THE CULTURE OF FARM CROPS. 



PART FOURTH. 



CHAPTEK XXIX. 



THE IMPROVEMENT OF THE SOIL BY CHEMICAL 

 MEANS. ANIMAL MANURES. 



The various methods of improving soils by chemical 

 means, are based upon the following principles which have 

 been already explained. 



First. Plants obtain from a fertile soil a variable pro- 

 portion of their organic nutriment, and the greater part of 

 their nitrogen is derived from this source. 



Second. The inorganic food which they require, they 

 procure solely from the soil. 



Third. Different kinds of plants require a special supply 

 of different kinds of inorganic food, or of the same kinds in 

 varying proportions. 



Fourth. Soils vary considerably in respect of the va- 

 rious inorganic compounds they contain, some soils may be 

 deficient in some of them, and others may contain an 

 abundance of all of them; therefore the growth of plants 

 upon various soils differs accordingly. 



The whole art of improving the soil by chemical means, 

 or of manuring and fertilizing it is based upon these few 

 principles. 



There are three distinct methods of improving the soil in 

 this way. 



First; by removing from it some injurious substance, and 

 affording it an outlet by means of drains, in a word, by 

 draining. 



Second; by the addition of some substance which may re- 

 move, or change the character of noxious substances; or so 

 change inert substances as to make them available by them- 



