FERTILIZERS 35 



calcium, the supply of which is likely to become depleted 

 in ordinary soils unless care is taken to maintain them. In 

 the last lesson we learned that a 20-bushel yield of wheat 

 removed 22 lbs. of nitrogen, 4.1 lbs. of phosphorus and 5.8 

 lbs. of potassium. Nitrogen costs about 18 cents per pound, 

 phosphorus about 6 cents per pound and potassium about 

 6 cents per pound, when purchased in the form of com- 

 mercial fertilizers. To replace the elements removed by 

 20 bushels of wheat would cost at these prices about $4.55 

 or 22^ cents per bushel of wheat. If it were necessary 

 to purchase all these elements used, it would make a 

 very heavy tax on wheat raising. . 



Nitrogen is present in the air in very large quantities. 

 The farmer has a way at his command by which he can 

 gather this nitrogen and add it to the soil at practically 

 no cost. This is done by growing legumes, such as clover, 

 alfalfa, etc. (See Chapter VI ) A good rotation of crops 

 (See Chapter XXIII) in which clover or some other legume 

 crop is included one or more times in from three to seven 

 years will provide for the maintenance of a sufficient supply 

 of nitrogen. Barnyard manure also contains liberal amounts 

 of nitrogen and its application to the soil every few years 

 is very helpful in maintaining a supply of nitrogen. It is 

 not necessary, therefore, under ordinary farm conditions, 

 to purchase nitrogen. It is very important in connection 

 with the maintenance of nitrogen that a liberal supply of 

 vegetable matter be maintained. When it becomes neces- 

 sary to purchase nitrogen for a fertilizer, it may be secured 

 in the form of sodium nitrate, a product taken from mines, 

 ammonium sulphate, a by-product in the manufacture of 

 gas, dried blood and other by-products from large packing 

 plants or slaughter houses. 



Phosphorus. — It will be noted in the last lesson that 

 phosphorus is present in the soil in comparatively small 

 quantities. It is removed from the farm when either 

 grain or live stock is sold. The addition of manure adds 

 to the supply, especially if mill feed is purchased. Often 

 the elements of fertility may be more economically pur- 

 chased in the form of feed to be fed to live stock and the 

 manure appHed to the soil than to purchase them in the 



