Average value 3.0 6.5 3.0 6.1 Fruit number total fruit EC t Slope Confidence intervals Fruit number marketable fruit r 2 EC t Slope Confidence intervals r 2 Lower Upper Lower Upper (c) Experiment 1 5.9 1.9 3.0 0.8 0.43 5.4 3.2a 5.6 0.8 0.47 Experiment 2 2.6 2.1 3.3 0.8 0.47 3.7 7.6b 9.5 5.6 0.94 Experiment 3 4.6 1.9 3.0 0.9 0.55 4.1 4.4a 5.7 3.2 0.81 Statistically significant n.a. n.s. n.a. * Average value 4.4 2.0 4.4 n.a., n.s., *, **: not applicable, no significant differences between the slopes of the regression straight lines, significant differences at P < 0.05, significant differences at P < 0.01. Different letters in the same column indicate a statistically significant difference (P < 0.05). 3.2. Fruit yield 3.2.1. Total and marketable yield Total and marketable fresh fruit yield decreased significantly with increasing salinity in each of the three experiments (Fig. 2, Table 4). The effects of salinity on both total and marketable fruit yield clearly followed the Maas and Hoffman model (Maas and Hoffman, 1977). Total and marketable yield generally remained constant until an EC threshold value of between 3 and 4 ds m 1, depending on the experiment, and then decreased linearly with further increases in EC (Fig. 2). Throughout the harvesting period, the absolute differences in fruit yield between treatments increased progressively, even in winter (data not presented). In experiment 1, the significantly smaller marketable fruit yield of treatment 1 (EC of 2.7 ds m 1 ) compared to the 3.2 ds m 1 treatment (Table 4) was due to the higher incidence of blotchy ripening, which increased the proportion of unmarketable fruits. In experiment 2, fruit yield of the 8 ds m 1 treatment (open square, Fig. 2) was anomalous with respect to the linear regressions obtained with the other treatments; this effect was most apparent with marketable fruit yield (Fig. 2). In this treatment, an unintended reduction in EC of approximately 1 ds m 1 occurred during 10 days (95 105 DAT), which coincided with a period of low evaporative demand. This resulted in less fruit with blossom-end rot than expected from the incidence in other treatments in the same experiment. Consequently, the 8 ds m 1 treatment was not included in any of the regression analyses of data from experiment 2. Threshold EC values for total fruit yield for experiments 1, 2 and 3 were, respectively, 3.6, 3.1 and 2.9 ds m 1 (Table 5a), with an average of 3.2 ds m 1. Threshold EC values for marketable fruit yield for experiments 1, 2 and 3 were, respectively, 3.7, 3.1, and 3.0 ds m 1 (Table 5a), with an

agricultural water management 95 (2008) 1041 1055 1049 Fig. 3 Relationship between electrical conductivity of the drainage solution and the average total (A) and marketable (B) fruit weight (1) and fruit number (2) expressed as percentages of the maximum value in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). The straight lines show the best-fit linear regression ( ) experiment 1; (- - -) experiment 2; ( ) experiment 3). All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates. average of 3.3 ds m 1. In experiments 2 and 3, with the same cultivar, yield EC t values were almost identical despite different growing seasons. There were significant differences between experiments in the relative decrease in total fruit yield with increasing EC above EC t (Table 5a); the reduction of experiment 2 (9.9% per ds m 1 above EC t ) was significantly higher than that of experiment 3 (7.2%). For marketable fruit yield, the slope of the yield decrease in experiment 2 of 11.8% was significantly different from that of experiments 1 and 3, which were, respectively, 8.1 and 8.2% (Table 5a). This indicated that both cultivar and climate influenced the decrease in relative yield with increasing salinity. The larger reduction in fruit yield in experiment 2 resulted from the higher incidence of BER in fruits in the more saline treatments of experiment 2. 