Soil Nutrient management
Calcium and Magnesium
Forms of Calcium and Magnesium Taken up by Plants
Plants can only absorb the ionic forms of calcium (Ca2⁺) and magnesium (Mg2⁺) from the soil solution and as exchangeable Ca2⁺ and Mg2⁺ on soil colloids. The amount and relative proportion usually reflect the soil's parent materials.
Calcium and Magnesium Deficiency in Plants
Calcium is not usually a limiting nutrient. Symptoms of calcium deficiency first appear on younger leaves and tissues, growth is inhibited, and plants have a bushy appearance. The youngest leaves are usually small and misshapen with brown chlorotic spots developing along the margins, which spread to eventually unite in the center of the leaves.
The deficiency of magnesium is much more common than that of calcium, at least when the soil pH is at an appropriate level. Magnesium is highly mobile in the plant and deficiency symptoms first appear on the lower, older leaves.
Calcium and Magnesium Toxicity in Plants
Toxicity from excess calcium or magnesium is rare because plants do not accumulate these nutrients even when they are present in soil at levels far above that required by the crop. Most of the problems caused by excess soil calcium are the result of secondary effects of high soil pH.
Management of Soil Calcium and Magnesium
The calcium to magnesium ratio is merely a statement of the relative proportions of available calcium and magnesium in the soil. It does not give any information about the actual levels of these elements. For example, if there is 4.88 meq of calcium in 100 g soil and 1.72 meq of magnesium in 100 g soil, then the calcium to magnesium ratio is 2.8:1 which might be considered too low. For those that subscribe to the calcium to magnesium ratio, the suggested ratio range is 5:1 to 8:1 for maximum crop yields.
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