Effects of Temperature, Nitrogen Fertilization, and Plant Age on Nitrogen Fixation by Setaria italica Inoculated with Azospirillum brasilense (strain cd).

The association between the nitrogen-fixing bacterium Azospirillum brasilense (strain cd) and the grass Setaria italica was studied under different environmental and soil conditions. Highest acetylene reduction rates in intact plants were observed at the booting stage of Setaria (2350 nmol ethylene produced hour(-1) plant(-1)) at 27 C. Higher temperatures, up to 32 C, enhanced ethylene reduction. Significant increases in shoot dry weight, panicle weight, and length were obtained in inoculated plants fertilized with suboptimal NH(4)NO(3) levels. The increase in nitrogen content of plants inoculated with A. brasilense was shown to be due to N(2) fixation. This was demonstrated by growing plants in washed quartz sand with no combined nitrogen. The bacteria also increased branching and development of roots. It was concluded that inoculation of Setaria with A. brasilense may lead both to increases in plant yield and saving of nitrogen fertilizer.