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Composition of tomatoes and tomato products in antioxidants (WG1) page 56
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idea of the nutrient stock, total or "available" but not of the soil feeding capacity (Dumas,
1990). Indeed for nitrate there is a great variability within time and space according to
environmental conditions (mineralisation, reorganisation, leaching). For P and K it has been
shown that tomato roots could have a very high extraction capacity : 80% of P or K absorbed
by plants can come from the soil P or K part which was not given as "available" by chemical
analysis (Maertens and Bosc, 1988). Interactions exist between ions (antagonism between
potassium and calcium-magnesium, or synergism nitrogen-phosphorus). Buffering properties
of soils often moderate nutrient relations. Fertilization must be related to the whole crop
management . It is an evidence that fertilization practice and efficiency are most dependent on
irrigation mode for instance. But it also depends on soil structure and rooting conditions.
Indeed P uptake has been found to be proportional to root surface area and K is above all
absorbed by young parts of growing roots. Fertilization has to be reasoned according to the
situations.
Various growth and development regulators seem to positively influence the tomato
fruit content in carotenes and vitamin C. But before planning to apply such substances to
processing tomato fields, studies should be undertaken about the feasibility of such
interventions in open field, about possible consequences of applications on the crop response
and about possible modifications of fruit quality (other properties, residues?).
As a result of the present literature review it appears very difficult and hazardous to
define optimal growing conditions which would enable farmers to maximise the biosynthesis
and the storage of lycopene, vitamin C, vitamin E and phenolic compounds in the tomato fruit
during ripening. These issues have not been much addressed. It might be of great interest to
understand better the effects of light and temperature -influenced themselves by water
relations, mineral nutrition and cultural techniques like the date of crop installation and plant
spatial distribution, which alter the crop canopy structure- on the concentrations of these
compounds in different cultivars or genotypes during the fruiting period.