Response to salinity of a tomato crop in Mediterranean climate conditions

In Mediterranean regions, high quality water is not commonly available for irrigation. For closed soilless growing systems, initial water quality affects the management of the recirculating solution. This study was conducted to obtain criteria for determining when to flush out recirculating solution in closed systems used for tomato production. During a spring growing season, seven levels of nutrient solution salinity (2.5 - the control, 3, 4, 5, 6, 7 and 8 dS m(-1)) were compared on long life tomato (cv. Daniela). The different salinity levels beyond the control were obtained by the addition of sodium chloride. The experiment was conducted in Almeria, Spain. Total and marketable fresh yield, size distribution, visual imperfections, dry matter content, soluble sugar content, and acidity were measured. After a threshold value of 3.85 dS m(-1), fresh weight decreased 9.1% per dS m(-1). Salinity negatively influenced fresh weight and marketable fruit number. The values of several quality parameters tended to increase with salinity. The percentage of class 'extra' fruits (highest visual quality) increased progressively with salinity until 5 dS m(-1), after which there was no consistent increase. Fruit soluble sugar content and acidity increased linearly. The increase of blossom-end rot with salinity was compensated by a large decrease in blotchy ripening. Fruit dry matter percentage increased linearly, but both the marketable dry matter yield and dry weight per marketable fruit tended to decrease above 5 dS m(-1).