An Indiana Limestone QuarryAn Indiana Limestone Quarry
A Limestone Plant (Courtesy of the Michigan Limestone Company)A Limestone Plant (Courtesy of the Michigan Limestone Company)
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 ahard 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 nowexists 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.
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 intheir 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.
A Limestone Pulverizer for Farm Use (Courtesy of the Jeffrey Manufacturing Company, Columbus, Ohio)A Limestone Pulverizer for Farm Use (Courtesy of the Jeffrey Manufacturing Company, Columbus, Ohio)
A Lime Pulver in Operation (Courtesy of the Jeffrey Manufacturing Company)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 theinvestment 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 grindingplants 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 ½ 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.
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 substitute for manure, sods and commercial fertilizers. Immoderate use gave increased crop yields for a time, and the inference waseasy 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 oystershell, 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 CaCO3. When heat is applied under right conditions the carbon dioxide, CO2, 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 freshburned 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 quantity 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 judicialtemper 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 quantity 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.
Laying Foundation for a Lime Stack at the Pennsylvania Experiment StationLaying Foundation for a Lime Stack at the Pennsylvania Experiment Station
A Stack Nearly Completed at the Pennsylvania Experiment StationA Stack Nearly Completed at the Pennsylvania Experiment Station
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 hasbeen, 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 passages into the interior of the heap. Between the chinks 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 chinks 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 arebuilt 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 retarding 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."
Effect of Excessive Use of Burned Lime Without Manure at the Pennsylvania Experiment StationEffect of Excessive Use of Burned Lime Without Manure at the Pennsylvania Experiment Station
A Hydrated Lime Plant (Courtesy of the Palmer Lime and Cement Company, York, Pa.)A Hydrated Lime Plant (Courtesy of the Palmer Lime and Cement Company, York, Pa.)
Slaking Lime.The usual means of reducing fresh burned stone lime to a condition that makes even distribution upon land possible is by slaking. A few years ago considerable effort was made to create a market for lime pulverized by machinery, but the difficulty in excluding the moisture of the air so that packages would not burst has been in the way of developing a market. Slaking, by the addition of water to the fresh burned lime, is the common method of getting the required physical condition. When the slaking is done on the farm, the custom has been to distribute the lime in small piles in the field, placing the piles at such convenient distance apart that the lime, after slaking, could be spread easily with a shovel.
The water for slaking comes from rains, or from moisture in the air and earth. The method is wasteful and can be justified, if ever, only where farm-burned lime costs little per ton, and the nature of the soil issuch that a relatively heavy application can be safely made. The distribution is necessarily uneven, and if the required amount goes upon all the surface, a great excess is sure to go upon a portion of it. Very often an excess of water puddles much of the lime in the pile, and lumps may be seen lying in ineffective form in the soil for years. The practice is responsible for much of the excessive application that brought the use of caustic lime into disrepute.
Slaking in Large Heaps.A preferable method is to put the lime in flat heaps of large size and about four feet deep, so that water may be applied or advantage be taken of rainfall. The value of the lime is so great that one can well afford to draw water and apply with a hose so that the quantity can be controlled with exactness. When fresh burned lime is perfectly slaked, each 56 pounds of pure lime becomes 74 pounds of hydrated lime, water furnishing the added weight.
Hydrated Lime on the Market.A popular form of lime on the market is the hydrate. Manufacturers first burn the stone, and in the case of a pure limestone they drive off 44 pounds of each 100 poundsof the weight in burning. Then, they combine enough water with the lime to change it to hydrate form, and that adds 18 pounds weight. It is run through a sieve to remove any coarse material, and then packed in bags which help to exclude the air. The small packages in which it comes upon the market make handling easy, and this helps to bring it into demand. Its good physical condition makes even distribution possible, and thus permits maximum effectiveness to be obtained. It is only slaked lime, identical in composition and value with lime of the same purity slaked on the farm, but some dealers have been able to create the impression that it has some added quality and peculiar power. This does no credit to the public intelligence, but the hunger of soils for lime is so great that investment at a price wholly out of proportion to the price of farm-slaked lime has rarely failed to yield some profit.
