CHAPTER X 



RELATION OF ALKALI TO BIOLOGICAL 

 CONDITIONS IN THE SOIL 



THE effect of soil alkali in reducing the growth of crops 

 or in changing completely the type of native vegetation is 

 easily recognized. There are, however, equally as im- 

 portant changes produced in the microorganisms. These 

 changes cannot be detected without special study of a 

 technical nature and are therefore not so well understood. 

 The micro-flora of the soil is probably as varied and as 

 complex as the plant growth on the surface, but the re- 

 sponse of these smaller organisms has not been as thoroughly 

 studied as that of the higher plants. However, a few 

 rather definite facts have been established. 



Relation of Soil Organisms to Fertility. It has long 

 been known that bacteria and fungi in the soil are essential 

 to continued growth of the higher plants. The constant 

 tearing down of dead organic matter furnishes new material 

 for assimilation by living plants. Most plants require 

 nitrogen in the form of either ammonium salts or nitrate 

 nitrogen. One of the important sources of such salts is 

 vegetable matter of the soil which has been reduced to 

 the proper form by decomposition. Certain microorgan- 

 isms attack and break up the complex organic tissues of 

 plants as soon as their resistance has been decreased by 

 death or otherwise. Different organisms act on the dif- 

 ferent compounds as decomposition proceeds until the 

 material is finally reduced to the simple compounds such 



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