SOIL ACIDITY 357 



samples are brought to dryness over a steam bath, and then 

 taken up with about 100 cubic centimeters of water. The 

 samples, after shaking, are allowed to settle, and the super- 

 natant liquid is treated with phenolphthalein. By the use 

 of a number of samples with varying amounts of lime-water, 

 the amount of the reagent necessary to neutralize the soil can 

 be approximately determined. 



The objections that can be urged against the Veitch method 

 may serve to indicate the difficulties that are in general en- 

 countered in using most of the methods for determining the 

 lime requirement of soils. The method is, in the first place, 

 very artificial, there being no assurance that the amount of 

 calcium absorbed is the same as that necessary to neutralize 

 the soil under field conditions. In the second place, it is 

 subject to considerable error. Even with the most careful 

 manipulation, the method is hardly accurate within 300 

 pounds of calcium oxide to the acre. 



If the results from such a method are to be applied directly 

 to practical liming it must be assumed that the amount of lime 

 necessary to neutralize an acid soil is the same as that capable 

 of alleviating the acidity for a particular crop. In light 

 of the variable influences of acidity on plants, this is an un- 

 scientific assumption to say the least. Acidity itself is too 

 intangible a condition. Moreover, it is in many cases not only 

 inadvisable but also unprofitable to satisfy the full lime re- 

 quirement of a soil. Some crops are unharmed or may even 

 be benefited by moderate acidity. The selection of a lawn 

 grass, for example, which is tolerant to acidity may allow 

 the suppression of certain troublesome weeds that would 

 spring up if the soil was limed. 



Since the results from lime-requirement methods must be 

 so radically modified to suit field conditions, they seem but 

 little better in a practical way than qualitative tests, which 

 distinguish only in a general manner between different de- 

 grees of acidity. The rapidity and simplicity of qualitative 



