Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2004
Publication Date: 12/1/2004
Citation: Ben-Oliel, G., Kant, S., Naim, M., Rabinowitch, H., Takeoka, G.R., Buttery, R.G., Kafkafi, U. 2004. Effects of Ammonium to Nitrate Ratio and Salinity on Yield and Fruit Quality of Large and Small Tomato Fruit Hybrids. Journal of Plant Nutrition. 2004. Vol 27, No. 10. p. 1795-1812. Interpretive Summary: Tomato is one of the most important greenhouse vegetables in semi-arid regions, where soil and groundwater salinity are pre-dominant. Under intensive fertigation, nitrogen not only affects plant growth, it may also alter the salinity tolerance of plants depending on its ionic form. Saline conditions markedly improve tomato and other fruit quality components due to reduction in water accumulation in the pericarp, and the consequent increase in sugar and acid concentrations. However, fruit yield is usually lower under salinity than in control. There is evidence that under saline condition, some fertilization regimes result in higher yields than others. The objective of this study was to determine the combined and/or sole effects of NO3- and NH4+ under saline conditions on quality and yield of tomato genotypes with different fruit sizes, yields and fruit flavors, under protected growing conditions. Our results suggest three possible ways of counteracting the adverse effects of salinity in hydroponically grown tomato: (1) the use of mainly NO3- with the addition of up to 1 mM NH4+ improves fruit size with minimal loss of fruit quality; (2) the use of small fruit cultivars which are less susceptible to salinity up to 45 mM NaCl, and (3) the use of mild saline conditions of 20 mM NaCl in the nutrient solution which hardly reduces yield but significantly improves fruit quality.
Technical Abstract: Tomato cultivars respond differently to nitrogen sources and to saline conditions, in terms of both yield and fruit quality. Interactions between salinity and NH4+/NO3- ratios with tomato genotypes were studied. The effect of four ammonium levels (0, 1, 2, 4 mM of total 8 mM N) and two salinity levels (0 and 45 mM NaCl) on R 144, and the effect of two salinity levels (0 and 45 mM NaCl) on four tomato hybrids (R 144, R 175, FA-612, and FA-624) were studied in two greenhouse experiments. The effects of two NH4+ levels, (0 and 2 mM out of total N at 8 mM), and two salinity levels (0 and 20 mM NaCl) on large-fruited (R 144) and small-fruited (FA-612) tomato hybrids were also studied in a nethouse. The NaCl at 45 mM resulted in a smaller leaf area index (LAI), lower plant dry matter and lower fruit yield than controls. Addition of 1 mM NH4+ to the nutrient saline solution contributed to improved growth. Genotypes bearing large fruits were more prone to suffer yield losses under saline conditions than those having small fruit. In the second experiment, salinity treatment resulted in improved fruit total soluble solids (TSS), electrical conductivity (EC) and titratable acidity in all of the hybrids except for FA-612. Fruit TSS was inversely correlated with yield. However, the ratio of TSS decline versus yield varied among the hybrids. At mild salinity (20 mM NaCl), fruit TSS and titratable acidity were significantly increased in R 144 while yield was slightly decreased. Transpiration rate decreased with the presence of ammonium in the nutrient solution in both hybrids. The highest and lowest values were obtained for FA-612 and R 144, respectively. The detrimental effect of higher salinity is mainly attributed to the decrease in LAI and subsequent reduction in water uptake, resulting in low fruit weight. Addition of 1 mM ammonium to 7 mM nitrate in the nutrient solution had an ameliorating effect on tomato fruit yield under high saline conditions.