Specific Elements of Manures Nitrogen. 5 



equal extent. A thorough knowledge of the composition of 

 special artificials, and of the conditions under which they act 

 most beneficially, is therefore of much value to the farmer, as it 

 enables him to apply fertilizers of that description with the 

 greatest advantage. There are, however, others which, notwith- 

 standing the deficiency of some constituents, can be, and are, 

 used successfully for various kinds of crops. In reality, the 

 deficiency of some constituents, instead of being a defect, is a 

 recommendation to these manures ; for several of the consti- 

 tuents which greatly preponderate in farmyard-manure are 

 present in most soils in abundant quantities ; they need not 

 therefore be supplied to the land in the form of manure ; or 

 should they be wanting in the soil, they can be readily obtained 

 almost everywhere at a cheap rate. If, therefore, these inex- 

 pensive and more widely-distributed substances are dispensed 

 with in compounding a manure, and only those -are selected 

 which occur in soils in minute quantities only, a very valuable 

 and efficacious fertilizer is obtained, which possesses the great 

 advantage of containing in a* small bulk all the essential fertiliz- 

 ing substances of a large mass of home-made dung. 



In one sense, all the fertilizing agents are alike valuable ; for 

 they are all indispensable for the healthy condition of our cul- 

 tivated crops, and consequently the absence of one is attended 

 with serious consequences, though all others may be present in 

 abundance. Thus the deficiency of lime in the land may be 

 attended with as much injury as that of phosphoric acid. In 

 this sense lime is as valuable as phosphoric acid ; but inasmuch 

 as lime is generally found in most soils in abundant quantities, 

 or, if deficient, can be applied to the land more economically in 

 the form of slaked lime, marl, shell-sand, &c., its presence in an 

 artificial manure is by no means a recommendation to it. 



The efficacy of manure therefore depends not only on its com- 

 position but also on that of the soil, and let us add, likewise, 

 on the requirements of the crops intended for cultivation. It is 

 well, also, to bear in mind that the substances which soils gene- 

 rally contain only in minute quantities are exactly those which 

 plants require in much larger proportions than the constituents 

 which abound in soils. 



The efficacy of a manure consequently depends in a great 

 measure on the amount of the more rare and valuable consti- 

 tuents. In estimating the probable effects of a manure, it is 

 very important to entertain correct views with respect to the 

 comparative value of the component parts of manures. 



It has been shown by practical experience that nitrogen in 

 the form of ammonia or nitric acid, phosphoric acid, and potash 

 are the most efficacious and valuable constituents of all manures. 



1. Nitrogen in the form of ammonia, nitric acid, or animal 



B3 



