Contents xiii 



PART IV 



Pages 



Bacteria in Relation to Soil Fertility . 135-302 



CHAPTER XV 



Number and Distribution op Bacteria in the Soil . 135-143 

 Number of bacteria in soil — Distribution of bacteria 

 in the soil. 



CHAPTER XVI 



The Relations or Bacteria and Humus . 144-154 



The quantity of humus as affecting number of bacteria — 

 Quality of humus as affecting number of bacteria. Bac- 

 teria and the decomposition of soil-humus. 



CHAPTER XVII 



Bacteria and the Transformation of Soil-Nitrogen . 155-1Q7 

 The source of nitrogen in the soil — Proportion of nitro- 

 gen in the soil— Nitrogen compounds in the soil-humus — 

 Loss of nitrogen in the soil — Availability of nitrogen — 

 Conditions affecting availability of nitrogen — Soil bac- 

 teria — Ammonification — Ammonifying bacteria — En- 

 zymes — Mutual relations of bacteria — Denitrifying bac- 

 teria — Influence of bacteria on one another — Ammonify- 

 ing power of soils. 



CHAPTER XVIII 



Nitrification . 168-182 



True character of nitrification— Pure culture of nitrify- 

 ing bacteria — Importance of nitrification — Conditions 

 affecting nitrification — Loss of nitrates in the soil — 

 Sources of nitrates — Early use of nitrates — Conditions 

 influencing the formation of nitratefe — Availability of 

 nitrogenous materials — Influence of crop on availability. 



