_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.

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 quant.i.ty 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 quant.i.ty 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.

[Ill.u.s.tration: Laying Foundation for a Lime Stack at the Pennsylvania Experiment Station]

[Ill.u.s.tration: A Stack Nearly Completed at the Pennsylvania Experiment Station]

CHAPTER XI

BURNING LIME

_Methods of Burning._ Limestone contains the calcium and magnesium that must be the chief source of supply of American soils, though marls, ashes, etc., have their place. The burning of the stone has been the leading means of bringing it to a condition of availability to the soil, excepting, of course, the vast work of disintegration carried on through all the ages by nature. Pulverization of the rock by machinery for use on land is recent.

The devices for burning are various, a modern lime plant containing immense kilns, cylindrical in form, the stone being fed into them at the top continuously, and the lime removed at the bottom. A large part of the lime that is sold for use on land is made in plants of this kind.

Some is burned in kilns of cheap construction, but a traveler through a limestone country finds few such kilns now in use.

_The Farm Lime Heap._ A common method of producing lime for farm use has been, and continues to be, a simple and inexpensive one, involving the use only of wood, coal and limestone, with earth as a covering. Dr.

Wm. Frear, chemist of the Pennsylvania station, in Bulletin 261 of the Pennsylvania department of agriculture, describes a method of burning lime on the farm as follows: "A convenient oblong piece of ground is cleared, and leveled if need be, to secure a fit platform. Upon this level is placed a layer or two of good cord wood, better well seasoned, arranged in such manner as to afford horizontal draught pa.s.sages into the interior of the heap. Between the c.h.i.n.ks in the cord wood, shavings, straw or other light kindling is placed. The stone having been reduced to the size of a double fist, sometimes not so small, is laid upon the cord wood, care being taken to leave c.h.i.n.ks between the stones just as between the bricks in a brick kiln. It is preferred that this layer of stone should not exceed six to ten inches in thickness.

"In some cases, temporary wooden flues, filled with straw, are erected, either one at the center or, if the heap is elliptical, one near each end, and the stone and coal are built up around them; thus, when they are burned out, a chimney or two is secured, which may be damped by pieces of stone or sod. Upon this first layer of stone is spread a layer of coal, and upon that a thicker layer of stone (12 inches), and so on, coal and stone alternating until the heap is topped with smaller stone.

The largest stones should be placed near the top of the heap, but not near the outside, so that they may be exposed to the highest heat. The proportion of coal is diminished in the upper layers, the effort being to distribute one-half of the total coal employed in the two lower layers, so as to secure the highest economy possible in the use of the fuel.

"Fire is then kindled in the straw or shavings; when the flames have communicated themselves to the cord wood and lowermost layer of coal, and tongues of flame shoot out from the crevices in the sides of the heap, earth, previously loosened by a few turns of the plow about the heap, is rapidly spread over the entire heap, thus damping the drafts and r.e.t.a.r.ding the combustion. Steam and smoke slowly escape during the first hours, but later the entire heap, including the outer covering of earth, is heated to a dull red glow. The burning goes on slowly for several days, the interior often being hot for several weeks. When the lower portion of the heap has reached an advanced stage of calcination, a portion of the outer layer of lime sometimes slips down; if so, a fresh covering of earth must promptly be applied at the exposed point; otherwise it will serve as a vent for the heat, and the top and other sides will fail of proper calcination."

[Ill.u.s.tration: Effect of Excessive Use of Burned Lime Without Manure at the Pennsylvania Experiment Station]

[Ill.u.s.tration: A Hydrated Lime Plant

(Courtesy of the Palmer Lime and Cement Company, York, Pa.)]

CHAPTER XII