Mar. i,i92i Relation of Calcium Content to Soil Reaction 861 



CALCIUM CONTENT OF SOILS STUDIED 



The soils of highest calcium content are found in group I. The four 

 soils in group I which have as low calcium content as several of the soils 

 in group II, or lower, are from the drier portion of the State. The soils in 

 group III have an average lower calcium content than the soils in groups 

 I and II. In general, the soils of a high calcium content have a more 

 alkaline reaction than soils of low calcium content; yet because of the 

 exceptions, the calcium content alone can not serve as the basis of classi- 

 fication as acid or alkaline. Most of the soils in group I are from the sec- 

 tion of the State where acid soils are not usually found, whereas most of 

 the soils from group III are from the section of the State where acid soils 

 are more common. Sandstone-derived soils from the drier portions of the 

 State may have a comparatively small amount of calcium and yet have 

 an alkaline reaction. 



In soils of high calcium content a larger percentage of the amount pres- 

 ent is soluble in acid than in soils of low calcium content. As the per- 

 centage of total calcium decreases, it is relatively less soluble. This is 

 true in comparing the groups and in comparing soils within groups. In 

 group I the proportion of acid-soluble calcium is greater than in group II, 

 and in group II it is greater than in group III. 



The differences in the amounts of calcium in forms soluble in Nji hy- 

 drochloric acid and in A// 5 hydrochloric acid are small. For practical 

 purposes they are of equal value. 



The pronounced differences between the amounts of calcium soluble in 

 hydrochloric acid and the total, especially in soils of low calcium content, 

 raises the question of the relative importance of determining the total 

 calcium in a soil or determining the amount soluble in cold dilute hydro- 

 chloric acid. These figures would indicate that the results obtained by 

 the acid digestion are more valuable. In soils of low calcium content, it 

 is present mostly in insoluble forms. While weathering gradually con- 

 verts this calcium into forms that are soluble, the amount of available 

 calcium obtained is insufficient for the needs of the soil. Such soils are 

 deficient in "agricultural lime." 



The figures for percentage of carbon dioxid show that all the soils in 

 group I have some carbonates, that only 6 of the 14 soils in group II have 

 carbonates in larger amounts than traces, and that only 3 of the soils in 

 group III have carbonates in larger amounts than traces and in these the 

 amounts are very small. 



RESULTS OF ELECTROMETRIC MEASUREMENTS 



The results on the electrometric measurements found in Table II are 

 arranged according to decreasing alkalinity values or, which means the 

 same thing, increasing acidity values. The figures expressing cubic cen- 

 timeters of calcium hvdroxid under the different P H values in each case 



