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Composition of tomatoes and tomato products in antioxidants (WG1) page 45
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higher level of N fertilization, like yield and yield components, but in the same time the
percentage of soluble solids decreased (Merghany, 1997).
In conclusion it generally seems that nitrogen supply, especially at heavy rate, tends to
decrease the vitamin C content of tomato fruit and that it could be an indirect effect of
increased shading caused by a greater development of plant foliage favoured by high nitrogen
availability. The present tendency to reduce N supply in agriculture as much as possible for
objectives of food and environment quality and cost lowering would thus be favourable to
keeping high vitamin C content in tomato fruit.
Effect of Phosphorus
Increased P supply in hydroponics did not influence the vitamin C content of fruit
which yielded variations from 150 to 220 mg/kg (Saito and Kano, 1970). The effect of
phosphorus cannot be discussed because of the lack of studies. Further research would be
necessary.
Effect of Potassium
Very little was found about the specific effect of potassium on the tomato fruit vitamin
C content. Further research would be necessary.
Effect of Calcium
In a soil-pot culture experiment, Subbiah and Perumal (1990) tested the influence of
sources of calcium (calcium oxide, calcium chloride, calcium sulphate), concentrations (0.0%,
0.1%, 0.2% and 0.3% Ca), stages (S1 = 30th day after transplanting, S2 = 45th day after
transplanting, S3 = 60th day after transplanting), and number of sprays S1, S2, S3, S1+S2,
S1+S3, S1+S2+S3, S2+S3) on physico-chemical properties of tomato fruits, cv. Co.3. All the
pots received also 120 kg N/ha, 100 kg P2O5/ha and 100 kg K2O/ha. They could significantly
increase the ascorbic acid content (from 180 to 258, 268 and 265 mg/kg fresh matter) of the
tomato fruit by calcium sprays at 0.0, 0.1, 0.2 and 0.3% Ca concentration respectively. This is
in agreement with Bangerth (1976) and with a suggested hypothesis of a positive correlation
of Ca and vitamin C levels in tomato fruit presented in Table 20 (Premuzic et al, 1998).