CONTENTS. XV11 



APPENDIX TO CHAPTER IV. 

 NOTE 



I. Old theories of nitrification . . . . . .196 



II. Nitrification takes place in solutions devoid of organic 



matter 196 



III. Oxidising power of micro-organisms in soils . . .197 



IV. Effect of urine on nitrification in soils . . . .197 

 V. Solution used by Professor Frankland in cultivating nitri- 



ficative micro-organisms . . . . . .198 



VI. Experiments by Boussingault on rate of nitrification . 198 

 VII. Nitrogen as nitrates in Rothamsted soils after bare fallow 



in Ib. per acre ........ 198 



CHAPTER V. POSITION OF PHOSPHORIC ACID IN 

 AGRICULTURE. 



Occurrence of phosphoric acid in nature 199 



Mineral sources of phosphoric acid ...... 200 



Apatite and phosphorite ........ 200 



Coprolites 201 



Occurrence of phosphoric acid in guanos ..... 202 



Universal occurrence in common rocks ..... 202 



Occurrence in the soil ........ 203 



Condition in which phosphoric acid occurs in the soil* . . 203 



Occurrence in plants ........ 204 



Occurrence in animals 205 



Sources of loss of phosphoric acid in agriculture . . . 205 

 Loss of phosphoric acid by drainage . . . . .206 



Artificial sources of loss of phosphoric acid .... 206 



Amount of phosphoric acid removed in milk . . . . 207 



Loss of phosphoric acid in treatment of farmyard manure . 208 



Loss of phosphoric acid in sewage 208 



Sources of artificial gain of phosphoric acid .... 208 



APPENDIX TO CHAPTER V. 



NOTE 



I. Composition of apatite (Voelcker) 210 



II. Percentage of phosphoric acid in the commoner rocks . 211 



CHAPTER VI. POSITION OF POTASH IN AGRICULTURE. 



Potash of less importance than phosphoric acid . . .212 

 Occurrence of potash 213 



b 



