226 



MODIFICATION OF THE SOIL POPULATION 



soil, and it accumulates as ammonia, since the nitrifying organisms 

 are destroyed by the partial sterilization treatments. When the 

 nitrifying bacteria again become established in the soil, the ammo- 

 nia is converted to nitrate and only small quantities of ammonia are 

 subsequently found in the soil at any one time. The increased 

 rate of production of both carbon dioxide and ammonia clearly 

 indicates that the soil organic matter is undergoing more rapid 

 decomposition as a result of the treatment. 



Untreated Soil 



Soil Plus Toluene, 

 Relnoculated 



Soil Plus Toluene, 



Soil Air -Dried, 

 Reinoculated 



Soil Air -Dried 



Soil Plus CSz, 

 Reinoculated 



Soil PlusCSa 



Soil Heated, 

 Reinoculated 



Soil Heated 



100 150 200 



Carbon Dioxide Evolved -Mgm. 



250 



300 



Fig. 80. — The influence of partial sterilization treatments on biological activi- 

 ties in soil as reflected in the formation of carbon dioxide during the first week 

 after treatment (mgm. COo per kgm. of soil). In some cases the soils were 

 reinoculated with infusion of fresh soil after treatments (after Wakeman 



and Starkey). 



Many compounds in the soil are modified by heat and anti- 

 septics, as evidenced by the greater solubility of both the organic 

 and inorganic soil constituents. Besides the modification of the 

 inanimate material, there is to be taken into consideration also 

 the destruction of large numbers of living soil organisms. The 

 soil may thus be altered in many ways by partial sterilization, 

 these alterations leading to or being responsible for an increase in 

 productivity. 



To explain some of these phenomena, Russell and Hutchinson 

 suggested the following ingenious hypothesis. It is known that 

 the soil harbors, in addition to bacteria, various other groups of 



