stiff limestone soils to make them friable, and to
make their plant food available, led to disuse of all lime in some
sections on account of the exhaustion that followed dependence upon
these large amounts as a manure. Queerly enough, these original
limestone soils have latterly been going into the acid class through
loss of their distinctive elements, and they, too, have become dependent
upon means for the correction of acidity.

CHAPTER III

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