The Effects of Intercropping Narrowleaf Lupine with Cereals under Variable Mineral Nitrogen Fertilization

Intercropping of legumes and cereals can bring many benefits to agriculture, including an increase in yield and the quality of the crops obtained. In addition, it is possible to reduce mineral fertilization, which can have a positive impact on the environment. The aim of the field research conducted in 2021–2023 in central Poland was to evaluate the yields obtained, the content and yield of total protein and the value of land equivalent ratio in the intercropping of narrowleaf lupine with cereals at different seeding levels of components and variable mineral nitrogen fertilization. The following factors were tested: 1—share of components in the sowing: narrowleaf lupine (NL) 120 seeds m⁻²; spring barley (SB) 300 seeds m⁻²; M1—NL 30 + SB 225 seeds m⁻²; M2—NL 60 + SB 150 seeds m⁻²; M3—NL 90 + SB 75 seeds m⁻²; spring triticale (ST) 450 seeds m⁻²; M4—NL 30 + ST 340 seeds m⁻²; M5—NL 60 + ST 225 seeds m⁻²; M6—NL 90 + ST 115 seeds m⁻² ; 2—mineral fertilization with nitrogen 0, 20, 40, 60 kg N ha⁻¹. The most favorable results were obtained with mixtures containing 60 + 150 seeds m² of narrowleaf lupine + spring barley and 90 + 115 seeds m^-2 of narrowleaf lupine + spring triticale. In addition, the favorable results and the lack of significant differences at fertilization of 40 and 60 kg N ha⁻¹ show the possibility of a limited dose of mineral nitrogen fertilization. Sowing narrowleaf lupine with spring barley at a ratio of 60 + 150 seeds m² or with spring triticale at a ratio of 90 + 115 seeds m^-2 and fertilizing with 40 kg N ha⁻¹ can be recommended for agricultural practice. The proposed management technique ensures high yields of good quality and thus can be an interesting solution for sustainable cultivation and be successfully implemented on farms.