GROUND LIMESTONE
_Variation in Quality._ Limestones vary widely in purity. They were
formed under water, and clay and sand were laid down with the lime in
such quantity in some cases that the resulting stone is not worth
handling for soil improvement. A stone that is practically all carbonate
of calcium, or a combination of calcium and magnesium, is wanted because
it is these two elements that give value to the material. If a poor
stone is used, too much waste matter must be handled. Twenty-five per
cent more ground limestone of 80% purity must be applied than would be
required in the case of an absolutely pure limestone. Any stone above
90% pure in carbonate of lime and magnesia is rated as good, but the
best stone runs from 96% to 99%.
Limestones vary greatly in ability to resist disintegration, and this
variation is a big factor in determining the agricultural value of
ground limestone that has not been reduced to a fine powder. Particles
of a hard limestone may lie inert in the soil for many years. Hardness
also affects the cost of grinding.
_A Matter of Distribution._ Nature has used various agencies in reducing
limestone for the making of soils. The stone contained its lime in
carbonate form, and when reduced to good physical condition for
distribution it helped to make highly productive land. We know that lime
carbonate does the needed work in the soil so far as correction of
acidity is concerned, but in the form of blocks of limestone it has no
particular value to the land. Burning and slaking afforded to man a
natural means of putting it into form for distribution, and it is only
within recent years that the pulverization of limestone for land has
become a business of considerable magnitude. The ground limestone used
on land continues to be in part a by-product of the preparation of
limestone for the manufacture of steel, glass, etc., and the making of
roads, the fine dust being screened out for agricultural purposes. These
sources of supply are very inadequate, and too remote from much land
that requires treatment. Large plants have been established in various
parts of the country for the purpose of crushing limestone for use on
land, and quite recently low-priced pulverizers for farm use have come
upon the market and are meeting a wide need.
_Low-Priced Pulverizers._ A serious drawback to the liming of land is
the transportation charge that must be paid where no available stone can
be found in the region. Great areas do have some beds that should be
used, and a low-priced machine for pulverizing it is the solution of the
problem. Such a machine must be durable, have ability to crush the stone
to the desired fineness and be offered at a price that does not seem
prohibitive to a farmer who would meet the demands of a small farming
community. In this way freight charges are escaped, and a long and
costly haul from a railway point is made unnecessary. The limestone of
the locality will be made available more and more by means of this type
of machine, and the inducement to correct the acidity of soils will be
given to tens of thousands of land-owners who would not find it feasible
to pay freight and cartage on supplies coming a long distance. There
should be a market many times greater than now exists for the product
of all large plants, while the number of small pulverizers multiplies
rapidly. The very large areas that have no limestone at hand must
continue to buy from manufacturers equipped to supply them, and farmers
within a zone of small freight charges should be able to buy from such
manufacturers more cheaply than they could pulverize stone on their own
farms.
An individual, or a group of farmers, will buy a machine for pulverizing
limestone at a cost of a few hundred dollars when costly equipment would
be out of the question. If he has a bed of limestone of fair quality,
and the soil of the region is lacking in lime, an efficient grinder or
pulverizer solves the problem and makes prosperity possible to the
region. Within the last few years much headway has been made in
perfecting such machines, and their manufacturers have them on the
market. Any type should be bought only after a test that shows capacity
per hour and degree of fineness of the product. As a high degree of
fineness is at the expense of power or time, and as the transportation
charge on the product to the farm is small, there is no requirement for
the fineness wanted in a high-priced article that must be used
sparingly.
The aim should be to store in the soil for a term of years, and the
coarse portion is preferable to the fine for this purpose because it
will not leach out. The heavy application will furnish enough fine stuff
to take care of present acidity. If nearly all the product of such a
pulverizer will pass through a 10-mesh screen, and the amount applied is
double that of very fine limestone, it should give immediate results and
continue effective nearly twice as long as the half amount of finer
material. There could hardly be a practical solution of the liming
problem for many regions without the development of such devices for
preparing limestone for distribution, and it is a matter of
congratulation that some manufacturers have awakened to the market
possibilities our country affords.