Degree of Purity.It is always a reasonable assumption that hydrated lime has been made from stone of a good degree of purity. A local stone, burned on the farm, may be of low grade, but no man of business judgment would erect a costly plant forburning and hydrating lime where the purity of the stone would not afford a good advertisement in itself.
On the other hand, we find very little hydrated lime on the market that has not had sufficient exposure to the air to become changed in some part to an air-slaked condition, or has had refuse mixed with it. Air-slaked lime is not worth as much per ton as the hydrate because it cannot correct as much soil acidity, and the percentage of the former cannot be determined by the buyer. Its presence may not be due to any wrong-doing of the manufacturer, and, on the other hand, the increase in weight that attends air-slaking may be welcomed in some degree by a dishonest manufacturer before the goods are shipped. The difficulty in preventing hydrated lime from adding to its weight by becoming air-slaked is a point to be taken into consideration.
The percentages of air-slaked material in hydrated limes are widely variable, and no manufacturer can standardize his product on the market surely for the benefit of the farmer. In some instances the product is adulterated with refuse material in finely pulverized condition.
Air-Slaked Lime.A pure limestone is a carbonate, and the chemical formula is CaCO3. When it is burned, the carbon dioxide (CO2) is driven off, leaving CaO, which is calcium oxide, called fresh burned lime. In this process 44 pounds of a stone weighing 100 pounds passes into the air, and there remain 56 pounds of lime. When it air-slakes, it takes back the carbon dioxide from the air, and the new product becomes CaCO3, or carbonate of lime, and regains its original weight of 100 pounds. This is what would happen if the process were complete, and it is nearly so when the exposure to the air is as perfect as possible.
Fifty-six pounds of valuable material are in the 100 pounds of air-slaked lime, just as is the case with limestone, and there is no difference in effectiveness except in so far as the air-slaked material is absolutely fine and available, while most pulverized limestone is less so. In making purchase for use of land the buyer cannot afford to make anyappreciable difference in price in favor of air-slaked lime, as compared with a fine stone.
Air-Slaking a Slow Process.Lime changes to an air-slaked condition slowly unless it has full exposure. Old heaps will remain in hydrate form for many years, excepting the outside coat, which excludes the air. Complete air-slaking would not reduce ability to correct soil acidity, the total amount of calcium and magnesium remaining constant, but weight would be added in the slaking, and therefore the value per ton would be reduced. The slowness with which air-slaking proceeds gives reason to expect that any bulk of old lime may contain a considerable percentage of the hydrate, and therefore have greater strength than a true carbonate like limestone. This is a consideration of value to a buyer.
Agricultural Lime.Some manufacturers have found in the demand for lime by farmers an opportunity of disposing of much material that would not be satisfactory to manufacturers and builders. In some cases this so-called agricultural lime is sold at a price that is not beyond value, but it varies much in its content of purelime. If the unburned cores of kilns are ground up, the material simply retains the value of unburned stone. Any air-slaked material put into it has like value. Forkings, ground up, have less value, and sometimes no value at all. Some better material may go into this mixture that is given the name "agricultural lime," and the product cannot be standardized or have a valuation given it that would be true for another lot.
Some manufacturers are marketing limes of fair values under this designation, but the values change as the material changes. There are other manufacturers who are putting poor stuff on the market. Unless one knows the manufacturer and his processes, he should not pay a great deal for "agricultural lime." It is much better to buy a high-grade lime or limestone that is more nearly constant in composition. When the word "agricultural" is part of the brand, there is assurance that the percentage of waste stuff in it is relatively high. Unless one knows to the contrary, he should assume that a ton of finely pulverized limestone is worth more per ton than "agricultural lime."
