SOUR SOILS
_Loss of Lime._ Nature made the value of land as a producer of food
utterly dependent upon the activity of lime, and at the same time gave
it some power to shirk its work. In a normal soil is a percentage of
lime that came from the disintegration of rock of the region or was
transported by action of water on a huge scale. Possibly rarely would it
be in insufficient amount to keep a soil in a condition friendly to
plant life, and to feed the plant, if it stayed where nature placed it
and kept in form available for the needs it was intended to meet. There
is land that always was notably deficient in this material, and there is
land that was known in the early history of the world's agriculture to
be "sour," but the troubles of our present day in the case of the
farming country in the humid region of the United States is less due to
any natural absolute shortage than to combination that destroys value
and to escape by action of water.
[Illustration: Clover and Timothy Unfertilized at the Pennsylvania
Experiment Station Yielded 2460 Pounds per Acre]
[Illustration: Clover and Timothy with Fertilizer alone at the
Pennsylvania Experiment Station Yielded 3900 Pounds per Acre]
_Prevalence of Acidity._ The results of experiment station and farm
tests are conclusive that the soils of the greater part of all the humid
region of the United States show lime deficiency. Formerly, acidity was
associated in our minds with wet, low-lying land, but within the last
twenty years we have learned that it prevails in light seashore sands
along the Atlantic shore, in clays, loams and shales stretching to the
Appalachian system of mountains, on top of mountain ranges and across
foothills to our central states, and through them in stretches to the
semi-arid lands of the west. While not all this land has fallen into the
lime-deficient class, and the great part of some states remains
alkaline, the tendency toward acidity is continuous.
Crop production in great portions of the 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 widely known
and accepted, and that may therefore stand out in our thinking with
undue prominence, is connected with the decay of green vegetable matter
in the soil. Many of us have seen fields rendered temporarily
unproductive by the plowing down of a mass of immature plants in
midsummer. All organic matter, indeed, in its decay makes a draft upon
the lime content of the soil in which it may be buried.
_Removal in Crops._ Lime is taken out of land by plants, and the loss is
a considerable item, but our interest is in the form of lime that can
correct soil acidity, and we know that compounds of lime that are
worthless for this purpose may be the chief source of the lime in our
crops. A determination of the lime in the ash of a crop does not give
data of much practical value.
[Illustration: Clover and Timothy with Lime Alone at the Pennsylvania
Experiment Station Yielded 4900 Pounds per Acre]
[Illustration: Clover and Timothy with Fertilizer and Lime at the
Pennsylvania Experiment Station Yielded 6290 Pounds per Acre]