Crops and Methods for Soil Improvement. Alva Agee

      Red clover on limed and unlimed land.

      A Practical Test.—The importance of alkalinity in soils is so great, and the prevalence of acidity has such wide-spread influence to-day, limiting the value of the clovers on a majority of our farms, that a simple and more convincing test is suggested here. Every owner of land that is not satisfactorily productive may learn the state of his soil respecting lime requirement at small expense. When a field is being prepared for seeding to the grain crop with which clover will be sown, a plat containing four square rods should be measured off, and preferably this should be away from the border to insure even soil conditions. A bushel of lump-lime, weighing eighty pounds, should be slaked and evenly distributed over the surface of the plat of ground. It can be broadcasted by hand if a spreader is not available, and mixed with the surface soil while in a powdered state. The plat of ground should be left as firm as the remainder of the field, so that all conditions may be even for the test. The appearance of the clover the following year will determine whether lime was needed or not. There is no reason why any one should remain in doubt regarding the lime requirement of his fields. If income is limited by such a cause, the fact should be known as soon as possible.

      Duration of Effect.—Soil acidity is not permanently corrected by a lime application. The original supply failed to prove lasting, and the relatively small amount given the land in an application will become exhausted. The duration depends upon the degree of acidity, the nature of the soil and its crops, and the size of the application. Experiments at the Pennsylvania experiment station have shown that an application only in sufficient amount to correct the existing acidity at the time of application will not maintain an alkaline condition in the soil, even for a few months. There must be some excess at hand to unite with acids as formed later in the crop-rotation, or limings must be given at short intervals of time to maintain alkaline conditions.

      Experience causes us to assume that enough lime should be applied at one time to meet all requirements for a single crop-rotation of four, five, or six years, and, wherever lime is cheap, the unpleasant character of the labor inclines one to make the application in sufficient amount to last through two such rotations. It is a reasonable assumption, however, that more waste results from the heavier applications at long intervals than from light applications at short intervals. In any event need will return, and soil acidity will again limit income if applications do not continue to be made.

CHAPTER III

       Table of Contents

      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