Inoculation effects of Azotobacter and Azospirillum on N2-fixation and its transformations in wetland rice soil

The effect of inoculation of Azotobacter (strain BS9) and Azospirillum (strain BM9), either singly or in combination, on N-accretion and its transformation in the rhizosphere of wetland rice was investigated. Inoculation of Azotobacter and Azospirillum either alone or in a combination along with N-fertilizer (50 kg ha-1) stimulated the growth and activities of non-symbiotic N2-fixing bacteria in the rhizosphere soil of wetland rice. Inoculation with the diazotrophs increased the nitrogenase activity (C2H2 reduction) of rice roots, availability of inorganic N (exchangeable NH4 +-N and soluble NO3 --N), accumulation and mineralization of hydrolysable organic N (hydrolysable NH4 +-N, amino acid-N and hexosamine-N) in the rhizosphere soil, resulting in a greater yield of the crop. In general, single inoculation of the diazotrophs exhibited better performance than their combined inoculation. Between the two non-symbiotic N2-fixing bacteria, Azotobacter was more effective than Azospirillum in the rice rhizosphere.