﻿4 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 



CHANGE FROM ACIDITY TO ALKALINITY. 



The reason for this change from acidity to alkalinity lies primarily 

 in the chemical composition of the leaves. From the beginning 

 they are heavily charged with lime, as the following determinations 

 in Table II will show : * 



Table II. — Percentage of lime in freshly fallen leaves, in terms of calcium car- 

 bonate, or ground limestone. 



Kind of leaves. 



White oak.. 



Red oak 



Silver maple 



Percentage 

 of lime. 



1.12 

 3.08 

 3.31 



Kind of leaves. 



Sugar maple. 



Tulip tree 



Virginia pine 



Percentage 

 of lime. 



4.56 



5.06 



.16 



Soils containing such high percentages of lime as these leaves 

 would be markedly alkaline, yet the leaves, as shown by the table on 

 page 2, are strongly acid. It is evident from a consideration of both 

 facts that the lime existing in the fresh leaves has gone into combina- 

 tion with their acid substances to the full extent of its ability to neu- 

 tralize them, and that the acidity recorded on page 2 represents the 

 acid substances in the leaves in excess of the amount already neutral- 

 ized by the lime. 



As the decomposition of the leaves progresses these excess acid 

 substances are leached out or disorganized, the lime itself is released 

 from its combinations, and a stage is reached where the lime is more 

 than sufficient in amount to neutralize the remaining acidity. The 

 mass has become an alkaline leaf mold. This change from acidity to 

 alkalinity is often hastened by the development through bacteria of 

 ammonia or other substances having an alkaline reaction. 



The rapidity with which different kinds of leaves pass from the 

 acid to the alkaline stage varies exceedingly. Leaves of silver maple 

 in some tests have rotted so rapidly as to reach the alkaline state 

 within a year. Red-oak leaves remain acid for several years, and pine 

 leaves for many years. 



ACIDITY OF GREEN MANURES. 



Acidity determinations of several of the plants that are commonly 

 plowed under for green manure give the following results, expressed 

 in the weight of ground limestone that would be required per acre to 

 neutralize a compact layer 6 inches in thickness. 



1 These lime determinations were made by Mr. J. F. Breazoalo, of the Bureau of Chem- 

 istry, from duplicates of the same samples from which the acidity determinations on 

 page 2 were made. 



