26 IIANDT-BOOK OF HUSBANDRY. 



of the vegetable matter from which the soil was formed, are from 

 one to three pounds in each one hundred pounds of other sub- 

 stances which go to form the ashes of all cultivated plants, and 

 the fertility or barrenness of any soil which is in good condition 

 in other respects, depends on the presence or absence of these 

 parts. All soils, once fertile, which, without growing more wet, 

 have become unproductive (which have been exhausted) through 

 an improper system of cultivation, have become so in consequence 

 of the removal of the available supply of 6ne or more of this 

 class of ingredients, and their fertility can be restored only by the 

 addition of the missing substance, by the application of some 

 agent like lime or unleached wood ashes, or by deeper plowing, 

 better draining, the use of green crops, or exposure to the 

 action of frost. The first process is a direct return of the 

 materials which have been taken away ; the others either bring 

 up similar matters from the unexhausted subsoil, or, by causing the 

 corroding, or the pulverization of coarser particles of the soil, 

 they expose to the action of roots, the same constituents, which 

 had been locked up within them. 



The following table gives the names of the most important of 

 these plant-feeding materials, and the proportion which they bear 

 to the whole weight of the soil : — * 



Phosphoric acid I lb to 4 lbs in 1000 lbs of soil 



Sulphuric " i " 3 " " " " 



Magnesia 5 " 10 " " " " 



Chlorine I " 1 " " " " 



Soda 3 " 8 " " " " 



Potash I " 20 " " " " 



In all, from 1 1 J- " 47 " " < " 



These proportions vary a good deal within certain limits, but 

 they are always exceedingly small. Lime varies very much more 

 widely. 



To sum up the case, then, the soil, in a practical point of 

 view, may be regarded as a mass of material, which admits the 



* For greater simplicity, I make no account of the silicates, oxide of iron, and oxide of 

 manganese, and which should be considered in a scientific treatment of the subject ; but 

 which are not of great practical importance in this connection. 