3.2.2. Yield components Reduced total and marketable fruit yield with increasing salinity was a consequence of reductions in fruit fresh weight and fruit number (Table 4). Both fruit weight and fruit number showed a threshold response with a subsequent linear decrease at higher EC values (Fig. 3). Fruit weight was more sensitive to increasing salinity, having lower EC t values and larger slope values than fruit number. Threshold values for average fruit weight were 3.0 ds m 1 for both total and marketable fruit (Table 5b), and for fruit number, EC t were 4.4 ds m 1 for both total and marketable fruit (Table 5c). Averaged over the three experiments, reductions in fruit weight were 6.5 and 6.1% per ds m 1, respectively, for total and marketable fruit (Table 5b); with no significant differences between experiments. The corresponding value for total fruit number was 2.0% per ds m 1. As observed for yield, EC t values for total and marketable fruit number were higher in experiment 1 than in experiments 2 and 3 (Table 5c). The slope of the reduction in the number of marketable fruits with increasing EC above EC t was lowest in experiment 1, as a consequence of the lower incidence of blossom-end rot (Fig. 4). The differences in fruit number between treatments increased with the length of the growing period (Table 4). 3.2.3. Fruit blemishes The two tomato cultivars used behaved differently with respect to the blemishes responsible for fruit being unmarketable. The cultivar Daniela (experiment 1) was sensitive to blotchy ripening at low EC (data not shown), whereas the cultivar Boludo (experiments 2 and 3) was sensitive to blossom-end rot under conditions of higher salinity (Fig. 4).

1050 agricultural water management 95 (2008) 1041 1055 Fig. 4 Relationship between electrical conductivity of the drainage solution and the weight of fruit with blossomend rot (BER) expressed as the percentage of total fruit yield of each treatment in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). The straight lines show the best-fit linear regression (( ) experiment 1; (- - -) experiment 2; ( ) experiment 3). All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates. The percentage of fruits with BER, with respect to total fruit yield, increased linearly with salinity above a threshold EC in each experiment (Fig. 4). Below the threshold value, the percentage with BER was constantly very low. Boludo was more susceptible (experiments 2 and 3) than Daniela (experiment 1), having a lower threshold EC for BER (3.0 3.7 versus 4.4 ds m 1 ) and a larger relative increase in fruit with BER with increasing EC. For spring growing periods, Boludo had a 5.0% relative increase in BER per ds m 1 compared to 1.1% for Daniela. The higher evaporative demand in experiment 2, compared to experiment 3, probably increased the incidence of BER. Although EC t values were relatively similar (3.7 and 3.0 ds m 1, respectively), the slope of increase above EC t was significantly higher in experiment 2 (5.0 versus 1.7% per ds m 1 ). 3.3. Fruit quality 3.3.1. Size and external appearance The decrease in the size of marketable fruit with increasing salinity (Fig. 5) was consistent with the reduction in fruit weight (Fig. 3). The percentage of the smallest size fruit (category MM ; 47 57 mm) increased exponentially with salinity (Fig. 5). The response of the percentage of the second smallest size (category M ; 57 67 mm) to EC was parabolic with a maximum occurring at an EC of approximately 6dSm 1 (Fig. 5). By contrast, the second largest size (category G ; 67 82 mm) reduced linearly, and the largest size (category GG ; 82 102 mm) reduced exponentially, as EC increased (Fig. 5). The predominant size categories at low EC were G and M, and at higher EC were M and MM. In both cases, the predominant size categories represented approximately 90% of marketable fruit yield, of which approximately half was in each of the two categories referred to for each case. The effect of salinity on the distribution of external appearance categories of marketable fruit is presented in Fig. 6. In general, increasing EC increased the percentage of category Extra and decreased the percentage of category II, whereas the percentage of category I remained relatively constant. In the three experiments, the largest relative increase in category Extra, in response to increasing EC, was observed in experiment 3 (Fig. 6). This was related to the appearance of an appreciable number of partially hollow fruits at lower EC in winter, which were generally classified as category II ; this condition was not apparent at higher EC. The lowest increase in the percentage of category Extra occurred in experiment 1 (Fig. 6) because a relatively high percentage of category Extra fruits occurred at low salinity. This may have been because the cultivar used in experiment 1 ( Daniela ) produced fruit with a generally better appearance than the cultivar used in experiments 2 and 3 ( Boludo ). 