856 Journal of Agricultural Research voi.xx, no. « 



addition of rain or irrigation water temporarily reduces the concentration. 

 If some of the water is carried off in the drainage, it takes away a certain 

 amount of the dissolved salts. At the present time calcium is removed 

 from the soil more rapidly than any other base (5, p. 23). Lyon and 

 Bizzell (8) found in lysimeter experiments that the equivalent of 485 

 pounds of calcium carbonate per annum leached from some soils. The 

 continuous removal of calcium from the soil produces an unbalanced con- 

 dition known as lime deficiency or acid soil. When calcium carbonate 

 is added to the soil the balance is restored and the reaction is neutral or 

 slightly alkaline. 



The studies presented in this paper are not designed to settle any differ- 

 ences of opinion relative to the meaning of soil acidity nor to decide 

 which is the best method of determining the lime requirement of the soil. 

 They are presented as a contribution to the partial solution of a very com- 

 plex as well as important problem. The electrometric titration has been 

 used by a number of investigators (6, 9, 10). Because of its intrinsic 

 value it was used in this study of the relation between the calcium con- 

 tent of some typical Kansas soil and the reaction. 



MEANING OF SOIL ACIDITY 



The following is usually taken as the meaning of acidity in soil: Total 

 acidity means the total quantity of hydrogen ions which may be pro- 

 duced when the equilibrium is continually shifted by the introduction 

 of hydroxyl ions. The quantity of hydrogen ions present at any one 

 moment is regarded as the intensity of acidity. This definition would be 

 inclusive and very convenient if it were not for the adsorptive power of 

 colloids in soil. It will be shown that this intensity of acidity may be very 

 small as related to the total acidity. Understood in this way, quantita- 

 tively, total acidity has the same meaning as potential acidity. Poten- 

 tial acidity may be due to undissolved substances, or to soluble com- 

 pounds only partly hydrolyzed or dissociated. It appears also to be due 

 to colloidal clay; but whatever it is due to, the conditions are such that 

 as soon as more hydroxyl ions are introduced the equilibrium is shifted 

 by the production of more hydrogen ions. The absolute neutral point 

 obtains when the number of hydrogen ions and the number of hydroxyl 

 ions are equal and each has a concentration of io -7 per liter. 



SOILS USED IN THIS STUDY 



Twelve counties in Kansas have been surveyed and mapped by the 

 Bureau of Soils, United States Department of Agriculture. Five of these 

 counties were worked in cooperation with the Kansas Agricultural Ex- 

 periment Station. These types have been sampled and analyzed by the 

 Department of Chemistry, Kansas Agricultural Experiment Station 

 (1-4, 11). Determinations have been made for nitrogen, phosphorus, 

 potassium, carbon, carbon dioxid, and calcium. On the basis of these data 



