CONTENTS xi 



HAPTER PAGE 



favoring nitrogen fixation. Absorption of organic compounds 

 by plants. Associative growth of green plants and microbes. 

 Mj'corrhiza. Nodule formation by leguminous plants. Bac- 

 teriorrhiza. Summary. 



IX. Modification of the Soil PoprL.A.Tiox 203 



The soil population subject to alteration. Influence of soil 

 treatment upon the nature and abundance of microbes. Influ- 

 ence of organic matter upon the soil microbes. Influence of 

 green manures. Influence of stable manure. Artificial 

 manures. Influence of soil cultivation. Effect of Hming. 

 Influence of reaction upon soil microbes. Influence of artificial 

 fertiHzers upon soil microbes. Influence of plant gro'Ri:h. 

 Influence of partial steriUzation of soil upon the soil popula- 

 tion and its activities. Inoculation of soil with microorgan- 

 isms. The estimation of soil fertiUty by microbiological 

 methods. The activity of physiological groups of soil microbes. 

 Abundance of microbial inhabitants of soils. Biological 

 activity of the soil population as a whole. Determination of 

 the availability of specific nutrients in soils. Summary. 



X. Importance of Microbes in Soil Fertility 242 



Relationships of microbes to soil processes. Role of micro- 

 organisms in the cycle of elements in nature. Synthetic activi- 

 ties of microorganisms. Disappearance of nitrogen from the 

 soil. Nitrogen fixation in soil. Role of microbial metabohc 

 products in soil transformations. Reduction and oxidation 

 processes. Summary. 



Index 251 



