Effect of plant growth promoting bacterium (Azospirillum brasilense) and Bradyrhizobium on growth, yield and nitrogen fixation of groundnut (Arachis hypogaea L.)

Pot and field experiments were conducted to investigate the effect of biofertilizers on growth, yield and symbiotic properties of groundnut. Azospirillum brasilense, which was isolated from Gezira Research Station soil, was used as a plant growth promoting Rhizobacterium (PGPR). Groundnut variety Medani was inoculated with Bradyrizobium and/or Azospirillum and grown in pot and field at the Gezira research station farm in mid June, seasons 2000 and 2001.15N methodology was used to calculate the nitrogen fixed by groundnut using a non-nodulating groundnut isoline as the reference crop. Plant tissue analysis from the pot experiment was done to determine the 15N / l4N ratios. The results showed that the Bradyrhizobium and/or Azospirillum inoculation exerted inconsistent effects on groundnut growth and nodulation as was reported by earlier workers. The total N yield and amount of N fixed were increased insignificantly by,Azospirillum and Azospirillum+Bradyrhizo¬bium inoculation. The nitrogen derived from the air was calculated to be about 72%-86% indicating that groundnut fixed more than 70% of its N need from the air. The single and combined analysis revealed that the dual inoculation and N fertilization produced high pods yield compared to single inoculation by either organism or control. The pod yield was 8% and 9% greater than the control for dual inoculation and N fertilizat¬ion, respectively. The influence of dual inoculation on groundnut growth and yield was more than its influence on nodulation and Bradyrhizobiun colonization. The results indicated that the inoculation of groundnut with Bradyrhizobium and Azospirillum brasilense could be a promising tech¬nology for improving groundnut production giving 8% increase in yield which was almost similar to the 9% increase caused by 86 kg N/ha while it is an environmentally safe process. More research is needed using different PGPR with different strains of Bradyrhizobium