Marl.Marls vary in composition, aslimestones do, but there are beds of chalky marl that contain very little clay and sand and are nearly a pure carbonate. It is only marls of high degree of purity that can be put on the market with profit, but beds of less pure marl furnish dressings for farms of the locality in many sections of the country. Some of these inferior marls have had so much clay and sand mixed with the lime carbonate that dressings must be heavy. The best lime marls provide excellent material for the correction of soil acidity, the actual value per ton being practically the same as that of the finest pulverized limestone. Some dealers in marl make extravagant claims for their goods, but any farmer may easily put these claims to the test and learn that he should not expect more than a fairly good carbonate of lime can do.
Marl improves the physical condition of stiff soils only when used in large amount per acre, and this is true of any carbonate form, such as limestone. Little effect upon physical condition should be expected from the light application usually given when marl is purchased and transported some distance to the farm. The chalk marl onthe market is used to correct soil acidity, and at the best it is worth only what good lime carbonate is worth. It has no hidden virtues, and cannot take the place of fertilizers. It is an excellent means of meeting the lime-requirement of land when bought right, and its fine division makes it distinctly superior to coarse stone.
There should be no confusion of a lime marl with the so-called "green sand" marl. The latter is low in lime, and may be acid, the value of the marl being in a considerable percentage of plant food contained.
Oyster Shell.Ground oyster shell is a good source of carbonate of lime. The percentage falls below that of limestone, but in addition there is a little nitrogen and phosphoric acid. An analysis of a good quality of oyster shell, as found on the market, will show 90% carbonate of lime.
Burned oyster shell has something near the same composition as lime made from stone, but it goes back to hydrate and air-slaked forms rapidly. There is no large amount of burned shell lime on the market, the material known as shell lime being the ground shell, or lime carbonate.
Wood Ashes.A large supply of lime inexcellent form was afforded by hardwood ashes, but this product has ceased to have any important value to our agriculture. The chief supply on the market is low in quality, containing moisture and dirt in considerable amount, the form of lime being changed from an oxide to the hydrate and carbonate.
Gas Lime.Prof. E. B. Voorhees, in "First Principles of Agriculture," says: "Gas lime is also frequently used as manure; in gas works, quicklime is used for removing the impurities from the gas. Gas lime, therefore, varies considerably in composition, and consists really of a mixture of slaked lime, or calcium hydrate, and carbonate of lime, together with sulfites and sulfides of lime. These last are injurious to young plant life, and gas lime should be applied long before the crop is planted, or at least exposed to the air some time before its application. The action of air converts the poisonous substances in it into non-injurious products. Gas lime contains on an average 40% of calcium oxide, and usually a small percentage of nitrogen."
Lime After Magnesium Removal.A by-product in the removal of magnesiumfrom a magnesian limestone is an excellent material for correction of soil acidity, on account of its physical condition. Its exposure to the air causes much of the hydrate to change to an air-slaked form, and its value per ton lies somewhere between that of very finely pulverized limestone and hydrated lime.
Magnesium.As an element of plant food, magnesium is as essential as calcium. It leaches out of the soil less readily, and there may be even less need of its application as a plant food, though the need of calcium applications for this purpose is assumed to be small. In the correction of soil acidity magnesium is more effective than calcium, 84 pounds of the carbonate being equal to 100 pounds of calcium carbonate. It is a curious fact, however, that there is widespread fear of magnesium as a soil amendment. This is not traceable to any considerable experience by practical farmers that inspires caution in its use, although immense quantities of magnesian limestone and lime have been used. Neither is it due to any weight of evidence against it in the experience or teachings of soil chemists and experiments. The facts of the case appear to be as follows:
1. An investigator found in his laboratory that a plant growing in a water solutionwas injured when magnesium was added, and that the injury was checked when calcium in equal amount was added to the water. The theory was worked out that a soil should not contain a greater total amount of magnesium than of calcium, and as the soil's supply of calcium tends to leach out more readily than the supply of magnesium, it was best to use a high-calcium lime. If this discovery of the laboratory had been carried into the field, its significance would have dwindled to zero in the case of normal soils, and a lot of exploitation would have been rendered impossible. As it was, the discussion went merrily along until it occurred to some one to test the matter in the soils where plants grow, and one would now hear little of it if commercial interests were not at stake.
