Supplying Soil Needs 177 



by steam engines. The Haber invention gives promise 

 of an increased fertilizer supply, and therefore of an 

 increased food supply for the world. 



What it takes the greatest skill of man and the most The work 

 powerful machinery to do, the nitrogen-fixing bacteria fixing" 09611 

 in the nodules of legume roots are quietly and con- bacteria 

 tinually doing all over the world changing the nitro- 

 gen gas of the air, which the plants cannot use, into 

 compounds which they can use (Chapter Four). 



Phosphorus. The form in which phosphorus is Phosphates 

 usually found in fertilizers is phosphate of lime; that 

 is, phosphorus ' combined with lime. Bones are com- 

 posed largely of phosphate of lime. Phosphorus in 

 mineral form is distributed throughout the earth, 

 but it is always combined with other elements. Pure 

 phosphorus glows in the dark, and it takes fire sponta- 

 neously if left exposed to the air. A compound of phos- 

 phorus is used in the manufacture of matches. 



Phosphorus is but slightly soluble, and it is, therefore, Loss of 

 not so easily lost from the soil by leaching as nitrogen is. ^romihe 

 A crop of forty bushels of wheat raised on an acre will soil 

 remove twenty-eight pounds of phosphoric acid from the 

 soil, the grain taking twenty-one pounds and the straw 

 seven pounds. 



Bones and phosphate rocks are the two materials out Sources of 

 of which the phosphate fertilizers of commerce are C pf^phate 

 made. Phosphate rock is found in Florida and other fertilizers 

 Southern states, and bone comes from the meat-packing 

 establishments. Both bone and rock have to be ground 

 fine to be of use, and even then the phosphate dissolves 

 very slowly in the soil. To make it more soluble, the 



