Fruit Yield of Tomato Cultivated on Media with Bicarbonate and Nitrate/Ammonium as the Nitrogen Source

ABSTRACT

This article presents the effects of nitrate/ammonium (NO₃ ⁻/NH₄ ⁺), applied at different proportions to the root media with or without 5 mmol bicarbonate (HCO₃ ⁻), on the yield and chemical composition of tomato fruit. Tomato plants were grown hydroponically (pH 6.9) in glasshouse conditions. The yield of fruit fresh matter from four clusters obtained from plants grown on the medium with NH₄ ⁺ was about 25% lower than from the plants grown on the medium containing NO₃ ⁻ as the nitrogen (N) source. Supplying NO₃ ⁻/NH₄ ⁺ at a ratio of 4:1 increased the fruit yield by about 20% in comparison with the value recorded for NO₃ ⁻−plants. The enrichment of the medium with HCO₃ ⁻ stimulated the bearing, while the result depended on the ratio of NO₃ ⁻/NH₄ ⁺. A combined treatment of HCO₃ ⁻ with NO₃ ⁻ or NH₄ ⁺ in the medium increased yields by about 28% and 11%, respectively, in comparison to plants cultivated without HCO₃ ⁻. The application of NO₃ ⁻/NH₄ ⁺ at ratios of 4:1 and 1:1 with HCO₃ ⁻ increased the respective yields by about 16% and 10% in comparison with plants grown without HCO₃ ⁻. Modifications in the composition of the media affected the accumulation of organic solutions in the fruit. The NH₄ ⁺ nutrition effected a 20% decrease in the accumulation of reducing sugars in the fruit in comparison to the fruit of plants grown in media with NO₃ ⁻. In the cultivation of plants in media with various NO₃ ⁻/NH₄ ⁺ proportions the intermediate values of the reduced sugar concentrations were recorded in comparison with the values obtained for NO₃ ⁻−plants and NH₄ ⁺−plants. The enrichment of media with HCO₃ ⁻ increased the concentration of sugars in fruit from about 28% (for NO₃ ⁻−plants) to about 10% (for NH₄ ⁺−plants).

Malate and citrate are the main constituents of carboxylates in tomato fruit. The form of nitrogen applied to the medium did not significantly affect the concentration of carboxylates in fruit. Significant differences in carboxylate concentrations appeared in fruit grown on media enriched with HCO₃ ⁻ ions. In comparison with the cultivation without HCO₃ ⁻, increases in the accumulation of carboxylates varied from about 22% to 30% depending on the form of the applied nitrogen. The concentration of amino acids in the fruit of plants grown with NH₄ ⁺ exceeded that in NO₃ ⁻−plants by about 55%. In the plants grown on media of modified NO₃ ⁻/NH₄ ⁺ proportions, the concentration of amino acids in fruits were positively correlated with the level of NH₄ ⁺ in the medium. The enrichment of media with HCO₃ ⁻ stimulated a further increase in amino acid concentration in fruit by about 9% in NO₃ ⁻ plants and about 21% in NH₄ ⁺ plants compared with the respective control (without HCO₃ ⁻).

Keywords:

• ammonium
• bicarbonate
• fruit yield
• nitrate
• tomato

ACKNOWLEDGMENTS

This work was supported by a grant from the KBN (PB 905/PO6/2001/20) to J. B.