FERTILIZER PRACTICE 573 



to 150 pounds an acre. ^ Very often this dressing is sodium 

 nitrate alone. With g'arden and root crops the amount 

 of fertilizer applied is very large, ranging from 800 to 

 sometimes as high as 2000 pounds. The cropping here 

 is intensive, and the expenditure for fertilization may be 

 large and yet yield handsome profits. 



It must always be remembered that in fertilizer prac- 

 tice the very high yields obtained under fertilizer stimu- 

 lation are not always the ones that give the best returns 

 on the money invested. In other words, the law of 

 diminishing returns is a factor in the influence of ferti- 

 lization on crop yield. This relationship is clearly shown 

 by the curve illustrating the law of the minimum (par. 

 469), in which the return for each increment of fertilizer 

 becomes less and less as the total quantity added becomes 

 greater. It is evident, therefore, that with an excessive 

 application of any mixture, the returns to an increment 

 will at last become so small that the increased crop fails 

 entirely to pay for even the fertilizer, not to mention such 

 charges as cost of application, harvesting of increased 

 crop, storage, and the like. The application of moderate 

 amounts of fertilizer is to be urged for all soils until the 

 maximum paying dose that may be applied to any given 

 crop is ascertained by careful experimentation. Over- 

 fertilization probably accounts for the fact that such a 

 large proportion of the fertilizers sold to the farmers each 

 year not only is entirely wasted, but probably in some 

 cases even becomes detrimental to crop yield. 



480. Systems of fertilization. During the evolution 

 of fertilizer practice, particularly since the early part 

 of the nineteenth century, a number of systems of apply- 

 ing fertilizer have been advocated or have been in actual 

 use. These may be listed as follows : 



