Comparison of crop yield, soil microbial C, N and P, N-fixation, nodulation and mycorrhizal infection in inoculated and non-inoculated sorghum and chickpea crops

Abstract

A field experiment was conducted on a clay loam soil to assess the response of crops to inoculation and inorganic and organic fertilizers. Microbial biomass C, N and P under sorghum ( Sorghum bicolor L.) and chickpea ( Cicer arietinum L.) were significantly higher ( r=0.641–0.735, P<0.01) when a combination of Azospirillum brasilense or Rhizobium, Bacillus megaterium and Glomus fasciculatum were used, and was maximum with 50% recommended fertilizers (40 kg N ha −1 and 8.73 kg P ha −1 for sorghum; 10 kg N ha −1 and 8.73 kg P ha −1 for chickpea) along with bioinoculants. Biomass C, N and P in the rhizosphere soil of sorghum–chickpea sequences were greater after 30 days and decreased subsequently (at 60 days or at harvest). A strong correlation ( P<0.01) of biomass C, N and P was observed with N and P uptake of sorghum and chickpea indicating the role of microorganisms in crop response. Azospirillum population in the rhizosphere improved significantly from 38.0 cfu g −1 under recommended fertilizer to 176.8 cfu g −1 under farm yard manure (FYM) and bioinoculants. Nodule dry weight and acetylene reduction activity (ARA) were significantly higher in the treatments receiving Rhizobium inoculation. Vesicular arbuscular mycorrhizal (VAM) infectivity was also improved significantly with combined inoculants and FYM compared to sole application of FYM or fertilizers (N and P). Application of fertilizer nutrients along with FYM, use of nitrogen fixers, phosphate solubilizers and VAM significantly increased grain ( r=0.618, P<0.05) and straw yields ( r=0.602, P<0.05) and, in general, decreased C:N and C:P ratio. The results suggested that for maximum crop yield only 50% of the required fertilizer might be supplied along with bioinoculants.