Calcium is an essential component of soil. When deposited in the form of lime, it cannot be used by plants. To combat this, carbon dioxide produced by plants reacts with water in the environment to produce carbonic acid. Carbonic acid is then able to dissolve limestone, enabling the release of calcium ions. This reaction is more readily available with smaller particles of limestone than it is with large pieces of rock due to the increased surface area. When lime is leached into soil, calcium levels inevitably increase, both stabilising pH and enabling calcium to mix with water to form Ca ions, thus making it soluble and accessible to plants to be absorbed and utilised by the root system. The calcium ions travel up the xylem of the plant alongside water to reach the leaves. The plant can utilise this calcium in the form of calcium pectate to stabilise cell walls and provide rigidity. Calcium is also used by plant enzymes to signal growth and coordinate life-promoting processes. Additionally, the release of calcium ions enables microorganisms to access phosphorus and other micro nutrients with greater ease, improving the soil ecosystem drastically thus indirectly promoting plant growth and nutrition.
Inevitable plant and animal death results in the return of calcium contained within the organism back into the soil to be utilised by other plants. Decomposing organisms break them down, returning the calcium back into the soil and enabling the cycling of calcium to continue. Additionally, these animals and plants are eaten by other animals, similarly continuing the cycle. It is however important to note the modern introduction of calcium into the soil by humans (through fertilisers and other horticultural products) has resulted in a higher concentration of calcium contained within soil.