INFLUENCE OF STABLE MANURE 209 



Influence of Stable Manure. — The addition of stable 

 manures to the soil results in modifications of the soil population 

 in three distinctly different ways: (1) The various constituents of 

 the manure, namely, the straw, faeces and urine, offer favorable 

 and readily available sources of energy, nitrogen and minerals 

 (especially phosphates and potassium salts) to many different 

 microorganisms. (2) Manure contains large numbers of a variety 

 of microorganisms that have originated in the digestive system of 

 the animal; the addition of considerable quantities of manure to 

 the soil may thus considerably modify the soil population through 

 actual mass inoculation. (3) The addition of manure leads to 

 modifications of the physical condition of the soil. The general 

 results of all these effects is the creation of an environment more 

 suitable for the development of higher plants. 



An understanding of the nature and composition of animal 

 manures makes possible an explanation of the changes taking 

 place during their decomposition and suggests an interpretation 

 of the fertilizing values of the manures in comparison with ordinary 

 plant residues; the latter are quite different in composition from 

 the stable manures. This is the result of at least three factors: 

 (1) in many cases the chemical nature of the food of animals is 

 different from the organic matter entering the soil with the plant 

 roots and stubble; (2) the organic matter consumed as food by 

 animals is greatly altered during its passage through the digestive 

 systems of the animals; (3) a large part of the nitrogen in the 

 manure is in a readily assimilable form, and another part is in the 

 form of microbial cells. 



During animal digestion, the more readily decomposable sub- 

 stances of the feeds are removed from the organic matter and, 

 consequently, the excreted material represents substances more 

 resistant to decomposition than the original food. The animals 

 consume practically all of the sugars and a large portion (70 to 

 80 per cent) of the fats, starch, hemicelluloses, and cellulose. The 

 lignin is removed to a slighter degree than any other group of the 

 organic substances in the foods. The manure consequently con- 

 tains a much higher percentage of lignin than the food which was 

 consumed. It is apparent that the composition of the food mate- 

 rial has an effect on the composition of the excreted material; 

 the foods containing the most lignin will be least digested. 



During the passage of the food material through the digestive 



