398 AGRICULTURE OR MAINK. 



PURCHASED PLANT FOOD. 



While there are twenty odd elements that enter into the com- 

 position of plants, nitrogen, phosphorus, potassium and calcium 

 are the important ones added in commercial fertilizers. Although 

 an acre of fertile soil contains tons of nitrogen, phosphoric 

 acid and potash, they are usually in forms unavailable to plants. 

 Growing plants take up and carry off in the resulting crops a 

 large amount of available nitrogen, phosphoric acid, potash and 

 lime in a given soil. If the crops are fed upon the farm and 

 the resulting manures are saved, a large part of the manurial 

 matter in a good available form will be returned to the land. 

 If, however, the crops are sold off the farm, the farm is depleted 

 by this loss of plant food which must be made good in some 

 way or other. Usually manures are applied to soil for the 

 double purpose of applying plant food in an available form 

 and unlocking the unavailable compounds which are already in 

 the soil. 



New England agriculture has been dependent for the last 

 generation upon the purchase of plant food to supplement that 

 produced upon the farm and replace that sold oft" in the crops. 

 It has been a matter of great concern to those officially interested 

 in agriculture that New England agriculture is not self-main- 

 taining. That is, it has been necessary to look outside of its 

 borders for the supplies of plant food. Phosphoric acid is 

 found in abundance in this country. Various refuses furnish 

 large amounts of organic nitrogen. Mineral nitrogen in the 

 form of ammonia salts is obtained from coke plants and gas 

 works as a by-product. It is also obtained directly from the 

 air by synthesis. All of the nitrogen in the form of nitrate of 

 soda is, however, imported from South America. 



POTASH FOR 191 5. 



While ordinary farm manures carry some' potash, and such 

 materials as sea weed and wood ashes contain potash, the world's 

 usable supply of potash has come from the mines of Germany. 

 The fact that war might make the potash of Germany or the 

 nitrate of soda of South America outside of the reach of the 

 American farmer, has been a matter of great concern for years 

 to the leaders in agricultural thought. This fear is realized in 