3.3.2. Organoleptic quality In the three experiments, the organoleptic quality of marketable fruit improved significantly with increasing salinity. Soluble solids content and titratable acidity increased linearly with EC, whereas ph decreased linearly (Fig. 7). When each of these quality parameters was expressed as relative values of treatment 1, the fitted linear regressions in each of the three experiments were not statistically different from one another. Considering the three experiments together, soluble solids content and titratable acidity increased by, respectively, 5.4 and 9.2% per ds m 1, whereas ph decreased by 0.7% (Fig. 7). Therefore, soluble solids content and titratable acidity were much more responsive to increasing salinity than ph. 3.4. Economic analysis The economic value of fruit yield decreased linearly with increasing salinity following a threshold response (Fig. 8) similar to that of fruit yield. The respective economic threshold values of 3.7, 3.2 and 3.0 ds m 1 for experiments 1, 2 and 3, with an average value of 3.3 ds m 1, were very similar to those for marketable yield. The slope of decrease in economic value was similar in the two spring growing periods, being, respectively, 11.4 and 12.0% for experiments 1 and 2. The slope for the autumn to spring growing period of 8.0% was significantly smaller. The larger relative reduction in economic value in the spring growing periods was due to the smaller improvement in visual appearance that occurred in the spring compared to autumn to spring growing periods. 4. Discussion The results of the present studies showed that the fresh fruit yield of tomato grown in simple plastic greenhouses on the Mediterranean coast was reduced by increasing salinity, in accordance with the Maas and Hoffman model (Maas and

agricultural water management 95 (2008) 1041 1055 1051 Fig. 5 Relationship between electrical conductivity of the drainage solution and the weight of fruits of different size categories ( MM, M, G and GG ) expressed as the percentage of marketable fruit yield of each treatment in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). The lines show the best-fit linear, exponential or polynomial equation in each case. All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates. Hoffman, 1977). The average EC t value for marketable yield was 3.3 ds m 1. Maas and Hoffman (1977) reported, for open field tomato grown in soil, an EC t of 2.5 ds m 1 in saturated soil extract, which is equivalent to 3.8 ds m 1 in the soil solution using the conversion proposed by Sonneveld et al. (1990). Therefore, the EC t value for marketable yield in the present work is similar to that reported by Maas and Hoffman (1977). Most published EC t values for yield of soil-less tomato crops are from greenhouses in cooler climates with appreciably less radiation, in north-western (NW) Europe. There is considerable variation in yield EC t values (root zone EC) in these studies, with values of 2.5 3 ds m 1 being reported by Sonneveld and Welles (1988), and Sonneveld and van der Burg (1991), while appreciably higher values of 5 6 ds m 1 were reported by Adams (1989), Gough and Hobson (1990) and Willumsen et al. (1996). The higher range of reported EC t values have generally been associated with: (i) increases in fruit number with increasing salinity, presumably related to climatic conditions which likely contributed to excessive vegetative growth and poor fruit formation at low EC (Sonneveld and van der Burg, 1991), and/or (ii) little effect of salinity on fruit growth at low to moderate EC under conditions of low evaporative demand (Pearce et al., 1993b). Appreciable effects such as these were not observed in the present work. In the present study, EC t of yield was unaffected by climatic conditions. Similarly, Tüzel (2002), also working in Mediterranean conditions, obtained very similar EC t for different tomato crops grown in autumn or spring growing periods. The maintenance of similar EC t values, throughout the year, in the present work may be attributed to the maintenance of moderate evaporative demand during the cooler months in SE Spain. Evaporative demand appears to have been consistently above the level below which tomato fruit yield is unaffected by moderate salinity, as has been observed during cool periods in NW Europe. The decrease of marketable yield with increasing EC was affected by both cultivar and climate. Li (2000) also observed that reduced evaporative demand mitigated the negative effect of salinity on yield. It appears that under Mediterranean climatic conditions, climatic conditions can influence the degree of yield reduction associated with salinity, but that they do not influence EC threshold values. The yield decreases observed in the present study are similar to those obtained by Eltez et al. (2002) in Mediterranean climatic conditions, and are higher than those obtained in NW Europe (e.g. Sonneveld and Welles, 1988; Sonneveld and van der Burg, 1991; Li et al., 2001), presumably under conditions of lower evaporative demand. Both fruit weight and fruit number showed a threshold response and subsequent linear reduction to increasing salinity. The slope of the reduction of average marketable

