The Effects of Calcium on Soil

Soil pH

• Calcium affects the pH value of your soil in several ways. Soils with high levels of calcium typically have an alkaline pH, while soils that are low in calcium have an acid pH. When the pH value of the soil is above 7.2, the soil loses its ability to absorb calcium. The excess calcium found in these alkaline soils combines with other elements in the soil to form insoluble compounds that are difficult for plants to absorb. Plants automatically regulate and restrict their calcium intake from the soil within a narrow range, limiting the benefits of increased soil calcium levels for plants.

Chemical Interactions

• When the level of calcium in the soil exceeds the capacity of the soil to absorb it, it binds with other elements in the soil. This process forms insoluble compounds that are difficult for plants to absorb. Excess amounts of calcium restrict the availability of several elements that are essential for healthy growth in plants. The elements affected by excessive calcium levels include phosphorous, boron and iron. Large quantities of sodium, magnesium, aluminum, ammonium or potassium can also limit the ability of plants to absorb calcium from the soil.

Calcium Solubility

• In highly acidic soils with a pH below 7, the iron and aluminum cations in the soil become more soluble. These elements combine with the calcium in the soil, restricting its availability for plants. Since acidic soils are typically low in calcium, plants growing under these conditions are often subject to calcium deficiencies. Adding calcium to the soil in the form of calcium carbonate or gypsum will increase soil pH, the level of calcium in soil and the ability of plants to use that calcium.

Alkaline Solubility

• Soil with a high pH contains unused calcium that combines with other chemicals in the soil. Calcium often combines with phosphorous and boron, preventing plants from absorbing them under these conditions. Excessive amounts of phosphorous or boron in the soil result in stunted growth and discoloration of the leaves. In soils where the levels of phosphorous or boron are at toxic levels, applying calcium will prevent these chemicals from damaging plants.