143 THE PRINCIPLES OF 



then Baron Liebig said that the action of nitrate of soda and 

 sulphate of ammonia was not a true fertilizing action, but 

 that they acted as digesters on the mineral matters in the 

 soil, and caused certain mineral matters to pass into a state 

 of solution, in which the plant might take them up readily. 

 But Baron Liebig has passed away, and while we honour his 

 memory, we have at the same time modified a great deal of 

 what he taught us. We now believe that plants take their 

 nitrogen in a very great degree from the soil, and that nitro- 

 genous manures are among the most potent and most active 

 fertilizers that we have. It is a difficult matter to give in 

 a short space the cardinal points on such a large subject as 

 that of manures or fertilizers. It is very much easier to take 

 them in detail and discourse at length upon the merits or 

 demerits of each of the various fertilizers presented to us in 

 the market. But that is not my aim at present. I want rather 

 to draw attention to some of those general principles which 

 underlie the application of manures. In doing so it is neces- 

 sary to make a decided distinction between two great classes 

 of fertilizers, namely, general manures and special manures. 



A general manure is not a general purpose manure, and 

 a special manure is not a manure used for a special purpose ; 

 but a general manure is a manure which contains all the 

 constituents which the plant requires, and all the constituents 

 which are removed from a soil by a growing crop. A special 

 manure, on the other hand, is a substance which contains one 

 or more constituents the plant requires, but certainly falls 

 far short of the complex constitution of what is called a 

 general manure. General manures are almost always either 

 of animal or of vegetable origin. As an example you cannot 

 do better than take farmyard dung, derived as it is from straw, 

 from haulm of all kinds, and likewise from the remains of 

 food consumed by animals, and it contains all the effete 

 matter which is eliminated by the kidneys, and therefore all 





