204 AMMONIFICA TION 



according to Lipman, in stimulating the activities of the decay 

 bacteria. Thomas slag increases the production of ammonia to 

 a considerable extent. Where acid phosphate is applied to a soil 

 the increased ammonification resulting, according to McLean and 

 Wilson, is due to fungi rather than to bacteria, but this would 

 probably vary with the magnesium and calcium carbonate content 

 of the soil. 



Chemistry of the Process. Rettger and his associates have shown 

 that bacteria are unable to attack or bring about the decomposition 

 of proteins without the aid of enzymes or other proteolytic agents, 

 whereas Itano using the formal titration method of Sorenson has 

 shown that B. subtilis produces a gradual increase of formal-titrating 

 nitrogen for a period of two hundred and forty hours. The greatest 

 proteolysis took place toward the optimum hydrogen-ion concentra- 

 tion. He, therefore, suggested that the enzyme is probably tryptic- 

 like in nature, and endocellular. Moreover, as was seen in the preced- 

 ing chapter, a number of amino-acids have been isolated from the soil. 

 Hence it is most natural to assume that the disintegration of pro- 

 teins in the soil is primarily protein hydrolysis catalyzed by endo- 

 or exo-enzymes secreted by the decay bacteria. The enzymes- 

 pepsin, trypsin, erepsin, and probably other protoclastic enzymes- 

 are capable of hydrolyzing proteins with the formation of some 

 eighteen amino-acids. The number and quantity of each depends 

 upon the specific protein hydrolyzed. Incomplete hydrolysis 

 results in the production of a number of intermediate substances 

 variously designated in the order of decreasing complexity 

 proteoses, peptones, and polypeptids. 



Taylor suggests the scheme given on page 205 as indicating the 

 stages in the hydrolysis of the protein molecule. 



There are reasons for believing that in the process of ammonifica- 

 tion the hydrolysis is similar to this, for Marchal showed that the 

 ammonifiers are capable of hydrolyzing proteins, proteoses, and 

 peptones. Moreover, many of the protein hydrolytic products are 

 found in the soil, and Miyaka has shown from a mathematical 

 analysis that the process of ammonification is an autocatalytic 

 chemical reaction in which the increase of ammonia in the process 

 is in accordance with the formula : 



Log- x 



= K(t-ti) 

 A-x 



Where x is the amount of ammonia which has been produced at 

 time (t), a is the total amount of ammonia produced during the 

 process, K is a constant, and t\ is the time at which half of the total 

 amount of ammonia is produced. 



