Methods of Use of Fertilizers 197 



removed in amounts in excess of the others. On the other 

 hand, the cropping may have been such as to be fully as 

 exhaustive in the sense that the total quantity of constitu- 

 ents removed is quite as great, though since they are 

 removed in more uniform proportions, the period of prof- 

 itable cropping is extended, and the fertility needed in- 

 cludes all the essential elements, rather than one or two. 

 That is, the grain, hay and potatoes may have been grown 

 in rotation, each removing one or the other in greater 

 proportion, but because they differ with each crop, no 

 one is exhausted before the other; and thus when the 

 land reaches the time when it would no longer profitably 

 grow those crops, an application then of all of the con- 

 stituent elements would result in a greater and more 

 profitable increase in crop than if the fertilizer contained 

 one constituent only. The previous treatment and crop- 

 ping of soils, therefore, is an important guide in determining 

 the most economical method of fertilization. 



Furthermore, in this matter of cropping as a guide to 

 possible need of fertilization, it must be remembered that 

 a continuous one-crop practice is more productive of total 

 loss of constituents than a practice which includes such 

 renovating crops as clover, or one which permits of a more 

 constant occupation of the land, since in the former, the 

 introduction of clover reduces the need for nitrogen fer- 

 tilization, and in the latter, the vegetable matter is not so 

 rapidly used up, and the loss of mineral constituents by 

 mechanical and other means is very much reduced, because 

 of the constant occupation of the land. 



The influence of character of crop. 



The financial result from the application of fertilizers 

 is also influenced in a very large degree by the character 



