Calcium

Calcium is essential for many plant functions. Some of them are

·   Proper cell division and elongation

·   Proper cell wall development

·   Nitrate uptake and metabolism

·   Enzyme activity

·   Starch metabolism

Factors Affecting Ca Availability

·   Soil pH: Acid soils have less Ca, and high pH soils normally have more. As the soil pH increases above pH 7.2, due to additional soil Ca, the additional "free" Ca is not adsorbed onto the soil. Much of the free Ca forms nearly insoluble compounds with other elements such as phosphorus (P), thus making P less available.

·   Soil CEC: Lower CEC soils hold less Ca, and high CEC soils hold more.

·   Cation competition: Abnormally high levels, or application rates of other cations, in the presence of low to moderate soil Ca levels tends to reduce the uptake of Ca.

·   Alkaline sodic soil (high sodium content): Excess sodium (Na) in the soil competes with Ca, and other cations to reduce their availability to crops.

·   Sub-soil or parent material: Soils derived from limestone, marl, or other high Ca minerals will tend to have high Ca levels, while those derived from shale or sandstone will tend to have lower levels.

Sodium(Na+): High levels of soil Na will displace Ca and lead to Ca leaching. This can result in poor soil structure and possible Na toxicity to the crop. Conversely, applications of soluble Ca, typically as gypsum, are commonly used to desalinate sodic soils through the displacement principle in reverse.
Phosphorus(P): As the soil pH is increased above pH 7.0, free or un-combined Ca begins to accumulate in the soil. This Ca is available to interact with other nutrients. Soluble P is an anion, meaning it has a negative charge. Any free Ca reacts with P to form insoluble (or very slowly soluble) Ca-P compounds that are not readily available to plants. Since there is typically much more available Ca in the soil than P, this interactions nearly always results in less P availability.
Iron(Fe++) and Aluminum(Al+++): As the pH of a soil decreases, more of these elements become soluble and combine with Ca to for essentially insoluble compounds.
Boron(B-): High soil or plant Calcium levels can inhibit B uptake and utilization. Calcium sprays and soil applications have been effectively used to help detoxify B over-applications