G4 THE SOIL OF THE FARM. 



chemical composition of the two crops, the farmers 

 practice, when he manures wheat liberally with nitrogen 

 and gives little or none to clover, is justified. Economic 

 manuring must supplement the plant's Aveakness, while 

 it makes good tlie deficiencies of tlie soil. 



A general manure contains all the constituents of the 

 crop, or at least all those in which soils are most deficient; 

 but it by no means follows that every substance which 

 may act beneficially as a manure ought to be applied. 

 If a soil is deficient in one particular element, and con- 

 tains all the other requisites of fertility, that one sub- 

 stance may act as beneficially when applied as though it 

 were a manure containing all the constituents of the 

 crop. The crop in this case is thrown upon the natural 

 resources of the soil for all its other elements. After a 

 heavy dressing of one substance, that substance may not 

 be required for several years, but some other substance 

 may be needed ; and this all the more because the larger 

 crops now grown will exhaust such other substances 

 more rapidly than the smaller crops did previously. By 

 persisting in the exclusive use of a special manure, an 

 ultimate exhaustion of the soil is inevitable. Judiciously 

 used, special manures are the agents which bring into 

 useful activity the dormant resources of the soil ; they 

 restore the proper balance between its different constitu- 

 ents, and supply the excessive demand for some particular 

 elements. Still, the application useful on one soil may 

 be quite useless on another, and the application may be 

 useful on a soil in one season and useless in another. 



A general manure may be used year after year in a 

 perfectly routine manner, but where a special manure is 

 emploj^ed, the importance of watching its effects and 

 alterim? it as circumstances indicate, cannot be over- 

 estimated. This forces upon us the necessity for study- 

 ing the succession of manures as Avell as that of crops. 



