Effects of constant and fluctuating salinity on the yield, quality and calcium status of tomatoes

SummaryTomato plants were grown in nutrient film (NFT) at constant salinities of 3, 5.5 and 8 mS cm−1 and also with the salinity fluctuating from 8 mS cm−1 during the day to 3 mS cm−1 at night (the 8/3 mS treatment). The yield was always depressed at 8 mS cm−1. During the first four weeks of harvesting this was mainly due to reduced fruit size, but later fruit number also decreased. The 8/3 mS treatment reduced fruit size and number more than a constant 5.5 mS cm−1 (the average of the fluctuating salinities), suggesting that 8 mS cm−1 affected the long-term development of the plants. Increasing the salinity by addition of either major nutrients (K, Mg, Ca and NO3–N) or NaCl gave similar responses. The sugar and acid contents of the fruit juices increased with salinity but these responses disappeared when the data were expressed on a dry matter basis. This lack of response to salinity was confirmed by the sugar analyses of fruit after freeze-drying. Increasing the salinity with NaCl depressed the K content of the dry matter but increased the Na content; both responses were greater with the 8/3 mS treatment than at a constant 5.5 mS cm−1. The depression in the Ca content of the fruit was more marked in the later trusses and in the distal tissues of the fruit. This decrease was more severe with the 8/3 mS treatment than with a constant 5.5 mS cm−1, thus supporting the notion of a long-term effect of salinity on xylem development. The fluctuating salinity did not, therefore, appear to have any advantage over a constant one.