Rhizobium inoculation in forage legumes intercropped with cereal for ruminant feeding

Intercropping is an agroecological practice that combines two or more crops simultaneously in the same field. This is particularly beneficial when cereals like wheat are combined with forage legumes, mainly under organic farming systems. Forage legumes play a vital role in sustainable agriculture by supporting livestock production and enhancing biological nitrogen fixation (BNF). BNF efficiency depends on the compatibility between legume species and their rhizobial strains. Applying exogenous rhizobial inoculants can enhance BNF and legume performance, especially in fields with limited legume cultivation history. Here the intercropping (IC) of durum wheat (Triticum turgidum subsp. durum) with three forage legumes (Trifolium subterraneum, Medicago polymorpha, and Vicia sativa) compared to wheat monocropping was evaluated. Crops were grown under two levels of N-fertilizer (60 and 120 kg ha-1) with and without species-specific rhizobial inoculants (Visjon Exceed, USA). The field trial was conducted on an organic farm in Patti, Messina (38°11’N, 14°99’E, Italy) to improve wheat productivity and forage quality from wheat byproducts. The chemical composition of feed samples, in terms of protein and fibrous fractions, was determined using standard analytical methods. The three-way ANOVA (at P≤0.05) revealed significant effects of N-fertilization (P=0.007), rhizobial inoculation (P=0.009), and legume IC (P≤0.001) on wheat grain yield. While N-fertilization positively influenced weed biomass (P=0.026), legume IC reduced it (P≤0.001). Wheat straw yield decreased with legume IC (P=0.015; 3.8 Mg ha-1 in the control and 2.5 Mg ha-1 with M. polymorpha), but among legume species, V. sativa produced the highest additional forage yield (1.17 Mg ha-1), outperforming T. subterraneum and M. polymorpha (0.61 and 0.49 Mg ha-1). Rhizobial inoculation significantly increased legume yields than non-inoculated crops (0.64 vs. 0.50 Mg ha-1). Additionally, rhizobial inoculants and Nfertilization (P=0.004 and P=0.001) enhanced the protein content of forage legumes (10.4 vs 9.3%, and 10.5 vs 9.2%, respectively), without significantly (P>0.05) affecting the fibrous fractions (NDF, ADF, ADL), thus contributing to the improvement of the quality of wheat straw. These findings confirm the benefits of IC in enhancing cash crop productivity and improving the quality of forage for ruminant feeding in organic, cereal-based cropping systems. This work was supported in part by the Italian Ministry of Foreign Affairs and International Cooperation, grant number US23GR18 (RE-FARM project, CUP: J43C23000110001).