Aug. 3, 1908.] Agricultural Gazette of N.S.W. 661 



Besides the nitrifying bacteria, a series of other organisms occur in soil, 

 the activity of which is even more mysterious, and which benefit higher hfe 

 to a considerable extent. These are the 



Nitrogen-fixing Bacteria. 



The inertness of nitrogen has already been mentioned, and, in reahty, only 

 two phenomena in nature are known to oxidise and fix it. The one is the 

 discharge of electricity during thunderstorms, and the other the activity 

 of certain bacteria. At the high temperature produced by the lightning 

 flash the nitrogen combines with the oxygen of the air. How the bacteria 

 fix the elementary nitrogen is an entire mystery. Nevertheless quite a 

 number have been credited with the characteristic of being able to fix nitrogen 

 in a greater or lesser degree. European investigators have proved one or 

 the other, or several, to occur in almost every kind of soil. All Australian 

 soils probably contain similar organisms. In two examined by me I found 

 considerable assimilating power. The quantitative fixation of nitrogen from 

 the air is not very great in these free living organisms, but study may reveal 

 substances that Vv^ill encourage their multiplication, and consequently, produce 

 greater fixation results. They are naturally all aerobic, and therefore thrive 

 best in open, well aerated soils. A greater assimilating power than is possessed 

 by these free hving organisms may probably be assigned to the 



Nodule Bacteria. 



During a certain period of their existence these bacteria are living free in 

 the soil, but it is not known whether they multiply under such circumstances. 

 When, however, they insinuate themselves into the hair-rootlets of plants, 

 especially those of the leguminosae, they produce upon them swellings or 

 nodules, wherein they multiply enormously. They then actively assimilate 

 atmospheric nitrogen, and in some way benefit the host plant. How this 

 is brought about is not yet understood, in the face of the fact that the higher 

 plants require nitrogen in the shape of nitric acid to feed them. The fact 

 that there quasi parasites materially benefit their host by the assimilation 

 of aerial nitrogen, however has been established without reasonable doubt 

 by repeated experiments. Pots filled with sterilised soils, one of which was 

 inoculated with nodule material, have proved the effect. The inoculated 

 pots yielded larger crops, and nodules had been produced on the roots of the 

 plants, whilst on the plants of the uninoculated pots no nodules occurred. In 

 the field many similar results were obtained, and inoculation with artificially 

 reared nodule bacteria has produced remarkable results. On the other hand 

 very many inoculations in the field did not in the least benefit the crops. 

 This non-success of inoculation in the greater number of instances in my 

 opinion is mainly due to the previous presence of the bacteria in the soil 

 experimented upon. The want was already suppUed and inoculation was 

 not required. 



