irable to have soil covered with vegetation 194
Permanent pasture most economical condition of soil 194
Nitrification and rotation of crops 195

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
nitrificative micro-organisms 198
VI. Experiments by Boussingault on rate of nitrification 198
VII. Nitrogen as nitrates in Rothamsted soils after bare
fallow in lb. 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 phosphor