Nitrogen fixation by soil microorganisms

Abstract

From the results presented it may be permissible to point out the following:Fungi are responsible for the fixation of very small quantities of nitrogen, while theAzotobacterandB. amylobactergroups are the important nitrogen fixers in the soil.B. amylobacteris able to fix from 4 to 5 mg. of nitrogen per gm. of dextrose consumed.B. amylobacterhas an optimum range ofpH. between 6·0 and 7·0, and Azotobacter between 7·0 and 8·4.Azotobacterutilises the organic acids produced during the fermentation of dextrose as sources of energy for nitrogen fixation in the absence of dextrose.B. amylobaclerdoes not, or does only to a limited extent, utilise such products.Large quantities of dextrose do not favour an efficient nitrogen fixation, as large quantities of the organic acids produced effect the reaction of the media rendering the organisms inactive.The nitrogen fixing organisms seem to be equally well represented in the heavy and light soils.