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

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 south-eastern 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 (ECt). There were only small effects of climate and cultivar on the ECt 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 ECt 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 ECt of 3.0 dS m-1 for marketable fruits. Reduction in fruit number with salinity made a smaller relative contribution to reduced yield. Blossom-end 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 marketable yield. In the economic analysis, the value of increased visual fruit quality was offset by reduced yield and smaller fruit size.