CHAPTER VIII 

 ACID SOILS AND ALKALI SOILS 



Some soils are termed acid, or sour soils. They are so 

 called because they give the same tests with certain chemi- 

 cals that are obtained with vinegar and other acids. A 

 common test for acids is to bring them in contact with blue 

 litmus paper, and if the material is acid the paper is colored 

 red. Soils that are strongly acid will also do this. Another 

 property of acid materials is that, if sufficient quick-lime 

 is brought in contact with them they will no longer color 

 blue litmus paper red. This may be tried by slowly stirring 

 quick-lime into vinegar and testing it occasionally with 

 litmus paper. If sufficient quick-lime be added to an acid 

 soil, it will no longer turn blue litmus paper red. 



Whether a soil is acid or not is a matter of practical im- 

 portance, because some plants do not grow so well on sour 

 soils as they do on soils that are neutral or alkaline ; on the 

 other hand some crops prefer an acid soil. 



133. Nature of soil acidity. — There are two kinds of 

 soil acidity (1) when acids are present that have been formed 

 by fermentation of organic matter in the soil, (2) when there 

 is a deficiency of such material as lime or potash. In either 

 case the soil will color blue litmus paper red. 



134. Positive acidity. — The condition of soil first men- 

 tioned above has been termed positive acidity. It arises 

 from the decomposition of organic matter when soil condi- 

 tions are not favorable to the proper breaking down of the 

 intermediate substances. An insufficient air supply caused 



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