Productive behaviour of "cherry"-type tomato irrigated with saline water in relation to nitrogen fertilisation

Research on tomato tolerance to salt stress indicates that thresholds of ECe for the decrease of yield and plant growth are moderately high and differ among varieties. Some results suggest that nitrogen fertilisation may help increase the threshold for yield reduction. Most literature data have been collected either in small-scale containers or in the open field and both systems are often subjected to disturbances making hypotheses difficult to test. A set of experiments was conducted in large containers in a rainout-shelter field setting to assess the response of a "cherry"-type tomato variety to irrigation with saline water and to test the hypothesis that salt stress may be mitigated through nitrogen fertilisation. Tomato hybrid 'TOMITO F 1' was irrigated with water at four levels of salinity (0.7, 2.5, 5.0, and 10.0 dS m(-1) ECw) and three levels of nitrogen fertilisation (no added nitrogen = NO, 120 kg ha(-1) = N120, and 160 kg ha(-1) = N160) in factorial combination. Plant growth and water use were measured throughout the growth cycle, and gas exchange and leaf water potentials were measured at the fruit-growing stage. Two growing cycles were completed, one with high initial soil nitrogen (HN) and the second with low initial soil nitrogen (LN). No interaction was found between the application of nitrogen and plant response to saline irrigation. Plant growth and yield were affected by the saline treatments and less by nitrogen fertilisation, especially in the HN treatment. Irrigations with saline water resulted in increased values of soil salinity. Water use was lower with increasing soil and water EC, and the marginal reduction ranged from about 31 mm for each dS m(-1) of water EC at low salinity to about 6 mm for each dS m(-1) at high water EC. The marginal reduction in yield ranged from about 3.3 t ha(-1) for each dS m(-1) at low salinity water to less than 0.6 t ha(-1) for each dS m(-1) at high EC of irrigation water. Yield reductions were mainly due to lower fruit weight. Biomass values decreased as the salinity levels increased and fruit quality was improved in both cycles with increasing salinity. The hypothesis that nitrogen fertilisation could help tomato plants increase tolerance to salinity was not confirmed by data of this experiment and alterations induced by salinity in plant growth, yield and quality stabilised at high levels of water EC. (C) 2008 Elsevier B.V. All rights reserved.