**5. Conclusions**

The grain yield differentiations of cereal mixture variants was different than protein and metabolic energy yield due to the lower grain yield but higher content of protein and metabolic energy in the grains of naked forms of barley, oats, and wheat.

A higher grain yield was indicated from a mixture of cove forms of spring barley and oats. However, the yield of protein and metabolic energy of mixtures with the share of naked forms of barley, oats, and wheat was similar to that of covered forms.

Regardless of the soil quality and sowing density, the highest grain yields were obtained from a two-mixture component of covered barley with covered oats (Albic Luvisols: 6.3 t ha−<sup>1</sup> and 6.0 t ha −1, Haplic Arenosols: 5.08 t ha−<sup>1</sup> and 5.09 t ha −1, respectively). Three mixture components (CB + CO + W) lack of differentiations of cereal mixture variants in terms of yield and protein yields was noted.

**Author Contributions:** Conceptualization, D.L. and A.K.-K.; methodology, D.L.; software, A.K.-K.; validation, D.L., A.K.-K. and K.P.; formal analysis, A.K.-K.; investigation, D.L.; resources, D.L.; data curation, D.L.; writing—original draft preparation, A.K.-K., D.L., K.P.; writing—review and editing, A.K.-K., D.L., K.P.; visualization, A.K.-K.; supervision, D.L.; project administration, D.L.; funding acquisition, D.L. and K.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Institute of Soil Science and Plant Cultivation, State Research Institute in Puławy, Poland and was funded by University of Life Sciences in Lublin, Poland.

**Acknowledgments:** We would like to thank Kazimierz Noworolnik, who is an employee of the Department of Cereal Crop Production, the Institute of Soil Science and Plant Cultivation—the State Research Institute in Puławy, Poland for his contribution to the creation of scientific work and for long-term collaboration.

**Conflicts of Interest:** The authors declare no conflict of interest.
