Lime is applied to the soil mainly to make heavy soils lighter, to make sour soils sweet, to make certain mineral compounds soluble so plants can utilize them, and to act upon the organic matter and make it release plant food.
As to what form lime shall be applied in, J. C. M. Johnson of Lawrence county, Pennsylvania, writes: “I am confronted with the problem of applying lime to my soil, either in the form of ground limestone or of burnt lime. I have worked out the solution for the conditions on my own farm, where I can buy burnt lime at an adjoining farm at $2.50 a ton. I must import powdered limestone from Ohio, paying the heavy railroad freight of $1.60 a ton. If I lived near the works in Ohio and could haul the powder to my farm, the case might be different; or, if I lived near the south Illinois penitentiary at Maynard, I could buy powder at 6o cents a ton.
“The whole question is a chemical one. Its solution depends upon the quantity of the active lime that I would get in a ton. Limestone, or calcium carbonate, is composed in the proportion of 40 pounds of calcium with 12 of carbon and 48 of oxygen. By burning the stone, 44 pounds of carbon dioxide are driven off. That is, all the carbon and part of the oxygen are forced out by heat. The 56 pounds of quick or burnt lime left is called calcium oxide. By adding 18 pounds of water to the 56 pounds of burnt lime we get 74 pounds of slaked lime, or calcium hydroxide. Thus, 10o pounds of limestone, or 56 of burnt lime, or 74 of slaked lime, contain the same amount of calcium, which is the valuable part in either of the forms of lime mentioned.
” Which shall we use on our land-the ground limestone, the burnt lime, or the slaked lime? As each form contains the same valuable element, calcium, the question is evidently one of cost. In order to answer this, we must ask how much ground limestone is equal to 100 pounds of burnt lime. If burnt lime is worth $2.50 a ton, and limestone powder is worth $1.25 a ton at the works, and the freight on the powder $1.60 a ton, how much do I pay for enough limestone to equal one ton of burnt lime? It is easily seen that a ton of limestone powder costs $2.85.
“Now, how much limestone powder do I have to buy to get the equivalent of one ton of burnt lime? Of course, we must pay 20 times 179 pounds, or 3,580 pounds. This costs $5. Thus, if I apply limestone powder, I pay exactly twice as much for my calcium as when I use burnt lime at $2.50 a ton.
” From this discussion it is evident that the whole question narrows itself down to the comparative cost of each one of the two forms of lime considered. If a farmer can buy limestone powder for one-half what burnt lime costs, and the hauling distances are about equal, it matters little which he applies. Nevertheless, ease of application should be considered, for it costs much more in time, work, and hauling labor to apply 3,580 pounds than it costs to apply 2,000 pounds.
” Whoever is interested in lime, soil fertility, or soil renovation should read what leading authorities say on the subject in various books on soils.
There are, of course, other questions to consider besides the cost and ease of application in connection with the application of lime; for example, some authorities claim that burnt lime depletes the humus in the soil, and ground lime increases the humus content. Such questions are taken up in books on soils. The question I have been considering is one of the cost.”