2. Very much of our limestone supply is high in magnesium, and some men who have limestone very low in magnesium and high in calcium have done a good stroke of business for themselves by deepening the public's impression, due to laboratory tests with water cultures, that magnesium in lime is injurious.
3. Many people knew "lime," but had noknowledge of magnesia, and if it was an impurity like clay or sand, cutting down value per ton, and if it was worse because harmful, they wanted none of it.
The Fact's Importance.If every farm could get its supply of pure calcium lime as cheaply as it can have magnesian lime, the truth respecting the value of the latter would have small agricultural importance, but as a great bulk of farm and commercial supplies of lime is magnesian, financial injury has been done consumers who have paid more than should have been paid for relatively pure calcium lime and limestone, being afraid to use goods whose content of magnesium was not small. It is poor policy to use either kind of burned lime in great excess, but when rationally used on all soils except sandy ones, there is no preference to be exercised that can be based upon performance. A magnesian lime corrects as much acidity as a high calcium lime, and a little more, and its use is to be recommended if there is any advantage in the matter of price, except in the case of distinctly sandy soils.
Magnesian Limestone.Leading scientists making tests of limestone for normalsoils, use magnesian limestone freely. They recommend its use to farmers wherever there is advantage in point of price. The advice is safe that the limestone of a given fineness should be chosen whose total percentage of carbonates of calcium and magnesium is the highest. The example of these scientists, buying pulverized limestone for agricultural colleges and experiment farms, and for their own farms, should loosen the curious hold that the early warnings of a laboratory experimenter took upon public imagination. The farmer should buy limestone on a basis of ability to correct soil acidity, and make each dollar do the most possible toward that end.
Most limestones contain some percentage of magnesium, and in the case of a pure dolomite over 45% carbonate is present in combination with calcium carbonate. A stone rich in magnesium slakes less readily than one high in calcium, and therefore is preferred by manufacturers shipping pulverized burnt lime to reach its destination before slaking.
Relative Values.The relative strengths of the various materials containing lime may be known and yet doubt continue respecting the choice to be made. The conflicting claims of dealers, and inaccurate deductions from a single test made by some individual, aid the confusion. If there were always the single purpose of correcting soil acidity, and if there were the same ease of application in case of all the materials, the choice would present much less difficulty. Notwithstanding this, most land now has a lime requirement, or will have one as leaching, crop removal and chemical change within the soil continue, and the puzzle is no worse than a score of others that present themselves continuously in farming.
Destroying Acids.The cost of liming to improve the physical condition of land is prohibitive for most farms remote from supplies of stone that can be burned and put upon the land at a low price per ton. Where stone is at hand, and soils are intractable, lime burned on the farm should be used. Some slight benefit to a stiff soil may be obtained from the light application that is deemed practicable where all forms are costly, but this benefit is not usually marked in case of an application of a ton or less of burned lime. It is a safe statement that most buyers of lime in some form or other will profit chiefly through the correction of soil acidity and promotion of bacterial life. This renders the situation more simple as any carbonate, hydrate or oxide of lime will accomplish these purposes.
Composition.The first consideration is the actual content of calcium and magnesium. A guaranteed analysis is the only safe basis of purchase. The unstable nature of fresh burned and hydrated forms makes an exact statement of percentages impossible for goods not wholly fresh, but at least the purity of the original limestone can be judged.
Equivalents.One ton of fresh burned lime, made from pure stone, is equivalent to 2640 pounds of the hydrate, and to 3570 pounds of pulverized limestone or of air-slaked lime. It is easy to carry in mind the proportions expressed by 1, 1⅓ and 1¾.If there were no other considerations, such as convenience in handling, evenness of distribution, etc., to take into account, one ton of fresh burned lime, one and a third tons hydrated and one and three-quarters tons finely pulverized limestone would have the same value when delivered in the field. Lime fully air-slaked, high-grade marl, and finely pulverized limestone would have the same value, ton for ton.
