The Grain Protein Content of Polish Cereals Other than Wheat: Can It Be Increased by Combining a Crop Sequence System, Cultivar Selection, and Plant Protection?

After legumes, cereals are the most important source of protein for humans and livestock worldwide. One way to meet growing nutritional demands is to increase the grain protein content (GPC) of cereals. Breeding advances in this regard should be supported by optimized agricultural practices. The GPCs of winter rye, winter triticale, spring barley, and spring oats grown in 2018–2022 in northeast Poland were evaluated to determine the influence of the crop sequence system (continuous monocropping, crop rotation), cultivar (two for each species), plant protection level (control treatment, herbicide, herbicide, and fungicide), and interactions among these factors. The cultivar selection was a significant GPC determinant in all cereals. Growing triticale in crop rotation after a legume increased its GPC compared to continuous monocropping, but decreased the GPC of rye and had no effect on the GPCs of spring cereal that followed non-legume crops. Using herbicides and herbicides combined with fungicides promoted the GPC of rye and oats, but not of triticale and barley. The heterogeneity of the interaction effects of the studied agricultural practices on the GPCs of the individual cereals prevents the identification of a universal combination that would ensure the highest GPC levels. The inter-annual weather variability played a significant role in shaping the GPCs of cereals and in modifying the influence of the controlled factors.