Inoculation of pea by application of Rhizobium in the planting furrow

Summary Selected streptomycin resistant strains ofRhizobium leguminosarum suspended in nutrient broth were added to the planting furrow immediately before the sowing of pea. The nodule occupancy by a strain isolated from Risø soil (Risø la) was increased from 74 to 90%, when the inoculum rate was increased from 3.7×10⁶ to 3.7×10⁸ cells per cm row. The experimental soil contained 10³ to 10⁴ cells ofR. leguminosarum per gram. An almost inefficient strain isolated from Risø soil (SV10) was less competitive with respect to nodulation on two pea cultivars than an efficient Risø strain (SV15) and an efficient non-Risø strain (R1045). The nodule occupancy by the introduced strains varied between pea cultivars.Irrespective of the generally high nodulation by the efficient strains introduced to the soil, the pea seed yield, compared to pea nodulated by the indigenous population, was not significantly increased. Neither were two commercial inoculants, applied in rates corresponding to 3 times the recommended rate, able to increase the yield. This suggests that the indigenous populations ofR. leguminosarum were sufficient in number and nitrogen fixing capacity to ensure an optimal pea crop. However, some inoculation treatments slightly increased the seed N concentration and total N accumulation, indicating that it may be possible to select or develop bacterial strains that may increase the yield.