OF THE PRKCEPTNO CHAPTERS. 



m 



Injuries arising from wetness of the soil. It causes 

 the formation of vegetable acids, and other hurtful sub- 

 stances. 



These defects to be removed by draining. 



Drains to be 30 to 36 inches deep, and always tO' 

 ▼ered. If made of stones, these should be broken 

 ■feall; if of tiles, these may be either of the round, 

 oval, or horseshoe shape. The earth to be rammed 

 hsfd above them in all cases. They ought to run 

 straight down slopes, and be placed 24 to 50 ieet 

 ^>art. 



Subsoil and trench ploughing; difference in the two 

 operations, and nature of their effect 



The inorganic substances of the soil are found in 

 plants, with the single exception of alumina. 



The quantity of some of them is quite small in 

 pbatSy Imt all are absolutely Deccosuy. 



CHAPTER VIL 



EJfed of cropping upon the toil. 



Biflerent crops take away the i *<• substances 



of the soil in ditferent proportion cish also va* 



ries in composition. 



The grains contain chiefly phosphates. 



Potatoes and tuniips, mostly potash and soda. 



Grasses, for the roost part. '?•"•• Mt«i «;iica; straws, 

 nearly all silica. 



This explains the principle oi rotiuiun. One crop 

 may find food when the land has been exhausted for 

 another, and so a succession may be continued for 

 some years. 



' ue of land is kept up by such a course for a 



gi' ^ . reasod hiiirtli of film'. 



