THE PRINCIPLES OF FERTILIZER PRACTICE 493 



age, (4) organic content of the soil, and (5) chemical constitu- 

 tion of the soil and its reaction. 



Although the conditions affecting fertilizer efficiency have 

 thus been so briefly disposed of, it is evident that they are of 

 vital importance in the economical utilization of fertilizing 

 materials. One point of broader scope stands out particularly 

 in this connection — the necessity of putting a soil in any' 

 given climate in the best possible condition for plant growth. 

 This means that drainage, lime, organic matter, and tillage, 

 in the order named, must be raised to their highest perfection 

 in order to realize the best results from fertilizers. 



Such considerations indicate that the decision as to the 

 amount of a single carrier or of a mixed fertilizer that should 

 be applied will be difficult and probably more indefinite than 

 formula selection. In fact, the amount of a fertilizer applied 

 to the acre is more vital than the actual chemical composition, 

 as far as money returns are concerned. 



With all the groups considered above, except garden and 

 root-crops, the applications are generally relatively light, rang- 

 ing from 150 to 350 pounds to an acre. Where excessive vege- 

 tative growth is required, as in silage, the rate may be in- 

 creased to 500 pounds. In the top dressings of meadows or 

 grains, the rate varies from 100 to 200 pounds an acre. Very 

 often this dressing is sodium nitrate or ammonium sulfate 

 alone. With garden 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 ex- 

 penditure for fertilization may be large and yet yield substan- 

 tial profits. 



278. The law of diminishing returns. — It must always 

 be remembered that in fertilizer practice the very high yields 

 obtained under fertilizer stimulation 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 in- 

 fluence of fertilization on crop yield. After a certain point 



