SOIL ACIDITY 355 



Such methods may be divided, for convenience of discussion, 

 under two heads: quantitative determinations and qualita- 

 tive tests. In the first case the methods devised purport to 

 give the lime requirement of the soil. The second group of 

 methods attempts to determine whether the soil is acid and 

 may in addition give some general idea as to the degree of 

 acidity. 



191. Lime-requirement determinations. — A great num- 

 ber of methods has been advanced for the determination of the 

 lime requirement of soils. The methods may for convenience 

 be grouped under three heads: (1) those using a neutral salt, 1 

 (2) those utilizing a basic substance, 2 and (3) miscellaneous 

 procedures. 



In the first group, some neutral salt such as potassium ni- 

 trate is added to the soil and the amount of actual acidity 

 developed is determined under suitable control. The actual 

 acidity produced by selective absorption and basic exchange 

 is thus taken as a measurement of the soil acidity and is gen- 

 erally figured to pounds of lime to the acre. 



In the second group some basic substance, preferably that 

 which is used in practice to correct acidity, is added to the 

 soil. The amount of the basic substance necessary to render 

 the soil alkaline or neutral is determined in pounds to the 



1 The Hopkins methods utilize potassium nitrate or sodium chloride. 

 Calcium acetate is used in the Jones method. 



Hopkins, C. G., Knox, W. H., and Pettit, J. H., A Quantitative 

 Method for Determining the Acidity of Soils; U. S. Dept. Agr., Bur. 

 Chem., Bui. 73, pp. 114-121, 1903. 



Jones, C. H., Method for Determining the Lime Requirement of 

 Soils; Jour. Assoc. Off. Agr. Chemists, Vol. I, No. 1, pp. 43-44, 1915. 



2 The Veitch method utilizes calcium hydroxide, the Tacke method 

 calcium carbonate and the method proposed by Hutchinson and Mac- 

 Lennan calcium bicarbonate. 



Veitch, P. P., Comparison of the Methods for the Estimation of 

 Soil Acidity; Jour. Amer. Chem. Soc, Vol. 26, pp. 637-662, 1904. 



Tacke, Br., iioer die Bestimmung der freien Humussduren; Chem. 

 Ztg., Bd. 21, Heft. 20, S. 174-175, 1897. 



Hutchinson, H. B., and MacLennan, K., The Determination of the 

 Lime Requirement of the Soil; Chem. News, Vol. 110, p. 61, 1914. 



