Fixation of Nitrogen. 197 



natural product from Chile. It is thus certain that life 

 \vill never cease to exist on the earth because the supply 

 of combined nitrogen has been used up for the illimitable 

 store of the free nitrogen of the air will always serve as a 

 supply in the future as it has in the past. Present farm 

 practice, however, in the hands of many is blindly rob- 

 bing the soil of these accumulations by natural agencies; 

 in other words we are living on the capital , which has 

 been stored up. When so handled, it is only a question 

 of time before our capital will be exhausted, and then re- 

 liance must be placed on the nitrogen that is returned 

 to the soil in the form of manures and on that fixed by 

 natural means, in order to furnish the necessary amount 

 for the crops. 



A consideration therefore of the natural agencies that 

 are fixing nitrogen in the soil and elsewhere is important 

 and especially those that are susceptible of control by 

 man. Every flash of lightning causes some of the nitro- 

 gen of the air to combine with oxygen, forming, with the 

 water in the air, nitric acid which is brought to the soil 

 in the rain water. In this way a small amount of nitro- 

 gen is added to every acre each year but a comparatively 

 inappreciable quantity when compared with the needs of 

 the crop. 



The most important agencies, however, that are con- 

 cerned in the fixation of nitrogen of the air are the bac- 

 teria that are found in every soil. There are three types 

 known at the present time, one of which fixes nitrogen by 

 the help of a certain kind of green plants, the legumes, 

 the remaining kinds being able to do so independently. 

 If conditions are not favorable for the growth of these 

 bacteria in the soil practically no increase in nitrogen 

 Avill occur. It is thus essential to learn what conditions 



