International Journal of Plant & Soil Science

Nitrogen fixation by legume-rhizobium symbiosis is important to agricultural productivity and is therefore of great economic interest. The effect of mono and co-inoculation with Rhizobium and PGPR was investigated in two consecutive years during 2010-11 and 2011-12 in Vertisols of central India on soybean. Soybean crop was grown during rainy season of 2010-11 with mono-inoculation of Rhizobium (10 isolates) and PGPR (15 isolates). During 2011-12 previously screened 3 taxonomically confirmed isolates each of Rhizobium and PGPR as mono-inoculation and their combinations as co-inoculation along with fertilized uninoculated control (FUI) and unfertilized uninoculated control (UFUI) were also evaluated. The treatments were laid out in RCBD with three and four replications respectively. The effects of mono-inoculation and co-inoculation on soybean were observed on soil properties, nodulation, yield, total nutrients (NPK) uptake by crop, harvest index, nitrogen harvest index and additional BNF (biological nitrogen fixation). Seed inoculation either mono or co-inoculation improved the status of post harvest soil nutrients as compared to initial status, UFUI and FUI. During 2010-11 the total soil N in post harvest soil sample was maximum with one of the rhizobial isolates (441 mg kg^-1 soil) while in FUI it was 402 mg kg^-1 soil while with PGPR isolates it was 439 and 401 mg kg^-1 soil respectively. Next year it was 432 and 430 mg kg^-1 soil respectively in co-inoculation and FUI.

Mono-inoculation promoted germination, nodulation, seed yield, harvest index, nitrogen harvest index and additional BNF significantly over FUI but co-inoculation was found more synergistic. Significantly correlations were observed between oven dried weight of nodules with straw and seed yields and total N uptake by crop.