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BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 



in the eastern United States alfalfa is not successful, except on 

 calcareous soils, unless the natural acidity of the soil has been neu- 

 tralized by suitable applications of lime. 



One result of this advocacy of lime has been that in our anxiety 

 to neutralize our acid soils and thus make them yield larger crops 

 of such staples as clover, timothy, wheat, and alfalfa we have neg- 

 lected to recognize clearly and to utilize the fact that some agri- 

 cultural plants thrive as well in an acid soil as in an alkaline soil, 

 or even better. It is proposed to discuss in this bulletin the bearing 

 of soil acidity on agriculture and to direct attention to the utilization 

 of part of our cheap acid lands through the development of rota- 

 tions in which all the crops are acid tolerant, and the cost of making 

 frequent and heavy applications of lime is therefore eliminated. 

 These considerations are especially pertinent in sections where lime 

 is expensive because of the remoteness of good commercial deposits 

 of limestone. Where lime is not expensive the use of applications 

 sufficiently heavy to neutralize the acidity of the soil is unques- 

 tionably profitable for many of the staple agricultural crops. 



SOURCE OF SOIL ACIDITY. 



One of the principal sources of soil acidity is deca}dng vegetation. 

 The fallen leaves that carpet the floor of a forest are exceedingly 

 acid. Freshly fallen leaves of some of our common trees show the 

 following degrees of acidity, expressed in tons of ground limestone 

 required per acre to neutralize a compact layer 6 inches in depth, 

 estimated to weigh when dry 500,000 pounds, one-fourth as much as 

 "ordinary soil. 1 



Table I. — Acidity of freshly fallen leaves, in terms of lime requirement per acre. 



Kind of leaves. 



Acidity. 



Kind of leaves. 



Acidity. 





Tons. 



25 

 16 

 22 





Tons. 



22 



Red oak 





14 





Virginia pine 



1 



22 







It is well known to farmers that on newly cleared timberland, not 

 burned over, most crops do not grow well at first. A few, however, 

 thrive in such situations, notably rye, buckwheat, and potatoes. All 

 these are known to be acid tolerant. Table I, although represent- 

 ing conditions of acidity in excess of that actually existing in a 

 cleared field, shows one of the sources of the acidity with which the 

 plants have to contend and which is fatal to crops that are not acid 

 tolerant. Another source of pronounced acidity in newly cleared 

 timber-lands is the freshly killed roots of the trees and underbrush. 



1 These acidity determinations were made by Mr. G. II. Baston, of the Bureau of Plant 

 Industry, using phenolphthalein as an indicator, after boiling off the carbon dioxid. 



