SOILS 293 



ment is the most reliable way of determining what 

 additions should be made to the land in the form of fer- 

 tilizers. 



Barnyard manure and growing plants plowed under 

 are the best kinds of fertilizers (Figure 252). 



FIG. 252. Results Obtained from Using Different Fertilizers. 

 Barnyard manure Unfertilized 



History tells us that the Indians used a fish in each 

 hill of corn to fertilize it. 



Commercial fertilizers usually contain nitrogen, potash, 

 and phosphoric acid. Lime in its ordinary form is also 

 used. 



Nitrogen as a Fertilizer. Nitrogen is a necessary plant 

 food. It may be applied to the soil as barnyard manure, 

 sodium nitrate, ammonium sulphate, potassium nitrate, 

 slaughter-house refuse, cotton-seed and linseed-oil meal, 

 and other forms of plant refuse. The most common form 

 in which nitrogen is sold as a commercial fertilizer is Chile 

 saltpeter or sodium nitrate. It contains about 16 per 

 cent of nitrogen. 



