CHAPTER XIII 



SOIL ACIDITY AINTD LIMING IN RELATION TO FERTILITY 



Soil Acidity Explained. — ^Many soils in humid regions are sour 

 or acid in character, because they manifest certain chemical 

 properties similar to acids. For example, an acid soil when 

 sufficiently moistened with pure, distilled water, turns blue litmus 

 paper^ red just as vinegar does, or the juice of an orange. This 

 condition is commonly spoken of as ^'soil acidity." 



Soil Acidity Lowers Fertility. — Soil acidity is harmful in several 

 ways: (a) It causes a lack of available calcium (Ca) to meet the 

 demands of crops like alfalfa and clover; (6) it renders the plant- 

 food elements less available; (c) it favors the development of 

 malnutrition diseases, especially of truck crops; (d) it causes 

 soils to be less responsive to fertilizer and manure treatments, and 

 (e) it favors the growth of certain weeds. It is important, there- 

 fore, that soil acidity be corrected to increase productiveness. 



Liming Defined. — The only economic way to correct soil 

 acidity is through liming. This means the application of neutraliz- 

 ing substances containing lime (CaO). In popular language 

 '^agricultural lime'^ is a general name given these substances, 

 which may be either lime carbonates (CaO + carbon dioxide gas), 

 lump or burnt lime (CaO), or hydrated lime (CaO + water). 

 Whenever any such material is mixed in an acid soil, there begins 

 at once a chemical reaction between the ''lime" added and the 

 soil, resulting in a disappearance of the acid conditions if a sufficient 

 amount be applied. 



How Liming Improves Acid Soils. — Liming may improve 

 acid soils in several ways: (a) Available calcium is added; (6) 

 acidity and certain poisonous substances are neutralized, thus 

 creating an environment much more favorable to the growth and 

 activity of the helpful soil bacteria, and to the growth of tender 

 roots; (c) plant-food elements in soils are rendered more available; 

 (d) greater returns are secured from f ertihzation ; (e) the contin- 

 ued use of lime on acid clays and clay loams tends to improve their 



1 Blue litmus paper is paper saturated with blue litmus, and is commonly 

 used as an indicator for acids. Litmus is a dyestuff extracted from certain 

 lichens. It has the property of turning blue in an alkaline solution and red 

 in. an acid. 



229 



