ly 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]

CHAPTER IV

EVIDENCES OF ACIDITY

_Character of Vegetation._ The character of the original forests is
determined much by the lime-content, and the practical man, when buying
a farm, rates its productive power by the kinds of timber it has
produced. The black walnut, ash, shellbark hickory, black and white oak,
sturdily grown, evidence a soil rich in lime, while the pines, small
blackjack and post oaks, and the chestnut are at home in non-calcareous
soils. The latter class of lands gains nothing in lime as time passes,
and the timber continues to be a sure index, but in the former class the
surface soil may have lost enough lime to limit crop production
materially while the trees continue to find in the subsoil all that they
need. It does not follow that the land has gone down in value to the
naturally lime-deficient class, but its power to produce is impaired,
and will remain so until there has been restoration of its original
alkaline state.

_Sorrel and Plantain._ We determine quite surely the state of the soil
by observance of the vegetation that roots in the surface soil and the
immediate subsoil. Sorrel is a plant popularly associated with soil
acidity, but this is not through any dislike for lime. It has been
observed growing in the edge of a heap. Its presence suggests acidity
because it can thrive in a sour soil that will not produce plants of
value which on even terms could crowd t