JOURNAL OF MCUIHJML RESEARCH 
Vol. XXVI Washington, D. C., October 20, 1923 No 3 
SOIL REACTION IN RELATION TO CALCIUM ADSORP¬ 
TION 1 
By C. O. Swanson 2 
Professor of Agricultural Chemistry, Kansas State Agricultural College 
DISCUSSION OF TERMS AND STATEMENT OF THE PROBLEM 
SOIL REACTION AND LIME REQUIREMENT 
Various terms are found in soil literature relative to soil reaction. 
Soil acidity” often refers to the reaction of moist soil toward some 
indicator such as litmus or phenolphthalein. “Lime requirement” 
refers to the amount of a calcium compound necessary to change the 
reaction to some chosen standard, usually the color change of phenolph¬ 
thalein. The minimum amount of lime required to change the reaction 
to this standard is referred to as the “immediate lime requirement,” 
while “continuous lime requirement” is an expression of the amount 
of lime needed to keep the soil at the desirable reaction for a period of 
time. 
ACID, NEUTRAL, AND ALKALINE SOLUTIONS 
The large amount of work done in recent years on hydrogen-ion concen¬ 
tration has served to clarify the meaning of the terms acid, neutral, 
and alkaline. All aqueous solutions contain, no matter what else is 
present, hydrogen ions and hydroxyl ions. In a neutral solution the 
respective concentrations of these two ions are equal. In an acid solu¬ 
tion the hydrogen-ion concentration is in excess of the hydroxyl-ion 
concentration, while in an alkaline solution the reverse is true. These 
ideas of acidity, neutrality, and alkalinity are applicable to water sus¬ 
pensions and water extracts of soil. 
THE EXPRESSION FOR SOIL REACTION 
In this paper the degree of soil reaction refers to the numerical value 
of the hydrogen-ion concentration as determined by the hydrogen 
electrode. This value can also, with certain restrictions, be determined 
by the use of indicators. Gillespie (14)* found that there was a fairly 
1 Accepted far publication July 18, 1923. Contribution No. 100 from the Department of Chemistry, 
Kansas Agricultural Experiment Station. Presented to the faculty of the graduate school of Cornell 
University, September, 1922, as a major thesis in partial fulfillment of the requirements for the degree of 
doctor of philosophy. . . , „ „ 
2 The writer desires to express his appreciation to Professors T. L. Lyon, J. A. Bizzell, and H. O. 
Buckman for helpful suggestions in doing this work and in preparing the thesis. 
3 Reference is made by number (italic) to “Literature cited,” p. 120-123. 
Journal of Agricultural Research, 
Washington, D. C. 
aha 
Vol. XXVI, No, 3 
Oct. 20, 1923 
Key No. Kans.-39 
60374—23-1 
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