Abstract
In the present study the nitrogenase activity of Nostoc muscorum and Nostoc rivulare was evaluated in vitro; the test showed that Nostoc muscorum and Nostoc rivulare have the ability to fix nitrogen. In a pot experiment under field conditions, the results of the present study showed that inoculation of the soybean plant with Nostoc muscorum and Nostoc rivulare, either alone or in combination with N-fertilizer at 50 and 100 kg N/ha, caused a significant increase in the growth of these plants, as reflected in plant height, leaf area, weight of plant as well as the legume weight of soybeans. The combination of biofertilization and N-fertilization, especially at 100 kg N/ha, had more effect on both the growth of soybeans and nitrogenase activity compared to biofertilization alone. Nostoc muscorum and Nostoc rivulare are a promising biofertilizers for achieving an efficient association between N-2 fixing cyanobacteria and soybeans; and thus enhancement of the growth.