More Crops, Lower Costs

Agricultural Lime May be the Key

By Eric Marcotte,

AGRICULTURAL LIME, OR AGLIME, is a soil conditioner most commonly produced from finely crushed limestone. It provides a source of calcium and magnesium for plants, increases the pH of acidic soil, enhances water penetration, and improves the uptake of nitrogen, phosphorus and potassium r NPK. For farmers, this means lower crop production costs, but for quarries with the proper chemistry for Aglime production, it equals another product to sell.

Reducing soil acidity reduces unfavorable conditions caused by iron, aluminum and manganese. It also increases the availability of critical plant nutrients (nitrogen, phosphorus, and potassium) by providing an environment that allows micro-organisms to break down organic matter, and it increases the effectiveness of herbicides. The Michigan State University's Extension Bulletin E-1566 states, "Aglime can return $5 to $10 for each dollar invested in lime. Raising soil pH from 5.7 to 6.5 in mineral soils may improve corn or soybean yields by 20 percent or more, and alfalfa yield by 35 percent or more."

When Aglime comes in contact with the acids in the soil, calcium (Ca) moves to the surface of soil particles, replacing the acidity. The acidic H+ ions react with the carbon-ate (C03) to form carbon dioxide (CO2) and water (H20). The result is a soil that is less acidic (has a higher pH). Why does size matter for Aglime? The smaller the particle size, the higher the percentage is absorbed in the soil within the first year of application. Particles smaller than 50 mesh - 100 mesh are completely absorbed within the first year of application - 100-percent effective. Particles between the 10 mesh X 50 mesh sizes are 50-percent effective over a three-year period. Materials larger than 10 mesh are considered too large to dissolve within a three- to four- year time period. The decision of what mesh size to use depends on how rapidly the farmer wants the full value of Aglime to be realized.

Aglime Materials, Chemical Composition, and Calcium Carbonate Equivalent (CCE)

The second major factor that deter­mines Aglime quality is chemical composition. Chemical composition determines an Aglime material's amount of acid it can neutralize. Pure calcium carbonate (CaC03) has an acid neutralizing value of 100 percent. When an Aglime material is evalu­ated, it is compared to calcium car­bonate, and its neutralizing value is called the Calcium Carbonate Equivalent (CCE) value or percent CCE.

To sell Aglime to different regions, review the state requirements for percentages passing the different mesh sizes and the calculation required to provide the required Calcium Carbonate Equivalent.

Most U.S. states have unique specifications for Aglime.

The following states don't list sieve sizes: Arizona, Hawaii, New Mexico, North Dakota, Rhode Island, South Dakota, Texas, Utah and Wyoming. Colorado and Nevada have alkaline soil that requires the addition of acids to adjust soil pH.

Types of crushing methods used for Aglime production.

The primary crushing method used is impact with Cage Mills, Hammer Mills, and Vertical Shaft Impactors (VSI).

Cage Mills

Final prod­uct size is controlled by pin spacing and cage speeds. Cage mills have lower maintenance than a hammer mill. HP/ton ratio is approximately 7:1 and produces a Particle Size Distribution (PSD) that passes most state specs without screening. Cage mills handle moisture well because there are no screens or grate bars.

Hammer Mills

Final product size is typically controlled by grate bars or perforated screens, which can be high maintenance because of the many hammers and grate bars or screens to replace. The highest HP/ton ratio is approximately 10:1. It doesn't handle moisture well due to blinding of the screen/grates and it cannot handle uncrushable items.

Vertical Shaft Impactors (VSI)

Final size is controlled by rotor speed, but a VSI can't grind fine enough to pass some state Aglime specs and requires screening after crushing. HP/ton ratio is approximately 3:1 with high throughput. Moisture can cause buildup problems.

Where should I start?

Determining the chemistry of your material's Calcium Carbonate Equivalent (CCE) is the place to start. You will need to determine the amount of Aglime material required to equal one ton of pure calcium carbonate. For example; if your material is Dolomitic Limestone, with a CCE of 95, the rate per acre equivalent to Calcitic Limestone, with a CCE of 100, would be 1.05.

Testing your feed material is the next step and should determine the follow­ing: feed size (PSD), energy consump­tion (horsepower per ton per hour or kW per ton at the target PSD), wear metal estimate per ton of throughput and fin­ished product particle size distribution.

In conclusion, the production of Ag lime can be achieved in many ways, and each operation will have its own set of specific requirements that influ­ence final production. When deciding what crusher type is best for a specific operation, it is important to consider the following: local market condi­tions, state specifications, existing equipment and facilities, maintenance requirements, total power consump­tion and existing capacity, and aux­iliary capital equipment.

Agronomists in many states can help evaluate the economics of soil chemistry and how Aglime can be used to reduce fertilizer use, improve crop yields and lower costs. Some states may subsidize the use of Aglime. Contact a local university extension to learn about the use and incentives in your region.

Eric Marcotte is the Inside Sales Manager of Stedman Machine Company, based in Aurora, Ind.