AGRICULTURAL UTILIZATION OF ACID LANDS. 3 
It is also well known to farmers that, after a few years’ prelimi- 
nary culture in rye, potatoes, and buckwheat, virgin timberland with 
its humus-laden soil of a century’s accumulation from rotting leaves 
and roots will sometimes produce heavy crops of timothy, wheat, and 
clover for one or two generations. ‘The success of these crops shows 
that the soil has ceased to be acid. Again, when the store of humus 
derived from the forest has fimally been exhausted after long years 
of ceaseless cropping, these soils revert to a condition of acidity, when 
lime is regarded as necessary to further agricultural prosperity. 
What is this peculiarity of forest leaves by which they make the 
soil at one time acid, at another alkaline? It is worth while to con- 
sider this question, for its answer will throw new light on the prac- 
tice of agriculture. 
DECOMPOSITION OF LEAVES. 
A layer of freshly fallen leaves on bare ground, moistened by rain, 
begins at once to decompose. A brown liquid leaches out of the 
leaves into the underlying soil. This liquid is acid. If the soil itself 
is naturally acid, its acidity 1s increased by these leachings. If the 
soil is sand, neutral in chemical reaction, it is made acid by the 
leachings from the leaves. But if the soil is alkaline from the 
presence of carbonate of lime, as in the case of ordinary loam of 
high fertility, the acidity of the leaf water is neutralized and its 
brown matter is precipitated, forming a portion of the black humus 
of the soil. On such an alkaline soil leaves decay rapidly from 
beneath and form a black, mellow, and very fertile leaf mold in 
which all traces of leaf structure have disappeared. Under such con- 
ditions the layer of leaf litter is always thin, often not lasting 
through the summer, and the transition from leaves to underlying 
mold is abrupt. 
In sand, however, there is no such acid-neutralizing substance, and 
both soil and leaves remain in an acid condition unfavorable to 
complete decay. The next year a fresh fall of leaves brings a new 
accession of acidity, and the acid condition of the leaf litter becomes 
permanent. In a sandy oak or pie woods there is thus built up a 
tough mat of upland peat often several inches in thickness, com- 
posed of half-rotted leaves interlaced with the rootlets of trees and 
underbrush. Such peat mats are always acid, like ordinary bog peat. 
One might conclude from what has been said that leaves unless 
treated with lime would remain acid throughout the process of 
decomposition. ‘Such a conclusion, however, would be erroneous. 
Leaves when sufficiently decayed lose their acidity and of them- 
selves produce a black mold that is not merely neutral in reaction, 
but sometimes markedly alkaline. 
