PERMANENT AGRICULTURE 333 



in the amount named. To cut the hay and sell it from the 

 farm, however, would give a far different result. In this 

 case, little or no nitrogen would be added to the soil by the 

 legume since the amount contained in the roots and stubble 

 is usually about the same as that which these plants have 

 actually drawn from the soil itself ; but on the other hand 

 the land would lose heavily in phosphorus and potassium, 

 owing to the fact that legumes take large amounts of these 

 elements from the soil. 



By the appUcation of barnyard manure, not only nitro- 

 gen, but also phosphorus and potassium may be added to 

 the soil. A ton of ordinary barnyard manure contains 

 about ten pounds of nitrogen, two pounds of phosphorus 

 and eight pounds of potassium. If we compare these 

 figures with the amounts of the same elements removed 

 from an acre of ground by a fifty-bushel crop of corn, we 

 see that it would require the apphcation of about five 

 tons of manure per acre to replace the nitrogen removed 

 by a single corn crop. 



The use of commercial fertilizers to restore nitrogen 

 to the soil is much more general in the older sections of 

 our country than in the newer parts where the virgin 

 fertiUty has not been altogether exhausted and where the 

 clovers may be more easily grown. The fertilizers which 

 are commonly used to add nitrogen to the soil, are as fol- 

 Ipws: 



Sodium nitrate, called also Chile saltpeter. Each 

 hundred pounds of this product contains from fifteen to 

 sixteen pounds of nitrogen. It should be applied to the 

 land after plants have begun to grow, as it dissolves readily 

 and is soon leached or washed out of the soil. It should 

 be mixed with three or four times its weight of soil, as 

 otherwise it may injure the growing plants. The amount 

 used varies from one hundred to two hundred pounds 



