Co-inoculation dose and root zone temperature for plant growth promoting rhizobacteria on soybean [Glycine max (L.) Merr] grown in soil-less media

Inoculation dose affects the efficacy of bacterial inoculants applied in agriculture. Effects of the co-inoculation dose of two plant growth promoting rhizobacteria (PGPR) strains, Serratia proteamaculans 1-102 and S. liquefaciens 2-68, with Bradyrhizobium japonicum on soybean [Glycine max (L.) Merr.] growth, nodulation and nitrogen fixation were investigated under controlled root zone temperatures (RZTs; 25, 20 and 15 °C) in soil-less media. The results showed that the effective dose range for both PGPR strains is 107–109 and their optimal co-inoculation dose was 1×108 cells per seedling. This was not affected by RZT. The co-inoculation of PGPR at their optimal dose increased nodule number, plant dry weight and fixed nitrogen. Nitrogen fixation efficiency was also improved by the co-inoculations. Use of nodulation dynamic linear models made the quantitative description of the nodulation process possible. The calculated dynamic parameters revealed that PGPR co-inoculation shortened the nodule initiation time and increased the nodulation rate.