102 THE PRINCIPLES OF AGRICULTURE 



they tend to form insoluble compounds with 

 soil constituents. The more vegetable matter 

 a soil contains, the less pronounced is the 

 action of leaching. As a rule, commercial ferti- 

 lizers are applied after the ground is fitted, and 

 then harrowed in or drilled in. 



165. The amounts and kinds to apply are 

 determined by (a) the analysis of the material 

 (that is, its richness in plant-food), (&) its 

 cost, (c) the richness of the soil in plant-food, 



(d) the tilth or texture of the soil (60, 49a), 



(e) the kind of crop, (f) the kind of farming, 

 whether intensive or extensive (111, lllfr). It 

 follows, therefore, that the mere analysis of 

 the soil and the plant cannot determine what 

 fertilizer it is most profitable to use. 



166. What fertilizers to use, and how to 

 apply them, are subjects which are discussed 

 in bulletins and books by many authors ; but 

 even after reading all the literature, the farmer 

 must experiment with his own land and his own 

 crops, to determine just what materials are most 

 profitable for his use. In other words, the ad- 

 vice as to fertilizers is more valuable in teach- 

 ing a man principles, in suggesting means of 

 experimenting, and in designating the proba- 

 bilities of any line of action, than in specifying 

 just what fertilizers one shall use. An area on 

 one side of a field may be devoted to such 



