Under the laboratory conditions, extra nitrogen sources are not needed in free living diazotrophs, and carbon sources (such as sucrose, glucose) and a small amount of inorganic salt are needed to the medium. Free living diazotrophs can directly use nitrogen (N2) in the air as nitrogen nutrition. However, while cultivating several symbiotic diazotrophs such as rhizobia, it is necessary to add nitrogen nutrition, because rhizobia and other symbiotic nitrogen-fixing bacteria can not use molecular nitrogen (N2) in free living form.
