280 ILLINOIS STATE ACADEMY OF SCIENCE 



A COMPARATIVE STUDY OF SOIL ACIDITY 

 METHODS ON ILLINOIS SOILS 



E. E. DeTurk and J. W. Coale, University of Illinois 



INTRODUCTION 



Much effort lias been spent by agricultural investiga- 

 tors in determining the so-called lime-requirement or 

 acidity of soils. That much of this effort is justified will 

 be conceded, when it is recognized that the major portion 

 of all agricultural land in the humid regions of the Uni- 

 ted States is "acid," and that on such lands the correc- 

 tion of this condition is fundamental to the establishment 

 and maintenance of crop production at a reasonably high 

 level. 



Under humid weathering conditions the decomposition 

 of soil minerals is accompanied by the liberation of basic 

 elements in the form of soluble compounds, largely 

 through the action of water and carbonic acid. The sol- 

 uble bases are removed, partly in the ground-water and, 

 in tilled soils, in the crops harvested from the land. The 

 continual removal of basic elements at a more rapid rate 

 than that at which the acidic elements are removed pro- 

 duces several conditions in the soil, which taken together, 

 make it an unfavorable substrate for the growth of many 

 of the most important farm crops. In soils which have 

 developed a very high degree of acidity, practically all 

 plants refuse to grow. Some of the more important fac- 

 tors of soil acidity may be enumerated as follows : 



(a) The presence of hydrogen-ions, indicating true 

 acidity in the chemical sense. 



(b) Insoluble acids and acid salts. 



(c) Colloids, both organic and inorganic, most of 

 which absorb basic ions, rather than acid. 



(d) Aluminum compounds which are either soluble or 

 in a combination sufficiently "active" as to be rendered 

 soluble by reaction with neutral salts, or to affect unfav- 

 orably the growth of plants. 



Each of these factors taken separately may not be 

 necessarily toxic to growing plants ; indeed corn, wheat, 

 rye and many other crops grow best in a soil containing 

 a low concentration of hydrogen-ions. However, since 



