STUDIES ON ACTI^'E BASES AND EXCESS AGIDS IN 



MINERAL SOILS* 



Technical Bulletin No. 57 



BY C. H. SPURWAY 



INTRODUCTION 



In 1917 the author published a short article (Spurway 9) showing a 

 relationship between the proportion of calcium to iron and aluminum 

 soluble in 0.2 IICl and the soil reaction. Acid soils gave proportions 

 of CaO : Fe„0:5 -f ALO3 above 1 : 1.3 and alkaline soils proportions be- 

 low this figure. These results indicate that soil calcium is the principal 

 element contributing to the basicity of soils and that the iron and 

 aluminum are concerned with soil acidity; that is, in combination as a 

 portion of the acid radical of soil salts. In a subsequent publication 

 (Spurway 8) it was shown that the quantity fixation of cations of 

 neutral salts by soils depended upon the quantity of soil bases in a 

 condition to react with the neutral salts. Also, that anions of chemical 

 salts were fixed by soils when they formed insoluble compounds with 

 soil bases. Pursuing the general problem effects of fertilizer salts on 

 soils, it was considered advisable to devise methods for determination 

 of active soil bases and acids, if possible, in order to define more closely 

 the reactions between soils and fertilizers on a quantity basis, as well 

 as the effects produced by fertilizers on the composition and reaction of 

 soils. 



As it is known that soil materials may be classified as partly active 

 and partly inert, and that the active substances of soils are largely 

 in an insoluble condition ; and also, that the hydrogen electrode may be 

 used to determine the neutralizing values of solids, it was assumed that 

 the hydrogen electrode could be of value in determining the neutralizing 

 value of soils for acids and bases, and hence the basicity and acidity of 

 soils on a quantitative basis. 



Attention is here called to the use of the term active bases in this 

 publication, which is intended to mean soil bases neutralized by acids 

 excepting iron and aluminum. 



•Presented to the Director for publication July 19, 1922. 



