THE INFLUENCE OF COMBINED NITROGEN ON NODULATION AND NITROGEN FIXATION BY RHIZOBIUM MELILOTI DANGEARD

Abstract

Studies to determine the effect of various concentrations of sodium nitrate and ammonium chloride on the ability of Rhizobium meliloti to infect and fix nitrogen in three varieties of alfalfa indicated that nodulation was inhibited at high levels of combined nitrogen. High nitrate concentrations inhibited nodulation to a greater extent than high ammonium concentrations. A small amount of combined nitrogen, however, appeared to promote nodulation. Inoculated plants grown in nitrogen levels which might be encountered in the field consistently contained more nitrogen than uninoculated plants under the same treatment. There was comparatively little difference in the nitrogen content or behaviour of the varieties of alfalfa tested.