PRESS BULLETIN No. 78.
ilorida Agricullura Experimen l Slation.
MATERIALS FOR CORRECTING SOIL ACIDITY.
BY A. W. BLAIR.
It is becoming more evident every day that some material will have to be
used extensively to correct "sourness," or acidity, in Florida soils. Just
what.this material should be is not entirely clear in the minds of many who
are concerned. Quicklime, hydrated lime, air-slacked lime, and wood ashes,
have all been used, and have proved effective; though they are not equally
,effective, pound for pound. Finely ground limestone, marl, and basic slag-
sometimes called Thomas slag, or slag phosphate-have also been used to a
The different forms of lime have long been employed as correctives of
"sour" soils. They are, however, unpleasant to handle, and they may, under
some circumstances, cause injury to the soil or to the crop.
Caustic lime, or quicklime, especially, may cause an undue liberation of
plant food, and a too rapid burning out of the humus. If applied near the
time when the seed is sowil, or after the,plants are up, there is also a possi-
bility that injury may be done to these. If this form of lime is used, it
should be thoroughly worked into the soil some weeks, or even months, be-
fore the crop is planted.
Hydrated or water-slacked lime is not so likely to cause injury as quick-
lime; and if the proper amount of water has been added, it is not so un-
pleasant to handle. Seventy-four pounds of this would be equivalent to fifty-
six pounds of quicklime.
Air-slacked lime is less caustic than either of the other two forms, andl
on this account would perhaps be safer to use. It is formed by leaving
quicklime exposed to the air, and is a mixture of calcium hydrate (hydrated
'lime) and calcium carbonate. When quicklime is exposed to the air for a
-long time, so that it becomes thoroughly air-slacked, it attains the same
composition as limestone; in which case 100 pounds would be equivalent to
100 pounds of ground limestone, or to 56 pounds of quicklime.
LIMESTONE AND MARL.
Finely ground limestone is a more desirable material for correcting soil
acidity than any of the forms of lime mentioned above. It is effective, and
does not have the objectionable features which other forms have; that is,
it is not unpleasant to handle, and produces no caustic or burning effect; in
fact, there can hardly be any danger of applying too much. It does not, how-
ever, have the same neutralizing value as quicklime, 100 pounds being re-
quired where 56 pounds of quicklime ,would suffice. At present, ground
limestone would probably not be found upon the market, but when it is de-
.nianlded tnere is little doubt that some one would be ready to supply the
January~ 9, 1908.
want. There are a number of places throughout the State where limestone
may be procured, and the work of the State Geological Survey will unques-
tionably locate other deposits. Mills, such as are used for grinding phos-
phate rock, could be installed at one or more of these places according to
Marl and ground shells would also be effective materials for correcting
soil acidity, the effectiveness depending upon their quality and fineness.
A marl containing half as much calcium carbonate as a good quality of lime-
stone, would be just half as effective as the limestone; that is, it would be
necessary to apply just twice as much marl as limestone to get the same
ASHES AND SLAG.
Hardwood ashes will neutralize soil acids, and if unleached, will furnish
some potash; so that it is a good policy to save all that may be produced on
tne farm. If hardwood ashes must be bought, however, they would prove an
expensive material for this purpose. Limestone would be much cheaper.
The lime in a ton of good hardwood ashes would have about the same neu-
tralizing effect as half a ton of finely ground limestone; and a ton of such
ashes would probably cost $15 to $17. The value of the potash and phosphoric
acid in this ton would not exceed $5 to $7, making the cost of the lime-
which as stated above would be equivalent to half a ton of finely ground
limestone-$8 to $12. In Illinois the price of ground limestone in carload
lots, on board the cars, varies from 50c to $1 per ton, according to the fine-
ness. Certainly it should not cost more than double that amount in Florida.
Basic slag, or Thomas slag is a by-product in the manufacture of steel
from pig-iron containing phosphorus. It contains from 15 to 20 per cent.
of phosphoric acid and a large quantity of free lime, as well as some iron,
magnesia, etc. If it is desired to supply the soil with phosphoric acid, in ad-
dition to correcting the acidity, this material would be well adapted for the
purpose, if it can be had at a reasonable price; but if correcting acidity is
the only object in view, basic slag would be too expensive.
AMOUNTS TO USE.
In most cases where a corrective for "sour" soils is needed, it will be
safe to use from one-half to two tons of air-slacked lime, or from two to six
tons of finely ground limestone, per acre. If limestone is used it may be ap-
plied at any time, but if it can be worked into the soil some months before
the crop is planted, so much the better. It will then have more time to
attack the acids.
State papers please copy.