SOIL ACIDITY 361 



inactivity of certain bases, especially those which tend to- 

 wards soil alkalinity. These necessary bases may be rendered 

 inactive by absorption phenomena or may be actually lost 

 through leaching and cropping. The specific and usually de- 

 leterious influence of so-called soil acidity may be due to an 

 excessive hydrogen ion concentration or to toxic bases such 

 as aluminum, iron, and manganese, which become active when 

 ionic calcium and similar bases are lacking, thus encouraging 

 a hydrogen ion accumulation. It is not improbable that in 

 some cases the detrimental influence may be improper nutri- 

 tion, either due to a lack of calcium as a nutrient or as a syner- 

 gistic agent necessary for the absorption of other nutrients 

 by plants. These detrimental conditions are alleviated in 

 practice by the application of some form of lime. 



A number of different methods has been devised to ascer- 

 tain quantitatively the lime requirements of soils. They are 

 all more or less inaccurate. Moreover, the lime requirement 

 of a soil and the lime necessary for best plant growth on that 

 soil are not of necessity the same. Plants respond very differ- 

 ently to the diverse conditions that may develop in the various 

 acid soils and it is seldom necessary or practicable entirely to 

 neutralize a very acid soil in order to correct its deleterious 

 condition. While lime-requirement methods are valuable in 

 research, qualitative tests are sufficient in practice. The 

 amount of lime that should be applied is determined not only 

 by the degree and nature of the acidity but also by the char- 

 acter of the crops, the length of rotation, the system of fer- 

 tilization, and similar factors. At best the amount of lime 

 that should be applied to the acre is but an estimate based 

 on many conditions, of which acidity is one, A qualitative 

 test seems as satisfactory a basis for such an estimate as a 

 more carefully controlled quantitative determination. 



