COMPARATIVE STUDY OF BIO- AND CHEMICAL FERTILIZATION IN STRAWBERRY PRODUCTION - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 130

plants show an increased demand mainly for nitrogen and potassium, which continues to rise
during the blossom and fruit-setting phases (Chepiñski et al., 2010). Potassium (K) is the
second essential macronutrient and the most abundantly absorbed cation that plays an
important role in the growth, metabolism and development of strawberry plants. However,
due to an imbalanced fertilizer application, potassium deficiency is becoming one of the
major constraints in plant production (Parmar and Sindhu, 2013). To overcome the problems
related to increasing utilization of synthetic nitrogen fertilizers, modern strawberry production
is based on the possibility of using some alternative methods, such as biofertilizations that
may enhance crop yields without adverse effects on soil properties and ensure basic criteria of
sustainable fruit production (Umar et al., 2009; Singh and Singh, 2009; Lütfi and Murat,
2009; Güneş et al., 2009; Pešaković et al., 2011; Pešaković et al., 2012; Pešaković et al.,
2013).
It is a well known fact that nutrient needs could be defined as those amounts necessary to
be absorbed to maximize plant performance. Within sustainable strawberry production this
performance cannot be identified only by vegetative growth, but also has to include yield and
nutritional fruit quality, as well as minimum or no risk of environmental pollution
(Agulbeiro-Santos, 2009). Considerations of the biofertilizer impact on nutrient
bioavailability in strawberry plants and particularly its contribution to yield-related
components have also received much attention and are important directions for future
research (Lütfi and Murat, 2009; Singh and Singh, 2009). In accordance with their findings,
yield increase due to biofertilizer application might be caused by the microorganisms'
production of plant hormone-like substances, such as indoleacetic acid, gibberellic acid,
cytokinins and ethylene.
Numerous studies have already shown that strawberries are a good source of natural
antioxidants (Anttonen et al., 2006; Capocasa et al., 2008; Milivojević et al., 2011). An
important question arising from the preliminary screening of antioxidant activity in
strawberry fruit concerns the polyphenolic profiles, i.e., which components within these
profiles contribute the most to differences in bioactive potential. These components are
mainly represented by flavonoids, phenolic acids and tannins, which play an important role in
controlling oxidative reactions in the human body and exhibit anticarcinogenic activities
(Määttä Riihinen et al., 2004; Milivojević et al., 2012b). Flavonoids are polyphenolic
phytochemicals that constitute a large group of secondary plant metabolites. Among them,
flavonols such as quercetin, kaempferol and myricetin, and their derivatives (primarily
glycosides) are considered the dominant flavonoids in strawberry fruit (Milivojević et al.,
2011).
Anthocyanins, the pigments responsible for the red color, also make an important
contribution to the total antioxidant activity of strawberry fruit (Cordenunsi et al., 2005).
Additionally, strawberries are known for a phenolic acid content (ellagic, gallic, p -coumaric
etc.) that constitutes about one-third of the dietary phenols. Ellagic acid, present in relatively
high levels in strawberries, has been suggested as a major phenolic acid providing
anticarcinogenic effects (Cordenunsi et al., 2005). Milivojević et al. (2011) noticed large
differences in the ellagic acid content between wild strawberry F. vesca and cultivated
varieties confirming that the content of each antioxidant may vary with genotype/cultivar.
Nutritional fruit quality is also affected by environmental conditions, cultivation techniques,