STORING LIME IN THE SOIL
_Liberal Use of Limestone._ Land never does its best when skimped in any
way. As we raise the percentage of carbonate of lime in land that
naturally is deficient, we give increasing ability to such land to take
on some of the desirable characteristics of a limestone soil. It is poor
business to be making a hand-to-mouth fight against a state of actual
acidity unless the cost of more liberal treatment is prohibitive. The
most satisfactory liming is done where the expense is light enough to
justify the free use of material. When this is the case, extreme
fineness of all the stone is undesirable. There is the added cost due to
such fineness and no gain if the finer portion is sufficient to correct
the acidity, and the coarser particles disintegrate as rapidly as needed
in later years.
_Loss by Leaching._ Another valid argument against extreme fineness of
the stone used in liberal applications is the danger of loss by
leaching. Soils are so variable in their ability to hold what may be
given them that it is idle to offer any estimate on this point. The
amount of lime found in the drainage waters of limestone land teaches no
lesson of value for other land, the excessive loss in the former case
being due oftentimes to erosion that creates channels through the
subsoil, through which soil and lime pass.
[Illustration: A Limestone Pulverizer for Farm Use (Courtesy of the
Jeffrey Manufacturing Company, Columbus, Ohio)]
[Illustration: A Lime Pulver in Operation (Courtesy of the Jeffrey
Manufacturing Company)]
But we do know the tendency of lime to get away, and the use of several
tons of fine stone per acre may easily be followed by loss in many types
of soil. It is wholly reasonable to believe that some portion of such an
application should be coarse enough to stay where put until needed by
exhaustion of the finer portion. It is upon this theory that coarser
material often is preferred to the very finest.
_What Degree of Fineness?_ Assuming that the farmer is in a position to
store some carbonate of lime in his land for future use, giving the soil
an alkaline character for five or 10 years, the degree of fineness of
the stone is important, partly because there will be distinct loss by
leaching from many types of soils if all the material is fine as dust,
and specially because less finely pulverized material can be supplied
him at a lower price per ton. Much by-product in the manufacture of
coarse limestone for other purposes contains a considerable percentage
of material that would not pass through a 60-, or 40-, or 10-mesh
screen, but it does contain a big percentage of immediately available
lime, and a more complete pulverization of this by-product would add
greatly to its cost.
It is quite possible that a ton of such stone may be bought at a price
that would cover the value only of the fine portion, estimated on the
basis of the prevailing price of finely ground material, the coarse
material being obtained without any cost at all. It is this situation,
or an approach to it, that leads some authorities to become strenuous
advocates of the use of coarsely pulverized stone. The advice is right
for those who are in a position to accept it. If the money available for
liming an acre of land can buy all the fine stone needed for the present
and some coarser stone mixed with it for later use by the soil, the
purchase is much more rational than the investment of the same amount of
money in very fine stone that has no admixture of coarser material. If
the investment in the former case is larger than in the latter, it
continues to be good business up to a certain point, and the room for
some uncertainty is wide enough to provide for much difference in
judgment.
_Quality of the Stone._ Another factor of uncertainty is the hardness of
the stone. A limestone may have such flinty characteristics that a piece
barely able to pass through a 10-mesh screen will not disintegrate in
the soil for years, and there are other types of limestone that go into
pieces rapidly. The variation in quality of stone accounts for no little
difference in opinion that is based upon limited observation.
_Using One's Judgment._ It is evident that no hard and fast rule
respecting fineness may be laid down, and yet a rather definite basis
for judgment is needed. There is much good experience to justify the
requirement that when all ground lime is high-priced in any section for
any reason, and the amount applied per acre is thereby restricted, the
material should be able to pass through a screen having 60 wires to the
linear inch, and that the greater part should be much finer. Usually
some part of such stone will pass through a 200-mesh screen. When a
limestone on the market will not meet this test, some concession in
price should be expected. If the stone is not very flinty, a 40-mesh
screen may be regarded as affording a reasonably satisfactory test.
An increasing percentage of coarser material makes necessary an increase
in amount to meet the lime deficiency, and a distinct concession in
price is to be expected when a 10-mesh screen is used in testing. At the
same time a careful buyer will use a 60-mesh screen to determine the
percentage that probably has availability for the immediate future. A
coarsely ground article, containing any considerable percentage that
will not pass through a 10-mesh screen, must sell at a price justifying
an application sufficient to meet the need of the soil for a long term
of years, as the greater part has no immediate availability, and only a
heavy application can provide a good supply for immediate need.
_New York State Experience._ A bulletin of the New York agricultural
experiment station, published early in 1917, calls attention to the
rapid increase in demand for ground limestone in New York. Within the
last five years the number of grinding plants within the state had
increased from one to 56, and more than a dozen outside plants are
shipping extensively into the state. The bulletin says: "Farmers who
have had experience with the use of ground limestone are as a rule
satisfied with only a reasonable degree of fineness, and are able to
judge the material by inspection. When limestone is ground so the entire
product will pass a 10-mesh (or 2 mm.) sieve, the greater part of it
will be finer than a 40-mesh (or 1/2 mm.) sieve.... There are now in
operation in this State more than a dozen small portable community
grinders; they are doing much to help solve the ground limestone problem
and their use is rapidly increasing. In the practical operation of these
machines they grind only to medium fineness (2 mm.). To insist upon
extreme fineness is to discourage their use."
This State experiment station is only one of many scientific authorities
approving the use of limestone reduced only to such fineness that it
will pass through a 10-mesh screen, the cost of the grinding being
sufficiently small to permit heavy applications.