Nodulation of Hydroponically Grown Soybean Plants and Inhibition of Nodule Development by Nitrate

A procedure is described for obtaining a large number of nodules (approximately 1000) on a hydroponically grown soybean plant after a brief exposure to Rhizobium japonicum. This procedure was used to study the effect of medium nitrate upon nodulation of the soybean plant. It was found that nitrate, at concentrations equal to or greater than 2.0 mM, restricted nodule development but did not inhibit appreciably the activity or synthesis of nitrogenase in those few nodules that were formed.