496 NATURE AND PROPERTIES OF SOILS 



being by this method placed under the surface of the soil. 

 Broadcasting machines are also used, which leave the fer- 

 tilizer uniformly distributed on the surface of the ground, 

 permitting it to be harrowed in sufficiently before the seed is 

 planted,, thus preventing injury to the seed by the chemical 

 activity of the fertilizing material. 



Corn-planters with fertilizer attachments deposit the fer- 

 tilizer beneath the seed, thus avoiding a possible detrimental 

 contact. Grain-drills do not do this, and, where the amount 

 of fertilizer used exceeds 300 or 400 pounds an acre, it is 

 better to apply it before seeding. Grass and other small seeds 

 should be planted only after the fertilizer has been mixed 

 with the soil for several days. For crops to which large quan- 

 tities of fertilizers are to be added, especially potatoes and 

 garden crops, it is desirable to drop only a portion of the 

 fertilizer with the seed, the remainder having been broad- 

 casted by machinery and harrowed in earlier. 



280. Systems of fertilization. — During the evolution of 

 fertilizer practice since the middle of the nineteenth century, 

 a number of systems of applying fertilizers have been advo- 

 cated and in many cases actually followed. Perhaps the first 

 plan to be suggested was the single element system. At that 

 time, each crop was supposed to respond largely to one par- 

 ticular element. Thus, nitrogen was supposed to dominate 

 wheat, rye, and oats ; phosphoric acid, to dominate maize, 

 turnips, and sorghum; and potash to dominate potatoes, 

 clover, and beans. Present knowledge of plant nutrition and 

 the balancing effects of fertilizer nutrients show this idea to 

 be fallacious. 



The supplying of abundant minerals as a fertilizer system 

 had its origin from the fact that potash and phosphoric acid 

 are relatively cheap and are rather slowly leached from the 

 soil, while nitrogen is expensive and easily lost in this way. 

 Such a plan, therefore, always provides plenty of potash and 

 phosphoric acid, which are to be balanced each season with 



