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 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 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 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 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 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 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.