Technicians generally recommend that limestone be applied at least 6 months to a year before seeding legumes, especially when a field is limed for the first time because young alfalfa and clover need abundant calcium.

Lime may be applied at any time of the year on land plowed for cultivated crops in the spring where small grains and legumes are to follow; on land plowed for winter grain with a legume to follow; on land following harvest of cultivated crops; on sod ground before plowing for a cultivated crop; and on permanent pasture.

Lime is spread by trucks, two-wheeled lime or fertilizer distributors, and end-gate lime spreaders. Most of the lime is spread by custom operators. Trucks equipped with V-shaped beds and centrifugal spreaders at the rear are used for hauling and spreading. Lime can be applied in that way on plowed ground, but many truckers prefer to spread lime on sod, pasture, or cultivated crops after the harvest. Applications in late summer or fall are usually most convenient, because then the roads and fields are generally in a good condition.

In places where hydrated or burned lime is applied or when lime is shipped in by railroad car and when weather conditions prevent the use of heavy trucks, a two-wheeled, box-type spreader is commonly used. Some equipment, designed for lime or fertilizer, can haul more than 1,000 pounds and apply lime at the rate of 2 tons an acre.

Grain drills equipped with fertilizer compartments can be used to apply small amounts of lime at seeding time or in a separate operation, but they cannot be used for materials high in moisture, such as marl.

The endgate spreader attached to the end of a wagon box has been used to spread lime. Special attachments of this type are available for manure spreaders. Many dairy farmers mix limestone with manure before loading or dump lime on the top or bottom of a load of manure. Up to 200 pounds of limestone to a ton of manure may be spread without a special operation.

MORE THAN 400 million tons of limestone were used in 35 States in the period 1930-1954. The ten North Central States used about 3.5 times as much lime as any other region. Second highest in the use of lime were the East Central States. Next were the Northeastern States and the Gulf States.

The Northeast, East Central, and North Central States increased their limestone consumption 5, 6.5, and 12 times, respectively, from 1930-1935 to 1950-1954, but a 58-fold increase occurred then in the Gulf States.

The total tonnage used in Illinois in 25 years was almost double the amount used in any other State. Indiana, Ohio, Iowa, Wisconsin, and Missouri each used 30 million to 40 million tons in 1930-1945. Pennsylvania and Kentucky each used about 21 million tons of limestone.

Assistance payments for liming as a soil conserving practice, together with an improvement in farm income and an intensive educational program, boosted limestone consumption from less than 4 million tons in 1935 to more than 30 million tons in 1947. Between 1940 and 1949, 80 to 95 percent of the limestone used in most States was bought under an assistance program. In 1954 less than 67 percent of lime was purchased through the Agricultural Conservation Program.

The amount used has dropped since 1947; less than 20 million tons of agricultural limestone were used in 1954.

Our agricultural soils still need large amounts of lime. Agronomists of land-grant colleges and universities in 37 States estimated in 1956 that 161 million acres would be improved by Timing. They estimated that the lime required for those soils in 1956 on a corrective basis (rather than an annual basis) would be more than 332 million tons, or an average application per acre of slightly more than 2 tons. If the total figure is compared with the 407 million tons of limestone used in 1930-1954, the actual lime requirement for maximum crop production is about 8o percent of the amount used then.

Data compiled by the National Agricultural Limestone Institute indicated that the limestone tonnage for the Nation in 1954 was only 23.5 percent of the annual needs. On that basis, about 8o million tons of lime would be required annually.

Legal regulations control the quality of limestone that is sold. A number of States include restrictions on liming materials in their fertilizer laws. Others group lime with fertilizer, regulating both as agricultural minerals.

About half the States have laws that apply to specific agricultural liming materials and generally list the materials that qualify as lime. Almost all States require the licensing of manufacturers, dealers, and importers, and the labeling of their products.

Bagged or packaged materials generally must carry the name, brand or trademark, the name and address of the manufacturer, the minimum neutralizing value in terms of calcium carbonate or calcium oxide, and the percentages of the total material that will pass certain screens.

The purchaser of lot or bulk material usually receives an invoice or waybill bearing such guarantees.

Few States have set up legal limitations as to the purity and fineness of liming materials. Delaware, Maryland, Rhode Island, and Wisconsin have laws establishing required degrees of purity. Alabama, North Carolina, Ohio, Rhode Island, Virginia, and Wisconsin have set up legal standards of fineness for one or more grades of liming material.

The specifications for lime set by the Agricultural Conservation Program have brought considerable uniformity to standards of fineness and neutralizing value. In order to qualify in this program, lime must pass the specifications set up by State committees of the Agricultural Conservation Program. For instance, 15 States have set a minimum neutralizing value of 80 percent for standard ground limestone, 8 States have legalized a minimum level of 85 percent, and 12 States require a neutralizing value of at least 89.2 percent calcium carbonate equivalent.

In States where marl and refuse-lime from sugar beet factories, paper mills, and water-softening establishments are sold, a minimum of 70 percent on a dry basis is commonly accepted. Since these materials are often sold on a volume basis, the ACP specifications of several States require that a cubic yard contain 800 pounds of calcium carbonate. Carbide refuse-lime must have a neutralizing value of 85 percent.

The minimum neutralizing value for blast furnace slag is quite variable in six or seven States where it is distributed. One State accepts slag as low as 70 percent calcium carbonate equivalent.