156 THE PRINCIPLES OF 



I have noticed a defect with reference to the prescriptions, 

 given me as an examiner for the fertilizing of various crops. 

 I asked a question during the last examination in which the 

 student was required to prescribe fertilizing substances for 

 turnips, for wheat, and for potatoes. In the majority of 

 cases the question was answered as follows : " Wheat re- 

 quires phosphates and silica," therefore give it phosphates 

 and silica (which was a very reasonable deduction) ; 

 "turnips require a great deal of potash, therefore give 

 them potash ; potatoes require potash, therefore give them 

 potash." But it is worthy of notice that because a plant 

 requires certain substances it by no means follows that those 

 are the right substances to give it in the form of fertilizers. 

 Wheat, it is true, requires a large amount of phosphates, but 

 the long period of time which it occupies during its growth, 

 extending perhaps from September of one year to August of 

 the succeeding year, during most of which time the roots of 

 wheat are active in their search for plant food, gives it every 

 opportunity for getting phosphates. It has quite sufficient 

 time and quite sufficient root surface for obtaining all the 

 phosphates it requires out of the soil, and that being the case 

 it does not thank you for phosphates. But it is not so with 

 nitrogen. It wants the nitrogen in larger quantities, and it 

 appears to require its nitrogen more ready to its hand, proba- 

 bly because it is shallow-rooted ; but whatever the theoretical 

 reason may be, the application of nitrogen to a corn crop 

 causes a very rapid growth, and it enables the plant to well 

 push its roots through the ground, and to absorb all the 

 phosphates and other mineral matter which it requires. 



Another point of some importance with reference to the 

 use of fertilizers is this, that the effect of a fertilizer depends 

 more upon the condition of the soil than upon any other 

 factor. This renders the subject of fertilizers difficult ; it 

 renders any recommendations which we might make possibly 



