How to Add Calcium to Soil

Learn How to Improve Clay Soil with Calcium


By Ken Scharabok – Ensuring your soils have an adequate level of available calcium should be an essential part of your field fertilization practices for several reasons. Here’s why and how to add calcium to soil on your homestead.

• Calcium improves tilth and friability by reducing the stickiness and clinging ability of soils containing clay.

• Calcium, by breaking up clay particles and improving clay soil, increases the surface are of soils so more nutrients can be held by each particle.

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• Calcium, by loosening up soil, increases water penetration ability, water-holding capacity and aeration ability. Oxygen is required by soil life, thus the more oxygen available, the more soil life which can be supported.

• Calcium is a direct nutrient to growing plants and soil life. Among other benefits, it is essential to healthy cell walls, affecting both permeability and strength. For a grain crop, adequate calcium can help to prevent lodging as the plants reach their full height.

• Calcium acts as a buffer/carrier for some other nutrients and enhances uptake of water.

• Calcium promotes root and leaf development in plants.

• Calcium can up to double the effectiveness of other fertilizers applied, such as nitrogen, phosphorus, potassium and other essential nutrients. For example, at a low pH, phosphorus is precipitated as iron and aluminum phosphates which are relatively insoluble and unavailable. With liming, phosphorus compounds in the soil become more soluble and can reduce the amount of phosphorus fertilizer needed.

• Calcium can reduce plant blight from soil-borne pathogens.

• Calcium is a relatively immobile element within a plant. Thus, a continuous supply is essential for growing plants.

• Calcium encourages the growth of symbiotic nitrogen-fixing bacteria on legumes, and thus makes more nitrogen available to the legumes and other plants.

• Calcium can extend the life of legume plantings. Legumes are heavy users/providers of calcium. If it is depleted, stand deterioration or loss can occur.

• Calcium applied to lawns can decrease thatch build-up by promoting soil life, particularly earthworms. Although most lawns never receive calcium (e.g. periodic spreading of limestone), each cutting contains a small percentage of calcium. Thus, over time the soil under many yards can become calcium-deficient.

While available calcium is not directly related to pH levels (i.e., a soil with a high pH can be calcium deficient), its use on soils with a low pH will decrease its acidity. In acid soils, there may be an excess of soluble iron, aluminum and/or manganese, in conjunction with shortages of calcium and magnesium.

How to Add Calcium to Soil

Some garden crops, such as tomatoes, peas and beans, have a high calcium requirement but do best in slightly acid soil. In this case, calcium can be provided in the form of a gypsum soil amendment (calcium sulfate). Agricultural gypsum is a good source of both calcium and sulfur, yet has little effect on soil pH.

(A commercial crop with a major need for calcium is tobacco. The tobacco belt was established primarily for two reasons: temperate climate and naturally available calcium in the soil. While mature grain crops and grasses contain from 0.25-0.5 percent calcium; and cotton, soybeans and alfalfa plants average 2.0 percent calcium, tobacco plants contain up to 4.0 percent calcium. When this land became “tobacco poor,” it was largely due to calcium being removed faster than it could be naturally made available to the plants.)

Available calcium levels can be determined by most soil tests. Here’s how to check soil pH. However, bear in mind in most cases the calcium application rate (in the form of tons of limestone per acre) will be for the upper 6-1/2 to seven inches of soil (plow depth). Thus, additional limestone may be required for the root zone below this depth.

Calcium is normally available locally in the form of limestone delivered and spread at a cost per ton. While the limestone use in this case if for its high concentration of calcium carbonate, the actual amount of calcium in it will be in the 35-45 percent range. Dolomitic limestone and should not be used if magnesium levels are already high.

While the cost of limestone should be prorated over about a five-year period to the cost of crop or livestock production, the actual returns from increased production will often repay the cost of application in the first or second year.

The calcium in limestone will take a period of time to dissolve and become available to plants. For quick results, calcium can also be applied directly to plants in a solution. In this manner, it goes directly to plant cells rather than having to cycle through the soil.

So now you know how to add calcium to soil, so remember, when it comes to fertilization, think C-N-P-K, rather than just N-P-K.

Originally published in Countryside 2003 and regularly vetted for accuracy.


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