Field evaluation of dual inoculation of alfalfa with Sinorhizobium meliloti and Penicillium bilaii

Field experiments were conducted at five sites to evaluate the effects of d ual inoculation of alfalfa (Medicago sativa L.) with Sinorhizobium meliloti and Penicillium bilaii, a phosphorus-solubilizing fungus, on the yield and quality of alfalfa hay. Dual inoculation with S. meliloti strain NRG-34 an d P. bilaii strain PB-50 increased nodule number and occupancy, but resulte d in only small increases in hay yield and total nitrogen and phosphorus co ncentrations of hay compared with inoculation with S. meliloti alone. There was little response of alfalfa to phosphorus fertilizer at the sites, and this may partly explain the small effects of dual inoculation of the two mi croorganisms. There were no significant differences in nodulation, hay yiel d or hay nutrient concentrations between alfalfa inoculated with separate N RG-34 and PB-50 inoculant products and that inoculated with a co-cultured i noculant. This similarity in response supports use of a single effective de livery system for the two different rhizosphere microorganisms, which is of great practical relevance as producers are more likely to adopt technology that requires a single inoculation procedure than one requiring two separa te inoculation procedures at planting time.