Contents xiii 



PART IV 



Pages 

 BACTERIA IN RELATION TO SOIL FERTILITY . . 135-302 



CHAPTER XV 



NUMBER AND DISTRIBUTION OF BACTERIA IN THE SOIL . . 135-143 

 Number of bacteria in soil Distribution of bacteria 

 in the soil. 



CHAPTER XVI 



THE RELATIONS OF 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 . 155-167 

 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 nitrates Availability of 

 nitrogenous materials Influence of crop on availability. 



