242 AGBICULTUKAL AND INDUSTRIAL BACTERIOLOGY 



deaminized in an analogous fashion. In general, it may be 

 noted that practically any organic compound of nitrogen is 

 eventually broken down by soil microorganisms with the 

 formation of ammonia. 



Well-aerated soils show little tendency for ammonia to 

 accumulate. As rapidly as it is formed it is changed by the 

 nitrifying bacteria, but under anaerobic conditions, such as 

 exist in the mud in the bottom of a pond or in water-logged 

 soil, the nitrogen remains more or less indefinitely in the 

 form of ammonia. Not infrequently the fact that the am- 

 monia is usually oxidized in arable soils and the nitrogen 

 available to the roots of green plants, therefore, is generally 

 nitrate, has led to the erroneous assumption that green 

 plants cannot take up ammonia through their roots. In 

 general, this is a fallacy. In fact, many kinds of plants, 

 particularly those which live with their roots in wet or 

 water-logged soils or in mud, secure practically all of their 

 nitrogen in the form of ammonia. However, ammonia is 

 relatively volatile and would be readily lost from the soil 

 and manure were it not for the fact that it is, in the pres- 

 ence of oxygen, readily oxidized to nitrites and nitrates. 



Inasmuch as the rapidity with which the microorganisms 

 in a given soil can bring about complete proteolysis and 

 ammonification of nitrogenous manures added is one of 

 the indices to soil fertility, methods have been devised for 

 testing out this soil power in the laboratory. The test is 

 carried out by adding a- given amount of a particular 

 nitrogenous material, such as casein, blood meal or other 

 organic nitrogenous compound, to a given weight of the soil 

 to be tested, mixing thoroughly, placing in suitable vessels, 

 usually tumblers, adding water to the optimum and incu- 

 bating. At the end of a given period of time these samples 

 of soil together with similar samples to which no manure 

 has been added are analyzed for their ammonia content. 



Until recent years it has generally been thought that the 



