CHAPTER VII. 

 PHOSPHORUS, ITS SOURCES AND USE IN PLANT FEEDING. 



The second important element in the nutrition of plants and the matur- 

 ing of crops is phosphorus. This element, like the other elements which 

 enter into the feeding of plants, is never used as a pare element, but always 

 in the form of phosphoric acid. This is a highly oxidized compound of hy- 

 drogen and phosphorus, and forms, with alkaline bases such as lime, etc., salts 

 known as phosphates. The most commonly available form is the phosphate 

 of lime. This is a large constituent of the bones of all animals, and is found 

 in nature in the phosphatic rocks and coprolites. In the basic process of steel 

 making, large amounts of phosphates are separated from the iron ore and left 

 in the furnace slag, and this slag is one of the important sources of phosphoric 

 acid for fertilizing purposes. In many of the sea islands where there 

 is a heavy rainfall, the guano deposits have been largely composed of the 

 phosphate of lime, the nitrogen having been washed away. Large 

 deposits of phosphatic rock are found all along our South Atlantic 

 coast, and in the Mississippi valley and elsewhere. The origin of these 

 deposits has been a matter of much discussion among geologists. 

 The idea generally prevails among most farmers that these are the 

 petrified bones of extinct animals, but this is far from being correct, 

 though there are certainly many fossil remains found associated with 

 the phosphatic rocks. Phosphatic guano is certainly the remains of the ex- 

 crement and food refuse of sea birds, and coprolites and phosphatic nodules 

 are thought to be the remains of animal excrement. But, whatever their 

 origin, the importance of the deposits has long been recognized; for the 

 replenishing of our soils with phosphates is one of the greatest of the problems 

 that confronts the cultivator, since in all cultivation, and in the raising of 

 domestic animals, the phosphates are continually being removed from the 

 farm. Unlike the nitrogen we cannot get phosphates from the air, and there 

 are but two wa}^s in which the loss to the farm in phosphates carried off from 

 it can be made good. We must either feed on the farm food grown elsewhere, 

 or we must buy the phosphates when they are deficient. Inasmuch as the 

 localities are few where the feeding of purchased food can be made a profitable 



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