Right Use of Lime in Soil Improvement

by Alva Agee

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 pure lime. 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, as limestones 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 on the 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 in excellent 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 magnesium from 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.