Co-inoculation of Resident AM Fungi and Soybean Rhizobia Enhanced Nodulation, Yield, Soil Biological Parameters and Saved Fertilizer Inputs in Vertisols under Microcosm and Field Conditions

Abstract

Interaction effect of native AMF (arbuscular mycorrhizal fungi) and root nodulating soybean rhizobia was evaluated on soybean growth and associated soil biological parameters under microcosm (sterilized and un-sterilized) and field conditions. Treatments under microcosm experiment consisted of two rhizobial strains Bradyrhizobium japonicum (5a) and Bradyrhizobium liaoningense (17c) and one AMF (mixed culture of Glomus intraradices, G. mosseae and G. geosporum) alone and in combination with 50 per cent of recommended dose of NPK fertilizers (20:26.2:16.6 kg N:P:K/ha) and control. For field trial, only B. japonicum (5a) was included with AMF and fertilizers. Under both the conditions, bradyrhizobial and AMF inoculation at 50 per cent RDF produced significantly higher nodules, nodule dry weight and grain yield when compared to control plants and was found to be comparable with plants grown with RDF. The two-way ANOVA analysis revealed that interaction effect of soil conditions and inoculation treatment was significant on nodulation and yield. Irrespective of soil conditions, co-inoculation of AMF and Bradyrhizobium with or without 50 per cent RDF produced comparatively higher nodulation, N uptake, had higher AM colonization and grain yield than other treatment combinations and was found significantly higher over control plants. It means Bradyrhizobium inoculation is favoring AMF colonization. AMF spore density in soil and per cent root length colonized by AMF and the background population enhanced in presence of Bradyrhizobium both under microcosm and field evaluation. Soil enzymes activities of AMF and Bradyrhizobium inoculated samples had higher alkaline and acid phosphatase activity over other treatments. Inoculation of AMF alone and Bradyrhizobium with 50 per cent showed higher activity of acid and alkaline phosphatases indicating the release of P from organic pool. Moreover, inoculation of AMF either used singly or in combination also enhanced ß- glucosidase and fluorescein diacetate (FDA). Overall, higher soil enzymes particularly alkaline phosphatases in AM-mediated rhizosphere of Bradyrhizobium and 50 per cent RDF combination was found to be efficient in producing higher yield and N uptake at reduced dose of NPK fertilizers.