Even Distribution.The value of even distribution is not easily overestimated. If lime in proper amount does not go into each square foot of an acid soil, some of the soil will remain sour unless mixing is done by implements of tillage. Lime is diffused laterally through the soil in a very slight degree. If a strip of sour land is protected by canvas, so that no dust from lime applied to uncovered land can blow upon it, a seeding to clover will show that plants a few inches from the edge of the limed area will fail to start thriftily and may die before their roots reach the lime. Full effectiveness of an application is possible only through even distribution.
Using Lump Lime.Lump lime, slaked on the farm, is difficult to apply satisfactorily. Spreading with a shovel from small heaps is bad practice, and when the lime is slaked in a large heap, it cannot be handled as well as pulverized stone or commercial hydrated lime. The latter two are in condition for application by means of a lime distributor, or even a fertilizer attachment of a grain drill. The farm-slaked lime contains impurities that interfere with distribution.
An Estimate.It is always hazardous to attempt an estimate of cost of labor without knowing the particular farm conditions, but the expense and discomfort attending the slaking and use of lime bought in lump state justify a willingness to pay as much for a ton of hydrated lime as lump lime would cost, although the former has only three-fourths as much strength as the latter. Some farmers pay nearly twice as much for the hydrated, partly to escape the inconvenience and partly because they hope that the extraordinary claims for superiority made by some dealers may prove true. They should know that it is only fresh burned lime slaked, but incline to credit a claim that special treatment enhances value in some mysterious way.
Comparing lump lime with finely pulverized limestone, the factors of expense and discomfort and final lack of perfect distribution of the former remain important. The stone is relatively easy to handle, being slightly granular and passing through a distributor without trouble. The fact that it is not caustic, like the hydrated, is in its favor. When everything is taken into account, one is justified in using limestone or air-slaked lime at a cost per ton three-fourths as great as that of lump lime. It is to be borne in mind that in these estimates the cost per ton is not that at the factory or at one's own railway station, but on the farm. The freight and cartage to the farm are based on weight of material, and more material per acre is required when the worthless portion has not been driven off by burning. If one must use one and three-quarters tons of limestone to have the equivalent of one ton of fresh burned lime, it is evident that the cost of freight and cartage of the worthless portion might make cost prohibitive if distances were very great. Farms lying a long distance from a railway station may easily find that fresh burned lime is the only form of lime theycan afford. The basis for correct estimate is cost delivered in the field.
Storage.One advantage possessed by the limestone is ease of storage. There is no inconvenience or loss. The stone may be ordered at any time of the year when teams are least busy upon other work, and it can be held till wanted. In this way the cost of cartage to the farm may be kept relatively low, and the material is at hand when wanted, regardless of rush of work or delays of railroads. This advantage is partial counterbalance to the cost of freight on the worthless portion of unburned stone.
Valuing Limestone.The estimates, so far as labor and convenience are concerned, are merely suggestive, and rest upon the presumption that the stone is satisfactorily fine. It has been urged in another chapter that immediate effectiveness is determined by fineness, but as a working basis we assumed that when all the stone would pass through a screen having sixty wires to the inch it would give the desired results. The coarsest portion would not be available at once, but when an application is heavy enough to serve for a year or more, we have enough very fine material in such a grade ofstone to meet immediate need. When estimating values of such a grade and coarser grades, the amount per acre to be used is a factor. The coarse is unsatisfactory if the price is not low enough to permit an application sufficient for a considerable term of years, so that it will contain all the fine material needed at once. In that case the coarser material may be expected to meet later need, and may be even more desirable for such purpose, as it would not be subject to leaching.
