CONSTITUENTS OF MANURES. 173 



other mineral constituents necessary, the accumulated stores 

 of bone earth will immediately begin to develop. 



In the shape of the agricultural produce of a field, the en- 

 tire amount of these constituents which have become ingre- 

 dients of plants, is removed from the soil. 



After a series of years and a corresponding number of 

 harvests, the fertility of the soil or field diminishes ; the 

 change which is found to have taken place in the composition 

 of the soil after harvest, is the probable cause of its dimin- 

 ished or lost fertility. 



By means of solid or liquid manure or the excreta of men 

 and animals, the lost or diminished fertility is restored. 



Solid or farm-yard manure consists of decayed vegetable 

 and animal matter which contains a certain proportion of the 

 constituents of the soil ; the excrements of men and animals 

 represent the ashes of the food consumed, and which has been 

 derived from the soil. 



The urine contains the soluble, the solid excreta the insol- 

 uble constituents of the soil derived from the crops, used as 

 food, and reaped from the soil. 



By adding these to the soil, it recovers those constituents 

 which have been removed from it in the crops. 



Thus the restoration of its original composition is accom- 

 panied by the restoration of its fertility ; it is therefore certain 

 that one of the conditions of fertility in a soil is the presence 

 in it of certain mineral constituents. 



A rich and fertile ground contains more of these than a 

 poor, barren one does. 



Vegetable and animal matter and excreta when in the soil, 

 undergo putrefaction and slow oxidation ; the nitrogen of 

 their nitrogenized constituents is changed in the putrefaction 

 and decay into ammonia, and a small part into nitric acid, 

 which is the product of the oxidation or decay of am- 

 monia. 



In animal manures, therefore, not only are plants supplied 

 with the mineral substances which the soil must yield, but they 

 are also supplied with those parts of their food which the 

 plant obtains from the atmosphere ; the latter supply is a clear 

 addition to that which the air at all times aflbrds. 



In applying barn manure, some use it in large quantity and 



