Excretion of Nitrogen by Leguminous Plants

Abstract

A PREVIOUS communication¹ referred to experiments with inoculated soybeans (variety “Manchu”) growing under normal conditions in sand culture, in which I was unable to detect any excretion of nitrogenous substances from the nodules into the rooting medium, as demonstrated by Virtanen² and his collaborators in other legumes, especially the pea. Further experiments, in which the sand from the culture pots was submitted to direct Kjeldahl analysis without previous drying, have also yielded negative results. The maximum difference between nitrogen contents of the sand from inoculated and control pots was only 2·5 mgm., after four months' growth, during which time 350 mgm. of nitrogen was fixed within the nodules of the five plants of the inoculated pot. Barley plants grown in the same pots as nodulated soybeans derived no benefit from the association, confirming the absence of excretion. Three different strains of bacillus have been tried, including two of the most efficient in fixation from the Wisconsin collection, all with negative results. It is therefore clear that certain measurements of fixation and transfer of nitrogen made in a previous investigation³ under similar growth conditions are complete in themselves and do not require amendment.