1052 agricultural water management 95 (2008) 1041 1055 Fig. 6 Relationship between electrical conductivity of the drainage solution and the weight of fruits of different external appearance categories ( Extra, I and II ) expressed as the percentage of marketable fruit yield of each treatment in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates. Fig. 7 Relationship between electrical conductivity of the drainage solution and the soluble solids content, ph and titratable acidity of fruit expressed as the percentage of the values of treatment 1 in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). The straight lines show the best-fit linear regression. All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates.

agricultural water management 95 (2008) 1041 1055 1053 Fig. 8 Relationship between electrical conductivity of the drainage solution and estimated economic value of fruit yield expressed as percentages of the maximum value in each experiment (~, experiment 1; &, experiment 2; *, experiment 3; &, point eliminated from the linear regression of experiment 2). The straight lines show the best-fit linear regression (( ) experiment 1; (- - -) experiment 2; ( ) experiment 3). All values are the mean of four replicates and the bars represent the corresponding standard errors of the means of four replicates. fruit weight in the present study of 6.1% per ds m 1 was higher than the value of 3.5% per ds m 1 reported by Li et al. (2001) working in The Netherlands. This difference may be due to differences in evaporative demand. The effect of salinity on fruit weight, in the present study, was notably larger than that on fruit number. There are inconsistencies in the literature regarding the contribution of fruit number to EC-induced reductions in tomato fruit yield. Sonneveld and Welles (1988), Li et al. (2001) and Eltez et al. (2002) reported that the number of fruits was unaffected by moderate salinity, and that reduced yield was entirely due to smaller fruit. Our results are consistent with Adams and Ho (1989) and van Ieperen (1996) who observed that the number of harvested fruits per plant decreased with salinity, and was a contributing factor to reduced fruit yield. The decrease of fruit number in the present study was affected by EC and the duration of the harvesting period. The differences in fruit number were larger with increasing duration of the harvesting period as reported in other studies (Adams and Ho, 1989; van Ieperen, 1996). The reduction in fruit number observed in the present study appeared to be related to a reduction in the average number of flowers per truss and per plant observed with increasing salinity (Magán, 2005). This is consistent with the hypothesis of Cuartero and Fernández- Muñoz (1999) that stress restricts the number of flowers per truss. In the current work, increasing salinity increased the incidence of blossom-end rot, as has been commonly observed with tomato (e.g. Sonneveld and Welles, 1988; van Ieperen, 1996; Tüzel et al., 2001). The threshold response for BER observed in the present study has not been previously reported. The lack of discernible thresholds in other studies may reflect the limited number of EC treatments and relatively large EC differences between the lower range of salinity treatments. The incidence of BER with increasing salinity, particularly in experiment 2, may have been influenced by the use of sodium chloride to increase EC because of the antagonist effect of increasing sodium concentration on calcium uptake. There was a notable difference in susceptibility to BER between the two cultivars used in the present work, Boludo being more sensitive than Daniela. A number of studies have reported cultivar differences in the susceptibility to BER under saline conditions (Adams and Ho, 1992; Ho et al., 1995; Cuartero and Fernández-Muñoz, 1999). Cultivar differences in susceptibility to BER