Agriculture Reference
In-Depth Information
was observed [53]. Systematic fertilization with pig and poultry manure can lead to the
accumulation of heavy metals, especially copper.
We found the growing method to have no influence on cadmium (0.0027 mg 100g
-1)
and cobalt
(0.007 mg 100g
-1
) levels in all cultivars. In the present study, the detected levels of contaminants
were found to be markedly lower than the maximum limits allowed by Law: 100 μg kg
-1
for
Pb and 50 μg kg
-1
for Cd (EU Regulation 1881/2006).
The concentrations of heavy metals in tomato fruit decreased in the order of
Zn>Pb>Cu>Cr>Ni>Co>Cd.
10. Nitrate content
Nitrate content of vegetables depends on a number of external and internal factors [76; 77].
From external factors should be mentioned; supply of substrate with nitrate, light, time of day,
temperature, season, supply with water, relative humidity, carbon dioxide concentration in
the air, supply with biogenic elements, the influence of the accompanying cations, heavy
metals, herbicides, chemical properties of the soil, location, time of sowing, time and method
of harvest, storage conditions, etc. [78; 79]. Among the internal factors, the most important are
the genetic specificity in the accumulation of nitrate (differences between species and differ‐
ences within genotypes), the distribution of nitrate in certain parts of the plant and the age of
the plants..
Nitrate content of various parts of a plant differs [76]. Vegetables that are consumed with their
roots, stems and leaves have a high nitrate accumulation (up to 2000 mg kg
-1
), whereas those
with only fruits and melons as consumable parts have a low nitrate accumulation [80]. The
tomato belongs to the vegetable plants which accumulate less nitrates than other vegetables
(100 to 150 mg kg
-1
). The effect of climate on nitrate accumulation has been studied [81], and
it was found that nitrate content was lower in years that had a high rainfall. In warm and wet
years, increased accumulation of nitrate is possible, regardless of whether the nitrogen
originates from organic or mineral sources [82]. A comparable study performed in Austria on
17 vegetables found lower nitrate contents (-40% to -86%) in organic vegetables, with spinach
being an exception [84]. In Germany, a comparison on carrots showed 61% less nitrates in
organic ones [85]. In contrast, two other studies performed on tomato in Israel [83] and carrot
in Norway did not show noticeable differences [86].
Nitrogen-rich organic fertilizers can also generate lower nitrate contents, but when minerali‐
zation conditions are very favorable they can also lead to high nitrate accumulations [87]. The
use of organic fertilization with slowly or moderately available nitrogen (especially composts)
is key to explaining the generally observed lower nitrate accumulation in organic vegetables
[88].
Differences in nitrate content between cultivars in organic production are present. The lowest
nitrate concentration was observed in 'Elpida' (20 mg kg
-1
) and it was statistically significantly
(p<0.05) lower than the nitrate content in the 'Robin' and 'Amati' cultivars. The differences in
