) 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 decaying 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. 
TABLE I.—Acidity of freshly fallen leaves, in terms of lime requirement per acre. 
———_ 
Kind of leaves. : Acidity. Kind of leaves. Acidity. 
Tons. Tons. 
Wihitercakeme me aeee saan tee see oc ose 2511|¢ SU cara a plese sos eee eee 22 
LR OR e eee a tes i ye oe ae ana eae 16). Dulip trees 22. et eee 14 
Silversmapleeacsce ees ee eee aaa OP Migaiane), |e oasoewesaeaSse NER OEE 22 
ce 
Tt 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 
timberlands is the freshly killed roots of the trees and underbrush. 
1 These acidity determinations were made by Mr. G. H. Baston, of the Bureau of Plant 
Industry, using phenolphthalein as an indicator, after boiling off the carbon dioxid. 
