viii CONTENTS 



Page 



Moisture-holding Capacity of Soil 61 



Quantitative Methods for Ammonia Determination 62 



Quantitative (Colorimetric) Methods for Determining Nitrates ... 63 



Quantitative Methods for Determining Total Nitrogen 65 



Determination of Amino Nitrogen 69 



Quantitative Determination of Carbohydrates 69 



Complete Analysis of Natural Organic Material 76 



Humus Determination 78 



Carbon Dioxide Evolution 79 



Determination of Total Carbon 80 



Seed Sterilization 82 



PART IV 



The Study of Microorganisms in TjHE Soil 



A Suggested List of Arrangement of Class Exercises 87 



Apparatus for One Student 89 



Laboratory Rules 89 



A Black Finish for Table Tops . 91 



General Characteristics of the Soil Population 92 



Microscopic Examinations of Microorganisms 95 



Methods for Counting Numbers of Microorganisms 97 



Nitrogen-fixing Bacteria (and Nitrogen Fixation in Soil) 106 



Denitrifying Bacteria 121 



Nitrification 123 



Urea and Protein Decomposition 126 



Sulphate-reducing and Sulphur-oxidizing Bacteria 128 



Iron Bacteria 132 



Cellulose-decomposing Bacteria 133 



Evolution of Carbon Dioxide from Soil 136 



Literature 137 



List of Laboratories where Cultures Can Be Secured 139 



Index 141 



