Vol. 2 No. 1
Effect of diazotrophic inoculations on nitrogen fixation and its mineralization in rice (Oryza sativa) soil.
Abstract: A field experiment was conducted during 2002 to investigate the effect of inoculation of 2 non-symbiotic N2-fixing bacteria, Azotobacter (strain AS8) and Azospiri/Jum (strain AM,), in presence of urea-N (50 kg/ha) and FYM (5 t/ha) on the performances of.the diazotrophs with respect to availability and transformation of inorganic nitrogen in the rhizosphere soils of wetland rice (Oryza saliva L, cv. PNR-381). In most cases, a successful inoculation of the diazotrophs was recorded, with the proliferation of Azotobacter and Azospirillum, either alone or in combination, in the rhizosphere soils, and nitrogenase activity (C11iz reduction) of the microbes was present in the rice roots. Inoculation of the diazotrophs substantially increased the content and availability of different fractions of inorganic (exchangeable NH; and soluble NO;) nitrogen in the rhlzosphere soils. In general, combined inoculation of the diazotrophs was most stimulative in augmenting the nitrogen status of the rhizosphere soils, which was comparable to the effects.under the uninoculated .soil series receiving 100 kg N/ha as urea-N. Between the two organisms, Azotobacter was more effective thanAzospirillum in stimulating growth and activities of the diazotrophs, in relation to accumulation and transformation of different fractions of inorganic and total nitrogen content in the rhizosphere soils. Total and exchangeable Nl-14 + nitrogel) content increased at maximum tillering to flowering stages of the crop, followed by a decline at maturity.
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