FRESH BURNED LIME
_An Old Practice._ The beneficial effect of caustic lime on land is
mentioned in some ancient writings. Burning and slaking afforded the
only known method of reducing stone for use in sour soils. Lime in this
form not only is an effective agent for correcting soil acidity, but it
improves the physical condition of tough and intractable clays,
rendering them more friable and easy of tillage. Caustic lime also
renders the organic matter in the soil more quickly available, an
increase in yield quickly following an application. These three effects
of burned lime brought it into favor, and a rational use would have
continued it in favor.
_Irrational Use._ The ability of caustic lime to improve the physical
condition of land and to make inert plant food available has led many
farmers to treat it as a substitute for manure, sods and commercial
fertilizers. Immoderate use gave increased crop yields for a time, and
the inference was easy that lime could displace the old sources of
plant food supplies. It became the custom in some regions to apply 200
to 300 bushels per acre to stiff limestone soils that had no lime
deficiency, as a test for acidity would have shown. The lime not only
made some mineral plant available, but it attacked the organic matter of
the soil, making it ready for immediate use and leaving the land
deficient in humus. Wherever stable manure and clover sods were not
freely used, the heavy application of caustic lime was followed
ultimately by decline in productive power. Such practice has come under
the condemnation of people who have not seen that the ill results have
no relation to the rational use of lime.
_What Lime Is._ There is abundant evidence that pulverized limestone, or
lime marl, or oystershell, or any other form of carbonate of lime,
corrects soil acidity and helps to make a soil productive. It is good,
no matter whether nature mixed the lime carbonate with clay, etc., to
make a choice limestone soil, or man applied it. Fresh burned lime is
only the stone after some worthless matter has been driven off by use of
heat. The limestone, carbonate of lime, is represented by the formula
CaCO_3. When heat is applied under right conditions the carbon dioxide,
CO_2, is driven off, and there remains CaO, which is calcium oxide,
called fresh burned lime.
If there were 100 pounds of the stone, and it was absolutely pure, 44
pounds would escape in form of the carbon dioxide, which had no value,
and 56 pounds would remain. The 56 pounds calcium oxide, or fresh burned
lime, have the same power to correct acidity as this same material had
when it was bound up in the 100 pounds of limestone. The 44 pounds were
driven off by heat, while if the limestone had not been burned the 44
would have separated from the 56 pounds in an acid soil, leaving the
actual lime to do the needed work of correcting acidity.
_Affecting Physical Condition._ While burning the stone does not affect
the ability to correct acidity, it does increase the power to make a
stiff soil friable and to bind a sandy soil. No one may say how much
this power to influence soil texture is increased, but it is marked, and
when improved physical condition is the chief reason for applying lime,
there is no question that fresh burned material is to be preferred to
pulverized stone or marl, or any other carbonate form. A light
application is not markedly effective in this respect, and the chief use
for this purpose has been in limestone areas that may not have had any
lime deficiency, but did have a stiff soil. The presence of the stone in
great quantity for burning on the farm made heavy applications possible.
_Using Up Organic Matter._ The presence of carbonate of lime in the form
of pulverized limestone or marl favors the disintegration of any organic
matter, but the action is so slow that it may not be observed. While the
use of limestone in manure piles is inadvisable for this reason, the
loss is not comparable to that resulting from mixing caustic lime with
manure. The caustic lime in a soil hastens decay of vegetable matter in
a degree impossible to the limestone or marl. Irrational use of the
former has produced such destructive action in many instances that the
failure to add manure or heavy sods for a long term of years has led to
heavy decline in producing power.
We are naturally so lacking in judicial temper that opinion has swung
violently from favor to disfavor. As most soils need organic matter, we
seize upon the thought that anything evidently inclined to use it up is
an evil. The purpose of tillage is in no small degree to bring about
disintegration and resulting exhaustion of vegetable matter. The latter
is a storehouse of plant food, and some of it is needed to feed the crop
desired. Tillage is no more to be commended for this purpose than a
quantity of lime equivalent in power to do the needed work. Excepting
the case of raw soils rich in the remains of plants, most land hardly
needs lime for this purpose, it may be, the tillage required for making
a seed bed retentive of moisture and for control of weeds being
effective, but the point is emphasized that the disintegration of
organic matter into available plant food is one of the chief aims of a
good farmer. It is only the excessive use of caustic lime that causes
loss.
The use of caustic lime in sufficient amount to correct all acidity, and
the use of such material to free plant food in humus sufficiently to
produce heavy sods, are just as good farm practices as drainage and the
application of manure.
[Illustration: Laying Foundation for a Lime Stack at the Pennsylvania
Experiment Station]
[Illustration: A Stack Nearly Completed at the Pennsylvania Experiment
Station]