ACID, OR SOUR, SOILS 379 



the soil in this way is very considerable. When the 

 vegetation on the land is returned to it after life 

 ceases and its organic material is again incorporated 

 with the soil, there is no loss in this way, but in ordi- 

 nary agricultural practices most of the above-ground 

 portion of the crops is removed from the land. The 

 manure of growing animals returns to the soil only a 

 small proportion of the calcium that was originally in 

 the plants. 



Breazeale and LeClerc ! found that the selective action 

 of plants in absorbing more bases than acids from a 

 nutrient solution caused the solution to become toxic to 

 wheat seedlings because of its acidity. 



286. Effect of green manures on acidity. — Although 

 the return of vegetation to the land on which it grew 

 does not result in any actual loss of basic material to 

 the soil, it generally results in the formation and libera- 

 tion of organic acids that unite with the basic material 

 and thus render it neutral. In soils deficient in lime 

 the incorporation of green-manure crops has been con- 

 sidered to temporarily produce an acid condition. 

 Coville 2 determined the acidity of some green-ma- 

 nure crops, on the basis of which he has estimated 

 the acidity, in terms of ground limestone required to 

 neutralize it, when the lime contained in the crop is de- 

 ducted from the total lime required. This is given in the 

 table on the next page. 



1 Breazeale, J. F., and LeClerc, J. A. The Growth of Wheat 

 Seedlings as Affected by Acid or Alkaline Conditions. U. S. 

 D. A., Bur. Chem., Bui. 149. 1912. 



2 Coville, J. V. The Agricultural Utilization of Acid Lands 

 by Means of Acid-Tolerant Crops. U. S. D. A., Bui. No. 6, 

 p. 5. 1913. 



