Biomass Yield, Nitrogen Content and Uptake, And Nutritive Value of Alfalfa Co-Inoculated with Plant-Growth Promoting Bacteria

Alfalfa (Medicago sativa L.) has high forage yield potential, protein quality, palatability, and digestibility, and low seasonality. The aim of this study was to evaluate the effects of strains of Sinorhizobium meliloti and Azospirillum brasilense on the nutritive content, bromatological composition (crude protein [CP], neutral detergent fiber [NDF], acid detergent fiber [ADF], and in vitro digestibility of dry weight [IVDDW]), and shoot dry weight (SDW), relative chlorophyll index (RCI), number of tillers (NT), plant height (PH), and root dry weight (RDW) and volume (RV), of alfalfa grown in a Typic Ultisol. The experiment consisted of eight combinations of plant-growth promoting bacteria (PGPB). The treatments were as follows: T1:non-inoculated control without N-fertilizer (NI); T2: NI + N-fertilizer, and inoculated with T3: Sinorhizobium (=Ensifer) meliloti SEMIA 116 + N-fertilizer; T4: S. meliloti SEMIA 116 + A. brasilense Ab-V5 + Ab-V6 + N-fertilizer; T5: S. meliloti SEMIA 134 + N-fertilizer; T6: S. meliloti SEMIA 134 + co-inoculation + N-fertilizer; T7: S. meliloti SEMIA 135 + N-fertilizer; and T8: S. meliloti SEMIA 135 + co-inoculation + N-fertilizer. S. meliloti strains are used in commercial inoculants for the alfalfa, and A. brasilense for several non-legumes and legumes in Brazil. The experiment was performed for three successive cuts under greenhouse conditions. Application of N-fertilization increases the production cost, making alfalfa cultivation unviable. Inoculation with three strains of Sinorhizobium meliloti highly promoted alfalfa growth, considering several parameters, including PH, RCI, NT, SDW and RDW, nutritive value, and with an emphasis on RV, and total N content and total N accumulated in shoots and roots. No further increases were observed with the co-inoculation with the PGPB A. brasilense. Studies in field and greenhouse conditions are necessary to verify the benefits of the use of PGPB in the cultivation of alfalfa