THE EFFECT OF BRADYRHIZOBIUM STRAINS ON MONOCROPPED AND INTERCROPPED SOYBEAN (GLYCINE-MAX L. MERR.) BIOMASS AND PROTEIN

Intercropping soybeans with corn can produce yields of silage comparab le to monocrops of corn but with a higher protein concentration. To ma ximize N-2-fixation by soybeans, it is important to use a strain of br adyrhizobium that is well adapted to local soil and climate conditions . In 1991 and 1992 an experiment was conducted in Truro, Nova Scotia, Canada, to compare a locally isolated bradyrhizobium strain, NS1, with a commercial strain (COM). Corn-soybean intercrops and soybean monocr ops were grown and various response variables were measured to assess the efficacy of each strain. NS1 proved to be superior to the commerci al strain of bradyrhizobium in both intercrops and monocrops when soyb ean plant protein concentration, soybean seed protein concentration an d soybean seed biomass yield were measured. For intercrop protein yiel d and intercrop protein concentration NS1 outperformed COM only in mon ocrops, Protein yields per hectare of soybeans grown in either system were higher when NS1 was used as an inoculant. No differences were obs erved between inoculants in biomass yields of soybeans grown in either system. Since soybeans only contributed 28.5% to the total biomass of intercrops, the biomass of the corn probably masked the differences b etween the two inoculants for intercrop protein yield and concentratio n. However, even under the stressful conditions for soybean plants ass ociated with intercropping, soybean protein concentrations and yields when grown in intercrops were higher for the NS1 strain of bradyrhizob ium. It appears that selection of a locally adapted strain of inoculan t for soybeans can prove useful in both monocropping and intercropping systems.