INTRODUCTION 9 



physics, geology, and bacteriology of soils is at the 

 present time far from complete, bnt many facts have 

 been discovered which are of the greatest value to the 

 practical farmer. Of late years investigations relating 

 to the chemistry of soils and fertilizers have become 

 so extensive that the term 'agronomy' has been used 

 to designate that part of agricultural chemistry. 



In soil investigations it has frequently happened, 

 owing to imperfect interpretation of results and to 

 the presence of man}' modifying influences, that the 

 results and conclusions of one investigator appear to 

 be directly contradictory to those of another. This 

 is well illustrated in the investigations relating to the 

 assimilation of the free atmospheric nitrogen, in which 

 seemingly opposite conclusions now form a complete 

 theory. 



