XVI CONTENTS. 



CHAPTER VI. 



IMPROVEMENT OF THE SOIL. 



Sect. 1 . Improvement of the soil by the addition of earths. 

 1. By carbonate of lime. 2. By sand and gravel . . . 253 

 3. By clay. Theory of the action of clay .... 253 



Sect. 2. Improvement of the soil by draining and irrigation — Causes 

 of wetness. 



I. Draining. 1. The surface. 2. Draining the soil . . 256 



Construction of drains. Metiiod of 257 



3. Draining the sub-soil 258 



Necessity of draining 260 



Utility of draining 262 



II. Irrigation — time and mode of watering .... 262 



Sect. 3. Improvement of the soil by fallow crops and by turning in 

 green crops. 



I. Fallow crops. Naked fallows defined .... 265 

 Utility of fallow crops 266 



II. Turning in green crops. Process ..... 267 

 Theory of the action of green crops 268 



Sect 4. Rotation or interchange of crops. 

 Rotation founded on experience ...... 270 



Reasons for an interchange of crops. 



I. The structure of plants 271 



1. Culmiferous plants. Their influence in this respect . 272 



2. Leguminous plants. 3. Root crops .... 273 



II. Composition of plants 273 



III. Excretions given out by the roots ..... 276 

 Theory of M. Decandolle. Of Macaire Priueep . . . 276 

 Rules for constructing a rotation system . . . . 278 



Sect. 5. Root culture — Theory of their action. 

 CHAPTER VII. 



IMPROVEMENT OF THE SOIL BV MANURES AND TILLAGE. 



Sect. 1 . Mixed manures., or those consisting mostly ofgeine. 

 I. Solid excrements of animals. 1. Cow dung, analysis of . 284 



