Chapter 26

APPLYING LIME

Forms of Lime.--There is unnecessary confusion in the mind of the public regarding the forms of lime that should be used. If amounts greatly in excess of needs were being applied, the form would be a matter of concern. There would arise the question of soil injury that might result from the use of the lime in caustic form. Again, if pulverized limestone were used, a very heavy application would bring up the question of coarseness in order that waste by leaching might be escaped. Most farms needing lime do not have cheap supplies, and the consideration is to secure soil alkalinity at a cost that will not be excessive. Freight rates and the cost of hauling to the fields, added to first cost of the lime, limit applications on most farms to the necessities of a single crop-rotation which includes clover, or, at the most, to two crop-rotations. Under these circumstances it is best to let cost of correction of soil acidity determine the form of lime to be used.

The material that will render the soil friendly to clover for the least money is the right one to select. We need to be concerned only with the relative efficiencies of the various forms of lime, as measured in terms of money. That which will most cheaply restore heavy clover growths to the land is the form of lime to be desired. The contentions of salesmen may well be disregarded as they produce confusion and delay a work that is important to the farmer.

Definitions.--The use of the various forms of lime will become general, and the terms employed to designate them should be understood. They vary in their content of acid-correcting material, and their correct names should be used with accuracy.

_Stone-lime_, often called lump-lime or unslaked lime, or calcium oxide or CaO, is a form widely known, and may be taken as a standard. It is the ordinary lime of commerce, and is obtained by the burning of limestone. One hundred pounds of pure limestone will produce 56 pounds of stone-lime (CaO).

_Pulverized lime_, often called ground lime, is stone-lime after being pulverized to permit even distribution. When it is fully exposed to the air or moisture, it slakes and doubles in volume.

_Hydrated lime_, often called slaked lime, is a combination of stone-lime and water. The water causes an increase in weight of 32 per cent, 56 pounds of stone-lime becoming 74 pounds of the hydrate.

_Pulverized limestone_, often called carbonate of lime, is the unburned limestone made fine so that good distribution may be possible.

_Air-slaked lime_, often called carbonate of lime, is stone-lime or hydrated lime combined with carbonic acid from the air, and thereby increased in weight. Fifty-six pounds of stone-lime, or 74 pounds of hydrated lime, become 100 pounds of air-slaked lime.

_Agricultural lime_, or land-lime, may embrace anything that the manufacturer of lime chooses to market. It may be reasonably pure unslaked lime, or it may have less value than a finely pulverized pure limestone. There is a custom of grinding the core, or partially burned limestone of the kiln, together with impurities removed from builders' lime, and with this may be put some air-slaked lime. Some manufacturers market under this name a lime of excellent value. There is no standard, and one should not pay more than a finely pulverized pure limestone would cost unless he knows that the content of fresh burned lime is high.

The element with which we are concerned in any of these forms of lime is calcium. It is the base whose union with the acids destroys the latter. It should be obvious that the addition of water to stone-lime, which adds weight and causes 56 pounds of the stone-lime to become 74 pounds of hydrated lime, adds no calcium. Likewise the change to the air-slaked condition adds no calcium, but again adds weight.

The Kind to Apply.--If a soil contains free acid, the amount of calcium needed is definite. The form of lime that can supply the need in that particular field at least expenditure of money and trouble is the one to be selected. A ton of stone-lime, or pulverized lime, can correct as much acid as 2640 pounds of hydrated lime or 3570 pounds of pulverized limestone, if all the original material was pure.

In other words, if the value of a given weight of pulverized limestone is placed at 100, the value of the same weight of hydrated lime would be 132 and the value of stone-lime would be 180, when each was finely divided and distributed throughout the surface soil.

