FERTILIZERS 



77 



plant is provided in the carbon dioxid (CO 2 ) of the air. Oxygen 

 is also derived from air (187). When the plant is burned, the 

 six mineral elements remain in the ash. 



161. The ash is but a very small part of the total weight 

 of the plant. In a corn plant of the roasting-ear stage, the 

 ash (what remains after ordinary burning) is about one per 

 cent of the total substance. A good wheat crop will require 

 per acre about ten pounds of phosphoric acid and about 

 thirty pounds of potash. The amount of phosphoric acid 

 removed by 200 bushels of 



potatoes is nine pounds; and 

 of potash sixty pounds. 



162. The farmer does not 

 add all the elements to the soil 

 in the shape of fertilizers. Some 

 of the nutrient elements are 

 used in such small quantities 

 and are present in the soil to 

 such an amount that the ad- 

 dition of them is not necessary. 

 The farmer adds nitrogen, pot- 

 ash and phosphorus to the land 

 to provide' nutrients, and he 

 also adds calcium in lime or 

 land-plaster because of its 

 chemical and physical effect on 

 the soil. Some of the fertilizers 

 are mined, others are by-pro- 

 ducts of packing-houses and 



other manufacturing establishments. Stable manure is gen- 

 erally considered to be the best single fertilizer. 



163. Nitrogen is one of the most essential elements 

 required by the plant. It is expensive to add to the soil as 

 fertilizer. Fortunately, nature has provided a method 

 whereby some of the inexhaustible nitrogen supply of the 



