CHEMICAL CHANGES 2OQ 



Molds probably do the larger portion of the work in manure 

 heaps and very peaty soils, but in ordinary arable soils bacteria 

 predominate. Most of the bacteria which grow upon gelatin or 

 agar are ammonifying. 



Bacterium mycoides, which appears to be the most im- 

 portant, decomposes albumen with the production of ammonium 

 carbonate and small quantities of formic, acetic, and butyric 

 acids, carbon dioxide, and other products. It requires the pres- 

 ence of oxygen; otherwise it reduces nitrates, if present, to 

 nitrites or ammonia. The optimum conditions for its activity 

 are a temperature of about 30, complete aeration, slightly alkaline 

 medium, and a slight concentration of the nitrogenous substance 

 in solution. 



The moisture and temperature conditions of the soil play a 

 prominent part in determining the character of the bacterial flora, 

 and hence also the character of the chemical products formed. The 

 mechanical and chemical constituents of the soil are also of de- 

 cided influence. Heavy clay or loam soils contain a greater num- 

 ber and variety of anaerobic organisms than light sandy or sandy 

 loam soils under the same conditions. But aerobic and anaerobic 

 bacteria are found in both kinds of soils. Aerobic organisms may 

 produce conditions favorable to the growth of anaerobic 

 organisms. Ammonification in the soil is due, at times, to processes 

 partaking largely of the nature of decay, and at other times of 

 putrefaction. By decay we mean the complete volatilization of 

 the organic matter, while in putrefaction ill-smelling bodies are 

 found. 



Study of Ammonification. Ammonification may be studied in 

 culture solutions, or in soils. The former is better adapted to 

 certain bacteriological studies, but methods which involve the use 

 of the soil approach more closely to natural conditions. In either 

 case, at the end of a definite period of time, the extent of the pro- 

 cess is compared by an estimation of the quantity of ammonia 

 formed. 



Brown, 1 for example, uses a culture solution composed of 10 

 1 Iowa Station Research Bulletin No. 2. 



