134 THE BOOK OF WHEAT 



Denitrifying organisms thrive best in a soil at least slightly 

 organic, and so packed as to exclude the oxygen of the air. 

 The nitrifying bacteria are unable to develop in organic mat- 

 ter, but its presence to some extent is not fatal to them. The 

 presence of nitrogenous substances has a deleterious effect upon 

 the cultures of nitrifying bacteria, which seem to fix atmo- 

 spheric nitrogen only in the absence of plenty of nitrogen in 

 the soil, consequently little benefit is to be obtained from in- 

 oculating soils containing a good supply of nitrogen. Most of 

 the nitrifying germs seem to exist in the first foot of soil, 

 while few, if any, exist at a greater depth than 18 inches. 

 Other bacteria, such as those which change the sulphur and 

 the iron compounds, also exist in the soil. 



APPLIED FERTILIZERS. 



Need, Time and Application of Fertilizers. Nearly all wheat 

 land that is under continual cultivation, even if crop rotation 

 is practiced, yields larger returns when fertilizers are properly 

 used. In each individual case local conditions and the economic 

 position of the wheat grower must determine to what extent it 

 is advantageous to fertilize. Each farmer must, in a large 

 measure, learn by experience whether the application of a cer- 

 tain fertilizer is profitable under his circumstances. It is now 

 well known that yield does not increase in proportion to the 

 amount of plant food applied, and that the increase in straw 

 is greater than that in grain. In determining the value of such 

 application, it must, of course, be remembered that more than 

 one crop is benefited. The wheat crop may be increased either 

 by direct fertilizing or by the residual effect of fertilizers ap- 

 plied to other crops in the rotation. The composition and 

 condition of the soil determine the relative importance of dif- 

 ferent fertilizing constituents. Phosphoric acid used alone 

 generally increases the yield of wheat grown anywhere on the 

 glacial drift area of the United States. 1 Either nitrogen or 

 potash applied alone does not seem to increase the yield great- 

 ly, while the application of both with phosphoric acid gives the 

 greatest gain. A fertilizer that can usually be found on the 

 market is one containing 4 per cent each of ammonia and potash 

 1 Hunt, Cereals in Amer, (1904), p. 75 



