THE PRINCIPLES OF FERTILIZER PRACTICE 497 



sufficient nitrogen to give paying yields. While this system 

 is not feasible in its entirety at the present time, the prin- 

 ciple involved is worthy of incorporation with more economi- 

 cal plans. 



A system based on the amount of nutrients removed by 

 crops has received from time to time considerable support. 

 According to this plan, as much plant-food material is added 

 each year as will probably be taken out by the plant, this 

 being determined by chemical analyses of the crop. The 

 system not only overlooks the fact that diverse plants feed 

 differently on the same soil, but that the same crop exhibits 

 marked variability with change of season and change of soil. 

 Moreover, no allowance is made for losses by leaching, which 

 are known to equal at times the losses due to plant absorption. 



In trucking or in general farming operations, one crop is 

 often the money crop. Naturally its stimulation by heavy 

 fertilization will pay better than applications to crops that 

 bring less on the market. The general plan in this system 

 is to allow the crops following the money crop to utilize 

 the residuum. When this residual influence works out fa- 

 vorably, the system is likely to be a profitable one ; but when 

 the following crops fail to respond, the method becomes 

 wasteful in the extreme. 



281. Rational fertilizer practice. — In the selection of a 

 system that will result in an effective utilization of fertilizers, 

 only two of the plans described above need be considered. In 

 any fertilizer, phosphoric acid and usually potash should 

 always be present in amounts sufficient more than to balance 

 the nitrogen, since the activity of nitrogen is so pronounced. 

 Therefore, a scheme that calls for an abundance of minerals 

 is a sound one. This, coupled with the heavy fertilization 

 of the money crop, does not, however, constitute what might 

 be considered a rational system, since the crops that follow 

 may or may not be adequately supplied with nutrients. 



Not only must the soil, the crop and the fertilizer formula 



