Part 2 (1/2)
_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, gla.s.s, 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 crus.h.i.+ng 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 coa.r.s.e 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 pa.s.s 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.
CHAPTER IX
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 coa.r.s.er 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 pa.s.s.
[Ill.u.s.tration: A Limestone Pulverizer for Farm Use (Courtesy of the Jeffrey Manufacturing Company, Columbus, Ohio)]
[Ill.u.s.tration: 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 coa.r.s.e enough to stay where put until needed by exhaustion of the finer portion. It is upon this theory that coa.r.s.er material often is preferred to the very finest.
_What Degree of Fineness?_ a.s.suming 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 coa.r.s.e limestone for other purposes contains a considerable percentage of material that would not pa.s.s 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 coa.r.s.e 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 coa.r.s.ely 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 coa.r.s.er 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 coa.r.s.er 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 pa.s.s 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 pa.s.s 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 pa.s.s 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 coa.r.s.er 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 coa.r.s.ely ground article, containing any considerable percentage that will not pa.s.s 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 s.h.i.+pping 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 pa.s.s 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 pa.s.s through a 10-mesh screen, the cost of the grinding being sufficiently small to permit heavy applications.
CHAPTER X
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 subst.i.tute 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 oystersh.e.l.l, 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.