have been related to: (i) fruit growth rate (Ho et al., 1993), (ii) the efficiency of calcium (Ca) uptake and subsequent translocation of Ca to fruit (Adams and Ho, 1995), and (iii) Ca transport within the fruit (Adams and Ho, 1995). The higher incidence of BER in Boludo in the spring period compared to the autumn to spring period (Fig. 4) can be explained by a higher transpiration rate induced by higher evaporative demand increasing Ca transport to leaves which reduced Ca translocation to fruit (Adams and Holder, 1992). Additionally, higher spring temperatures promote faster fruit growth (Pearce et al., 1993a) which increases sensitivity to BER (Adams and Ho, 1993). Tüzel et al. (2001) reported a notably higher increase of BER with increasing salinity in tomato in a spring compared to an autumn growing period. The increase in tomato fruit quality with salinity in the present study has been consistently observed in other studies (e.g. Sonneveld and van der Burg, 1991; Cuartero and Fernández-Muñoz, 1999; Eltez et al., 2002). Fruit size was the only quality parameter negatively affected by increasing salinity. The other fruit quality parameters examined improved appreciably with increasing salinity. The percentage of category Extra fruits increased asymptotically with EC, in agreement with Adams (1989) and Adams and Ho (1989). The linear increases in total soluble solids content and titratable acidity, with increasing EC, was similar to those reported by Cornish (1992), Petersen et al. (1998), and Tüzel et al. (2001). Increases in total soluble solids content and titratable acidity enhance perceived fruit flavour (Grierson and Kader, 1986). While salinity generally enhances fruit quality, the reduction in fruit size can affect the price received by growers. The economic analysis conducted with the data from the present study indicated that the economic value of fruit yield decreased linearly with increasing salinity from an EC threshold for economic value of 3.3 ds m 1. This response was caused by the reductions in marketable fruit yield and fruit size, and occurred despite the improvement in visual fruit quality. The results of this study showed that increasing salinity of re-circulating nutrient solutions of tomato grown in soil-less system in SE Spain caused a notable improvement in fruit quality but that that improvement was unable to economically compensate for the reductions in marketable fruit yield and fruit size. While consumer markets for fresh tomato continue to value fruit size, and do not reward organoleptic quality, it is advisable for growers to maintain root zone EC at or below the suggested EC threshold value for fruit yield of 3.3 ds m 1. This conclusion has important

1054 agricultural water management 95 (2008) 1041 1055 practical implications for the management of re-circulation in SE Spain, where irrigation water, mostly obtained from aquifers, tends to have moderate levels of salinity. In general, the use of waters with an EC around 1 ds m 1 produces an excessive accumulation of salts in closed systems in the conditions of SE Spain (García and Urrestarazu, 1999). Consequently, it will generally be difficult to maintain the EC of re-circulating nutrient solutions at 3.3 ds m 1 in soilless growing systems with complete re-circulation. In the conditions of SE Spain, it appears that, generally, it will be necessary to use semi-closed re-circulation systems in which periodic discharge of part of the re-circulating nutrient solution is used to avoid EC increasing above the threshold where yield and income are reduced. The results of the present study suggest that semi-closed re-circulation systems may be an economically feasible form of re-circulating nutrient solutions, in SE Spanish conditions. In order to increase the effectiveness of re-circulation in this region, the collection and optimal use of rain water, and possibly the use of desalinated seawater, will be required to lower the salinity of irrigation water. This will reduce the rate of salinity increase and permit larger possible increases in EC during re-circulation before yield is negatively affected thereby prolonging the period of permissible salinity increase. An additional benefit would be reduced discharge of recirculating nutrient solutions and associated pollution. Acknowledgements We thank the research station of the Cajamar Foundation and FIAPA for funding and providing the facilities to undertake this work. 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