610 T. J. MURKAY 



In general, fixation proceeds better in soils than in solution, 

 more nitrogen being fixed in soils. The nitrogen fixed per gram 

 of mannite is higher with the soils than in solution. The greater 

 amount of nitrogen fixed in soils may be due of course to other 

 forms of energy in the soil in the shape of decomposed plant 

 tissue. Nitrogen is fixed readily under aerobic or anaerobic 

 conditions in solutions. In soils, nitrogen fixation proceeds better 

 under anaerobic conditions. 



DENITRIFIC ATI ON 



Broadly speaking, denitrification is the breaking down of 

 nitrates to nitrites and ammonia and the liberation of free 

 nitrogen. More narrowly it includes only the latter phase, the 

 liberation of free nitrogen by microorganisms acting on nitrates 

 or nitrites. It is with this latter phase that my experiments 

 were concerned. The importance for agriculture of denitrifica- 

 tion in the soil has been greatly exaggerated. It is important 

 if large amounts of fresh manure are added to soil rich in nitrates, 

 but not otherwise. 



Denitrification is carried out by a variety of microorganisms, 

 chief among which are B. denitrificans, B. pyocyaneus, B. fluo- 

 rescens-liquefaciens, and B. Hartlebii. Lipman (1902) found 

 from 1.3 per cent to 25.6 per cent loss in nitrogen with pure 

 cultures and as high as 35 per cent loss with mixed cultures. He 

 also states that denitrifying organisms are found in all soils. 

 These denitrifjdng organisms live in the presence of air but may 

 live anaerobically. 



Koch and Pettit (1910) found that denitrification varies with 

 the moisture present. With an increase in moisture there is an 

 increase in denitrification, and as the moisture is increased under 

 laboratory conditions there is an increase in the nitrogen lost. 



Jensen (1909) has pointed out that denitrification is always 

 accompanied by oxidative processes. 



My study of denitrification was carried out both in soils 

 and in solutions. For the solution work the following medium 

 was used — Giltay and Aberson's solution: 