The Fineness of Limestone.--Experiments at the Pennsylvania experiment station have shown that limestone has practically immediate availability in an acid soil if all of it has ability to pass through a screen having 60 meshes to the linear inch. Much of the limestone meeting this test doubtless is fine enough to pass through an 100-mesh screen. The requirement that a 60-mesh screen be used in testing is a satisfactory one to the buyer that wants immediate results in the field. A coarser product must be used in larger amount per acre, as only the fine particles are available at once, and the object of the application is to correct all the acidity. Where a coarse product, containing some fine particles, can be used at such a low price per ton that the application may consist of a large number of tons per acre, the practice may be commended, but the essential thing is immediate results, and only finely divided limestone can give them. Any long railway or wagon haul makes a heavy application of coarsely pulverized limestone inexpedient.

Hydrated Lime.--Many salesmen are too enthusiastic in their claims for hydrated lime. It has advantages over pulverized limestone, stone-lime, and pulverized lime, and there are disadvantages. The buyer of pulverized limestone pays for the haul on 100 pounds of material to get the 56 pounds of lime carried, while 74 pounds of the hydrate furnish the same amount of actual lime, if all of it is a hydrate. While the hydrate contains less strength than the stone-lime, it is in good physical condition for distribution, and the stone-lime must be slaked. The buyer will bear in mind, moreover, that much of the stone-lime which is burned on farms comes from limestone that is not very pure, and all impurity is waste. Most manufacturers of the hydrate locate their costly plants where the limestone is relatively pure. Prudent business reasons dictate such a course. A careful manufacturer of hydrated lime takes out imperfectly burned and other faulty material with screens. These advantages have some weight, but the fact remains that a ton of pure stone-lime has considerably more acid-correcting power than a ton of the hydrate.

Stone-lime.--Stone or lump-lime is composed of the 56 per cent of a pure limestone that gives value to the limestone. Forty-four pounds of waste material were driven off in the burning. Where railway or wagon hauls are costly, the purchase of stone-lime is indicated. There is advantage in getting this lime in pulverized form, provided it can be distributed in the soil before moisture from the air induces slaking and consequent bursting of the packages. The necessity of rapid handling has limited the popularity of pulverized unslaked lime, but no other form is equal to it when it is wholly unslaked. Some manufacturers grind the partially burned limestone often found in kilns, and furnish goods little better than pulverized limestone.

The slaking of stone-lime should be done in a large pile, and the distribution may be made with lime-spreaders. When the application is fairly heavy, a manure-spreader does satisfactory work. A good lime-spreader is to be desired, but care must be used to remove any stones or similar impurities in the slaked lime when filling it. Such spreaders are on the market.

The practice of slaking lime in small piles in the field is wasteful. It is difficult to reduce all the lime to a fine powder and to make even distribution over the surface. Any excess of water from rains puddles some of the lime, destroying practically all its immediate effectiveness. Distribution with shovels is necessarily imperfect.

The labor of slaking stone-lime and the difficulty in distribution are two factors to be considered when selecting the form of lime to be used. They may counter-balance in some instances the higher percentage of actual lime when comparison is made with the hydrate. That is a question to be decided by the buyer. He must be willing to use methods that will secure even distribution. The prevailing practice, however, of marketing the hydrate at a much higher price per ton than the stone-lime should prevent sales to farmers. The price paid for ease of handling is too great when purchase of the hydrate is made under such circumstances. It is better to do the slaking at home, furnishing the added weight of 32 per cent in water on the farm.

Ashes.--Hard-wood ashes have ceased to have much importance as a source of lime for land, but their use is held in high esteem even by those who regard fertilizers as mere stimulants and doubt the efficiency of lime. Hard-wood ashes, unleached, clean and dry, are valuable for acid soils. Their content of potash, which is variable and averages about 4 per cent, formerly was given all the credit for the soil improvement and increased clover growth that resulted from their use. Tests with other carriers of potash have shown that the potash probably produced only a small part of the effect noted, and the benefit is attributable to the lime in the ashes which exists in an effective form. The content of lime is variable, and largely so on account of the percentage of moisture and dirt that may be found in most ashes, and when no analysis has been made, the estimate of value should not be based on more than 30 to 40 per cent of carbonate of lime. The price of ashes runs so high, as a result of prejudice in favor of this well-known kind of soil amendment, that it rarely is advisable to buy them. Pure lime is a cheaper means of correcting the soil acidity, and the sulphate or the muriate of potash is by far the cheaper source of potash.

