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 dual 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 and P. bilaii strain PB-50 increased nodule number and occupancy, but resulted in only small increases in hay yield and total nitrogen and phosphorus concentrations 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 microorganisms. There were no significant differences in nodulation, hay yield or hay nutrient concentrations between alfalfa inoculated with separate NRG-34 and PB-50 inoculant products and that inoculated with a co-cultured inoculant. This similarity in response supports use of a single effective delivery 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 separate inoculation procedures at planting time. Key words: Co-cultured inoculant, Medicago sativa, phosphorus-solubilizing microorganisms, Penicillium bilaii, Sinorhizobium meliloti