﻿AGRICULTURAL UTILIZATION OF ACID LANDS. 5 



Table 111. — Acidity of green-manure crops to the acre, in term* of Ume require- 

 ment per acre. 





Crop. 



\cidity. 





Crop. 



Acidity. 



\if;llf:l 



Tons. 

 13 

 9 

 10 



Bye 



Tons. 



11 





Broom sedge. 





11 













The excessive acidity of these green manures at the time they are 

 first plowed under may be more clearly appreciated when one consid- 

 ers that the application of 2 to 3 tons of ground limestone per acre 

 usually satisfies the requirements of an ordinary acid soil. The 

 initial acidity of these green manures is thus shown to be several 

 times that of an equal bulk of ordinary acid soil. In the process of 

 decomposition, however, green manures, like the leaves already de- 

 scribed, tend to pass from an acid to an alkaline state, but at rates 

 which have not yet been determined. 



The lime requirement of green manures as given in Table III 

 must not be understood as the amount of lime actually required to 

 neutralize the acidity of a crop of these plants when plowed under. 

 A compact 6-inch layer of green manure would never be used in actual 

 practice, but a much smaller amount, as estimated in Table IV. This 

 table gives the estimated weight of the dry crop per acre, roots as well 

 as tops ; the amount of lime in the crop, expressed in terms of ground 

 limestone; and the acidity, in terms of the additional amount of 

 ground limestone required to neutralize the initial acidity. 



Table IV. — Weight, lime content, and acidity of green manures to the acre. 



Crop. 



Weight. 



Lime content. 



Acidity, expressed 

 as lime require- 

 ment. 



Alfalfa 



Red clover... 



Cowpea 



Rye 



Broom sedge 



Tons. 



Pounds. 



139 

 131 

 92 



11 

 4 



Pounds. 



267 

 142 

 200 

 178 



INJURIOUS EFFECTS OF ACIDITY. 



Although science can not be said to have demonstrated the full 

 details of the various ways in which ordinary crops are injured by 

 soil acidity, there is known to be one important chemical process 

 which is suspended under acid conditions, namely, the transforma- 

 tion of " unavailable " nitrogen into the form of nitrates. The 

 nitrifying bacteria do not thrive in acid media. In consequence, 

 those crops that require their nitrogen in the form of nitrates suffer 



