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 the sorrel out. There is constant
competition among plants for food and water and space, and some of our
worst weeds are not strong competitors of clover and grass where soil
conditions are not unfavorable to the latter.
Blue grass, the clovers and timothy give a good account of themselves in
a contest with sorrel and plantain where lime is abundant. This does not
mean that the seeds of these weeds may not be so numerous that an
application of lime cannot cause the clover and grasses immediately to
take the ground to the exclusion of other plants, but it is true that
the crowding process will continue until the time comes in the crop
rotation that these weeds cease to be feared, and clean sods can be
made. It is the absence of lime that permits such weeds to maintain
their reputation for good fighting qualities.
[Illustration: Limed and Unlimed Ends of a Plot at the Ohio Experiment
Station]
[Illustration: Effect of Finely Pulverised Limestone on Clover in a Soil
Having a Lime Requirement of 5200 Pounds of Limestone per Acre at the
Pennsylvania Experiment Station]
_The Clovers._ Red clover can make growth in some soils that have a lime
deficiency. If all other conditions are favorable, the lime requirement
may exceed one-half a ton per acre of fresh burned lime and not affect
the clover adversely, but farm experience throughout the country has
demonstrated that when soil acidity is only slight and clover grows with
difficulty, an application rarely fails to favor the clover in a marked
degree. Experience has taught the land owners to fear soil acidity when
red clover does not thrive where formerly it made good growth.
The prevalence of alsike clover in a farming region is indicative of
lack of lime. This clover thrives in a calcareous soil, but is more
indifferent to a small lime supply than is the red clover. As red clover
seedings begin to fail, the alsike gains in popularity, and where a soil
is decidedly sour the alsike is most in evidence. The latter has less
value to the farmer, rooting nearer the surface of the soil, and making
less growth of top, but it has gained in favor with farmers as soil
acidity has increased.
_The Grasses._ Timothy is more resistant to acidity than red clover,
but often fails to make a heavy sod where the deficiency in lime is
marked. Rhode Island Bent, known as redtop, is less exacting, and where
it thrives to the exclusion of timothy, or is in evidence in grass
lands, the inference is fairly safe that a test would show that the soil
is sour.
_When Production Decreases._ It is not a matter of any moment to the
owner of a productive soil whether or not his soil would give an acid or
an alkaline reaction under test. Returns from his labor are
satisfactory. Some land in this class is not strictly alkaline. The man
most interested in the effects of lime applications is the one who is
not satisfied with yields. The tests for acidity have been so many
throughout our eastern and central states that the owner of land which
is not productive has reason for the presumption that its percentage of
lime is too low. There is danger of error, and a scientific test is
surer, but in most cases the land which has been reduced from a fertile
to an unproductive state has lost its alkaline nature.
_Naturally Thin Soils._ Nature may be prodigal in supplies of nearly all
the elements of plant food to land and yet skimp its supply of lime,
but naturally poor soils are quite surely in the acid class. The
exceptions in our humid region are not extensive. When improvement is
planned for, involving additions of organic matter and plant food, the
application of lime to correct acidity is the first requirement. If such
land could be given the characteristics of a limestone soil so far only
as the lime factor is concerned, the building up of fertility would be
relatively easy. Liming must form the foundation of a new order of
things. The ability to grow the clovers and to furnish rich vegetable
matter to the soil, which naturally is poor in humus, rests upon lime
application first, and then upon any supply of plant food that may
continue to be lacking.