Marl.--Marls vary widely in composition. When quite pure, they contain 90 or more per cent of carbonate of lime, and have a value per ton about equal to finely pulverized limestone, and near half the value per ton of stone-lime. There are marls that are carriers of potash and phosphoric acid, and are to be valued accordingly as fertilizers.

Magnesian Lime.--Some limestone is a nearly pure calcium compound, and yields a pure lime, while much limestone contains a high percentage of magnesia. The latter is preferred by manufacturers who furnish pulverized lime because it does not slake readily, and is less liable to burst the packages before required for use. A pound of magnesian lime will correct a little more acid than a pound of pure lime, and no preference may be shown the latter on that score. There are soils in which the proportion of magnesia to pure lime is too great for best results with some plants, as plant biologists assure us, but there is too little definite information respecting these soils to justify one in paying more for a high calcium lime than for a magnesian lime when it is to be used on acid land. The day may come when more will be known, but the rational selection to-day is the material that will do the required work in the soil for the least money.

Amount per Acre.--The amount of lime that should be applied to an acre of land depends upon the degree of its acidity, the nature of the soil, the cheapness of the lime, and the character of the crops to be grown. The actual requirement for the moment could be determined by a chemical test, but the application should carry to the soil an amount in excess of immediate requirement. When clover has ceased to grow within recent years, it is a fair inference that the deficiency, if it exists, has not become great. When sorrel and plantain have gained a strong foothold, indicating that good grasses are unable to replace clover, the degree of acidity probably is higher. The results of tests at experiment stations and on farms show that 1000 pounds of pulverized lime, or one ton of pulverized limestone, evenly distributed throughout the surface soil, can restore clover to the crop-rotation on much land. This is an application so light that a state of alkalinity cannot be long retained. It is better to apply the equivalent of a ton of stone-lime in the case of all heavy soils that have shown any acidity. Where lime is low in price, 3000 pounds of stone-lime, or its equivalent in any other form of lime, is advised, the belief being that such an application will maintain good soil conditions through two crop-rotations, or eight to ten years. This amount can be applied quite successfully with a manure-spreader, and meets the convenience of the man who burns his own lime and does not want to screen it for use in a lime-spreader. The man who must buy his lime, and pay a freight charge upon it, will find it better to use only a ton per acre. This advice applies to heavy soils. A light, sandy soil should be given only a small application, as otherwise physical condition may be injured. The lime, used in excess, has an undue binding effect upon the sand. An application of 1000 pounds of stone-lime per acre can be made with safety.

Time of Application.--The use of lime on land should be associated in the land-owner's thoughts with the growing of clover. It does help soil conditions so that more grain can be produced, but if it is permitted to displace the use of fertilizers, and does not lead to the growth of organic matter, harm will result in the end. Lime should be applied to secure clover, and therefore it should be mixed with the soil before the clover is sown. The application may be made when fitting the seed-bed for the grain with which clover usually is seeded, or may be given a year or two years previous to that time. The important point is to have the soil friendly to plant life when a sod is to be made.

Lime should be put on ground always after the plowing, and it should be well mixed with the surface soil. Even distribution is just as important in its case as in that of fertilizers. A good practice is to break a sod for corn, harrowing and rolling once, and then to put on the lime. A cut-away or disk harrow should be used to mix the lime with the soil before any moisture causes it to cake. When large crumbs form, immediate efficiency is lost.

If the application is light, and may barely be equal to immediate demand, it is better practice to put on the lime when preparing the seed-bed for the wheat or other small grain in which the clover will be sown. It should never be mixed with the fertilizer nor applied with the seed. The lime should go into the soil a few days, or more, prior to the seeding. The soil having been put into a condition favorable to plant life, the seeding and the use of commercial fertilizers should proceed as usual.

Lime should never be mixed with manure in the open air, but it is good practice to plow manure down, and then to use lime as indicated above, if needed. If manure and lime must be used after the land has been plowed, the lime should be disked well into the soil before the manure is applied, and it is advisable that the interval between the two applications be made as long as possible.