304 AGRICULTURAL TEXT-BOOK. 



to the soil those constituents \vhich are necessary for the formation of 

 the plant we wish to grow, and which, in a soluble shape, are eitlijr 

 naturally deficient in the soil, or have become so by our carrying them 

 off in the form of grain, meat, &amp;lt;tc., we not being able to wait until nature 

 performs this work for us,* 



670. Manuring is probably the most costly mode of restor 

 ing the fertility of the soil that can be practiced. 



671. But while many persons are content merely to retain, by 

 manuring, their land at its natural point of fertility, others ren 

 der it much more fertile than it ever was; on the principle that 

 if a certain quantity of applied manure can be worked up into 

 ,1 grain crop, a still greater quantity will supply a larger propor 

 tion of grain. 



672. From this it must be apparent that in order that a 

 farmer may economically and skilfully manure his land, he must 

 understand the composition of plants, the relative materials 

 which constitute his soil, the constituents of the manures ap 

 plied, and their chemical action. For were he to put on his 

 field a salt in a soluble form which would immediately become 

 insoluble in consequence of chemical changes, the manure 

 would be lost to him. 



In the following pages we shall chiefly confine ourselves to an ac 

 count of the manures which are generally available in the Northern 

 States, and the principles on which they act. For further information 

 on this extended and intricate subject we must refer the reader to works 

 especially bearing upon it. 



673. The following diagram from Dumas & BonssingauW s Chemical 

 and Physiological Balance of Organic Nature, may be useful in this 

 connection. 



A species of manurnig may be practiced, the principle of which differs from th 

 above; as where a salt is applied, wot for the purpose of directly entering info the 

 plant, but to net, chemically, as a solvent, upon the insoluble constituents of the soil; 

 o as a fixer of gases, or other to&quot;&quot; readily soluble materials, as charcoal nnd proba 

 bly plaster. 



