## 4 Discussion
In the present study, the interaction of biofortification and variety (Table 1) for Zn content was very significant (\(p<0.0001\)). The Toma variety accumulated the highest amount of Zn in the Se_3 Zn_2 treatment (76.80 mg/kg), whereas the lowest Zn content was in the Korana variety in the Se_2 treatment (41.49 mg/kg). The interaction of biofortification and variety (Table 1) in Se content in the soybean grain was very significant (\(p<0.0001\)). The Ika variety at the Zn_2 treatment had the lowest Se content (26.77 mg/kg), whereas the highest Se content was found for the Suce variety at the Se_3 treatment (3601.37 mg/kg). It was interesting to find that the highest increment of Se content, compared to the control, was in the Ika variety, where Se content increased about 75 times at the Se_3 treatment. The interactions of variety and biofortification showedthe lowest increment of Se in the grain in comparison to the control for the Lucija and Toma varieties, whose increment was about 49 times compared to the control at the Se_3 treatment. Moreover, within the categorization of soybean genotypes over two years for the NUE of the soybean grain, the Korana variety had the highest NUE for Zn and Toma for Se. For vegetative mass, the highest NUE of Zn and Se were found for the Toma variety. These findings can be very valuable for the efficiency and sustainability of agricultural systems to increase NUE [80]. [PERSON] et al. [81] state that the cultivars Sonja and Lucija have different physiological responses to Se biofortification, where a higher dose of Se in biofortification decreases proline content in the Lucija variety and on the other hand effect negatively in the Sonja variety, where it is possible that it could act as pro-oxidant. The consumption of foods containing less than 0.1 mg Se kg\({}^{-1}\) results in selenium deficiency in the body, while the regular consumption of foods containing more than 1 mg Se kg\({}^{-1}\) is toxic [14]. Low concentrations of Zn and Se in the grain are mostly related to their low content in the soil system. In the present study, foliar biofortification greatly improved Zn and Se content in the soybean grain. According to [PERSON] [24], Zn-efficient plant genotypes have the ability to absorb higher doses of Zn may contain a higher dose of chelators, which bind the Zn and increase its physiological availability in the cells. [PERSON] et al. [82] investigated the effect of foliar fertilization with zinc (ZnSO\({}_{4}\cdot\)7H\({}_{2}\)O) on yield increase in four soybean cultivars (Lee, Forrest, Bragg, and Dodds) in New South Wales. Foliar Zn application in the stage before flowering led to an increase in yield in all four genotypes, the plants were taller, had a higher content of oil in the grain (in two varieties), and the zinc content in the leaves was increased and the phosphorus content was reduced. [PERSON] et al. [83] stated that the biodortification of Se and Zn in soybean was different among the elements in that the application of Se alone reduced Zn uptake. In contrast, the application of Zn promoted both Se and Zn in grains. [PERSON] et al. [84] reported that Se content in soybean grain was about three times greater with an application of MAP (-50% P\({}_{2}\)O\({}_{5}\)) + Se (rate of 80 g ha\({}^{-1}\)) fertilizer compared to phosphorus fertilizers without Se. In wheat (_Tritcium aestivum_ L.), [PERSON] et al. [85] also found a huge increment in Zn and Se with biofortification, Zn by 12.07-71.88% (up to 41.66-64.30 mg kg\({}^{-1}\)), and grain Se content by 131.81-527.21% (up to 0.21-0.50 mg kg\({}^{-1}\)). [PERSON] et al. [86] reported that in the production of Se-enriched food, a wider approach is needed through agronomic Se biofortification combined with breeding and molecular and biotechnology. The production of Se- and Zn-enriched soybean is especially important because soybean is one of the main and valued protein nutrients, not only for seed and flour but also for straw and dried green material [87; 88; 89; 90].