Coarse grinding costs much less than fine grinding, and it is the resulting low price that permits the heavy application. As stone varies in hardness and ability of the small particles to withstand disintegrating forces in the soil, an estimate of the difference in price between a 60-mesh limestone and a 10-mesh one could not serve as a safe guide. The buyer should know the percentages of a limestone passing through screens of various sizes before he makes a purchase, and should demand part of the saving in cost of production that attends coarse grinding.
Oyster Shell.Ground oyster shell should be given about the same valuation aslimestone. It is a lime carbonate, and the percentage of worthless material in it varies somewhat It is coarsely ground, but the large pieces disintegrate in the soil much more rapidly than limestone would do. It contains a little nitrogen and phosphoric acid, partially available, as an offset to coarseness and some lack of purity, as compared with the highest grade of fine stone. It is profitable to buy oyster shell at limestone prices if used liberally enough to furnish a supply for a term of years. The oxide, or burned shell lime, would be nearly the equivalent of burned stone if it did not change to hydrate and air-slaked forms so rapidly that it rarely is on the market in thefullstrength of fresh burned lime.
Hardwood Ashes.As a source of lime, ashes have become far too expensive. The composition of ashes on the market is widely variable, dirt and moisture often accounting for much of the weight. The lime in fresh burned ashes is peculiarly effective, being finely divided and in oxide form, but the ashes on the market have much of the lime water-slaked and air-slaked. Unless analysis is made at time of purchase, a buyer should not estimate the content of lime in aton at a value greater than assigned to one-half of a ton of limestone. The additional value of the ashes, due to the potash content, is wholly another consideration.
Marl.No more should be paid for a ton of good chalk marl than an equal weight of fine limestone would cost. Each is a good carbonate of lime, with the same capacity for destruction of acids.
Agricultural Lime.This variable product should not be bought unless actual composition is known, or the cost is as low as that of pulverized limestone, and even then it may be a bad purchase, the methods of the manufacturer being the determining factor. If such lime is chiefly a dumping place for low-grade stone and forkings, it has small agricultural value.
Land Plaster.The soil wants lime in carbonate form. The oxide and hydrate change to carbonate, and therefore are good. Land plaster is a sulphate, and its tendency is to make a soil sour. It should not be considered as a means of correcting soil acidity.
Basic Slag.The amount of effective lime in basic slag, as made by modern methods, is so small that its value is nearly negligible. Basic slag is a good source of phosphorus, and in addition has a tendency toward correction of soil acidity, but such tendency has little cash value for land that requires a considerable dressing of lime to furnish a base with which soil acids may combine.
An expression of opinion was obtained recently from some leading soil chemists of this country, and upon such expression we base the estimate that when pulverized limestone costs three dollars a ton, the value of the lime in a ton of basic slag should not be placed higher than 50 cents, and some chemists believe that the lime content is entirely negligible as an agent in soil amendment.
Lime in Other Fertilizers.The demand for lime is leading some men to state a lime content for their goods that is designed to mislead. Such lime is not in a form to combine with soil acids, and is as valueless as the very large amount of lime in acid soils that is in compounds having no power to affect free acids.
A Controlling Principle.The chief purpose of liming land is to provide a base with which acid may combine, so that the soil may be friendly to plant life. Lime has little power to distribute itself through a soil, and harmful acid may remain only a few inches distant from the point where lime has been placed. In a general way, the tendency of lime is downward, especially when the application at the surface is heavy. Economical use demands even distribution through the soil so that a sufficient amount is in every part. Means to that end are good means of distribution.
Spreading on Grass.Where lime is burned on the farm, and little account of labor is taken, it has been a common custom to spread the lime on grass sods the year previous to breaking the sod for corn, using 100 to 300 bushels per acre. Rains carried some of the lime through the soil, and the increased yields for a few years were due to the improved physical condition of a stiffsoil that a heavy application of caustic lime produces, and to the disintegration of organic matter and to change in compounds of mineral plant food. The practice is rightly going into disrepute, being wasteful and harmful.