CHAPTER XVIII 



Decomposition of Proteins and Other Organic Nitrogenous 

 Compounds by Soil Microorganisms 



Most of the nitrogen added to the soil by the plowing under of sod, 

 plant stubble, green and stable manures, is in the form of proteins and 

 their derivatives. The same is true of the organic nitrogenous fertilizers 

 of plant and animal origin, such as dried blood, tankage, fish scraps and 

 cottonseed meal. These substances cannot be assimilated by higher 

 plants as such but have to be first broken down into simple compounds. 

 This process is carried out in the soil by the agency of microorganisms, 

 the final product of hydrolysis being chiefly ammonia. The latter 

 is either used by the plants as such or is oxidized further to nitrates. 

 Nitrates are either assimilated by plants or by microorganisms, reduced 

 by denitrifying bacteria, or washed out in the drainage waters. 



The nitrogen content of cereal straw, corn cobs and leaves of trees 

 varies from 0.40 to 0.80 per cent; of legume hay from 2 to 3 per cent; 

 of cow manure, free from straw, about 3.5 per cent; horse manure, 

 about 1.5 per cent; chicken manure, 2.1 per cent, on an air dry basis. 1 

 When these substances are added to the soil they undergo a series of 

 transformations, largely biological in nature, involving processes of 

 hydrolysis, oxidation, reduction and synthesis. These transformations 

 result in the liberation of nitrogen in an available form which may 

 again be wholly or partly reassimilated by soil microorganisms, in the 

 presence of available energy material. 



Physical and chemical properties of proteins. Proteins are complex 

 substances, consisting of carbon, hydrogen, oxygen, nitrogen, sulfur, 

 and in some cases of phosphorus and iron. The average composition 

 of a typical protein is as follows: 



percent percent 



C 50.6-55.0 N 15.0-19.3 



H 6.5-7.3 S 0.3-2.2 



21.5-23.5 P 0-0.9 



1 Thorne, C. E. Farm manures. O. Judd Co., New York. 1914. 



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