Mississippi valley is
restricted by lack of lime in the soil, and some states to the eastward
have one-half to nine-tenths of their acreage too low in lime for the
best results. Calcareous soils have been losing their distinctive
feature, and the immense areas of land naturally low in lime have
remained hampered in ability to make full returns for labor, fertilizer
and seed. It is this situation that brings the right use of lime on
land to the front as a matter of fundamental importance to the farmer.

_Causes of Soil Acidity._ If any discussion of the causes of soil
acidity would delay a decision to apply lime where needed, the time
given to such discussion would be worse than wasted. It is much more
important to be able to detect the presence of harmful acids and to
neutralize them than it is to know why the soil should be in such plight
that it could not supply the required lime and had become dependent upon
its owner for assistance. On the other hand, some of us find it
difficult to accept a fact without seeing a reason for it, and we may do
well to consider several causes that may be at work to put a soil out of
the alkaline class.

_Leaching._ One cause that appears obvious and easy of acceptance is
leaching. In the case of one Pennsylvania farm, lying in a limestone
valley, the lime had been washed out by action of water so freely that
caverns formed under the surface, and a test showed a marked deficiency
in the top soil. This land ceased to grow clover, and plantain and
sorrel abounded. This case, which is not an isolated one, showed an
unusually rapid loss, but we always expect to find the water from wells
and springs in a limestone country strongly impregnated with lime.
Drainage waters contain it. The draft by action of water is continuous,
and in some types could easily account for sufficient loss to change the
nature of the soil. We may place undue emphasis upon this factor, as
other causes are at work, but leaching is a leading source of loss.

_Chemical Compounds._ A serious cause of lime exhaustion that is being
studied by soil chemists is the presence of compounds in the soil that
combine with the lime and rob it of ability to serve the soil when new
acids form. The practical farmer accepts the statements of the chemists
on this point, and probably would not have his interests served by any
exact knowledge of the nature of these agents.

_Decaying Vegetation._ A cause of acid conditions that is wide