## 4 Discussion  
Nitrogen is an essential mineral for the plants to grow and produce high yield but is subjected to loss through nitrate leaching or denitrification. In Slovenian production technology, it is recommended to add nitrogen in small, required doses (100% RDN) at the beginning of strawberry vegetation and until the end of harvesting [9; 10]. In present research the content of other important minerals (P and K), organic matter and pH in the soil was at an optimal level and this is why the data presented in this paper confirm that probably N fertilisation had caused presented changes. We can see that fertilization with RDN had positive influence on total yield as it increased fruit number per plant without affecting the average fruit size. This is in accordance with the research of [PERSON] and [PERSON] [30]. A yield increase has been reported in several nitrogen-treated horticultural crops [31; 32]. [PERSON] and [PERSON] [32] reported in their study that fertilisation provided a regular and adequate supply of irrigation water and nutrients that could contribute to more incremental growth of strawberry plants. Similar results were also observed by [PERSON] et al. [33] and [PERSON] et al. [17] when they investigated the effects of different fertilisers on the yield and quality of strawberry fruit. While nitrogen fertilisation has been shown to have a positive effect on strawberry yield, the same cannot be said for calcium fertilisation. Our results are in accordance with [PERSON] et al. [34] who also could not prove any significant influence of calcium fertilisation on strawberry marketable fruit yield and berry weight. Only fertilisation with nitrogen (66% and 33% RDN) had a statistically significant impact on the content of sugars and organic acids in strawberries. Our results are in accordance with findings of [PERSON] and [PERSON] [32] research on strawberries who assumed, that this might be due to the increased synthesis of primary metabolites as there was more nutrients uptake and to their translocation to the fruits. While [PERSON] et al. [35] demonstrated, that chemical fertilizers produce the highest amount of nitrate in plant tissue, because of the direct release of nitrogen, plants requirements could be exceed when applied in higher doses (100% RDN). Calcium treated strawberries were firmer than those picked from the fertilised plants. Since calcium serves as an intermolecular binging agent that stabilizes pectin-protein complexes of the middle lamella, there was no surprise that we confirmed the findings of other researchers [34; 36]. Strawberries included in present study were the same variety; all fruits were harvested at the same maturity stage when fruits were fully red. As we monitored the colour parameters L*, a* and b*, we did not find any differences between fertilised and control fruits, which is similar to [PERSON] [37] findings. We confirmed these results with additional analyses of the anthocyanin content, showing the similarity in the content of major pigments in fruits. Strawberries fertilised with Lithovit had the highest sum of all identified phenolic compounds, due to maximum values of two major groups of phenolic compounds hydroxybenzoic and hydroxycinnamic acids. Many researchers confirmed significantly positive influence on the growth and chemical compositions such as carbohydrates and phenolic content in different various crops such as lettuce [38], tomato [39] and soybean [40]. Lithovit increased content of hydroxycinnamic acids and flavanols in comparison to control treatment, while strawberries from Ca-chelate treatment had lower phenolic content than from Lithovit treatment. In addition, nitrogen fertilization did not significantly change the phenolic profile with the exception of total flavanols. The typical aroma of strawberries comes not from just one or a few impactful aroma compounds, but from numerous volatiles present at certain concentrations and from the particular balance between them.