## 4 Conclusions  
In conclusion, it is important to highlight the complex interactions between genotype, nitrogen fertilization, phytochemical composition, and mycotoxin contamination in barley, emphasizing the need for integrated breeding and crop management strategies to optimize yield, grain quality, and safety. Our research showed that genetic factors are the primary determinants of grain yield, with hybrid varieties (mainly Hobbit and Zoom) yielding better than the conventional one (Sandra). Nitrogen fertilization significantly impacted certain flavonoid contents, particularly in hybrids, but had little effect on overall yield. Mycotoxin accumulation (mainly DON and 15-Ac-DON) in grains varied by barley variety, with Sandra showing the least susceptibility, while Hobbit, Zoom, and Galation contained mycotoxins regardless of nitrogen levels. Higher contents of antioxidant compounds in barley may correlate with reduced mycotoxin levels, although this relationship is complex. Optimal nitrogen management is essential to increase yields and phenolic concentrations while minimizing the risk of mycotoxin contamination of the grain. Therefore, breeding should aim to combine high yields with resistance to mycotoxins and favorable phytochemical profiles to enhance both productivity and grain quality and safety. The current study, although showing some important limitations, provides a significant insight into future research focused on determining the impact of different rates of nitrogen fertilizers and barley varieties, not only on yield, but also on important quality and safety characteristics of barley grain. The research was conducted in specific regions of Poland, which may not represent barley growing conditions in other countries or climates. Therefore, the results may not be universally applicable. Moreover, only four winter barley varieties were examined (Hobbit, Zoom, Galation, and Sandra). The findings may not  
Figure 4: [PERSON]’s correlation between the concentrations of bioactive compounds (phenolic acids, flavonoids and carotenoids), mycotoxins identified in barley samples, fertilization doses, and yield. Color (red/blue) and color intensity indicate the direction and the strength of the association. Green signs reflect statistical significance of the correlation at the level of \(p<0.05\) (*), \(p<0.01\) (**), and \(p<0.001\) (***); 15-acetyldeoxynivalenol (15-AcDON), deoxynivalenol (DON). reflect the performance of other barley varieties that could exhibit different responses to nitrogen fertilization and mycotoxin contamination. Additionally, this study investigated only a limited range of nitrogen fertilization levels. Future research could explore a broader range and more specific N application rates to determine the optimal conditions for maximizing yield and grain quality and minimizing mycotoxin contamination risk. Results may vary across different years due to variations in weather patterns, pest pressures, and soil health, which can affect plant growth and mycotoxin levels. By addressing these limitations in future research, the understanding of how cultivation practices and environmental variables influence the quality and safety of barley could be further enhanced. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15126904/s1](https://www.mdpi.com/article/10.3390/app15126904/s1)]([https://www.mdpi.com/article/10.3390/app15126904/s1](https://www.mdpi.com/article/10.3390/app15126904/s1)). Figures S1 and S2: Chromatograms showing retention times for the polyphenols identified in barley grains; Figures S3 and S4: Chromatogram showing retention times for the carotenoids identified in barley grains; Figure S5: Standard calibration curves for fourteen analyzed mycotoxins; Figure S6: LC-MS/MS example chromatograms of mycotoxin solutions versus representative barley samples contaminated by mycotoxins. Conceptualization, R.K., D.S.-T., D.L., and B.G. ; data curation, R.K., D.S.-T., K.K., E.H., and A.N.