Calcium and magnesium Point Wise Notes For Competitive exam

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• In plants, calcium is present as calcium pectate which is a constituent of the middle lamellae of the cell-walls.

Calcium is considered essential for the growth of meristematic tissues and to the functioning of the root tips.

• Calcium is absorbed by plants as Ca2+ ion. This takes place from the soil solution and possibly by root interception or contact exchange from the exchange sites.

• The only nutrient which might be supplied completely by interception is calcium, although the process may provide a significant part of the requirement for Mg, Zn and Mn.

• The quantities of calcium required by the plants can be readily transported to root surfaces by mass flow in most soils, except highly leached and unlimited acid soils.

• Quantities of magnesium taken up by plants are usually less than calcium and potassium.

Anorthite is primary source of calcium.

Augite and hornblende also contains calcium.

• Among the secondary minerals, calcite (CaCO3) is the dominant source of calcium in soils of semi-arid and arid regions.

Dolomite (CaMg (CO3)2) may also be present in association with calcite and gypsum (CaSO4.2H2O) in arid regions.

• Usually Ca is the cation of the highest concentration in the soil in both soluble and exchangeable forms for soils high in pH>8.0.

Ca2+ concentration of the soil solution is frequently about 10 times greater than that of K+, its uptake is usually lower than that of K+.

• Capacity of plants for uptake of Ca2+ is limited, because it can be absorbed only by young root tips in which the cell-walls of the endodermis are still unsupervised.

Two soil calcium minerals having the maximum solubility are calcium sulphate and calcium carbonate.

Calcium sulphate usually occurs only in arid soils where the sulphate concentration in solution exceeds 0.01 mol/L.

• Calcium is abundant in leaves and its normal concentration ranges from 0.2 to 1.0%.

• Calcium is well known for its role in cell division and cell elongation.

• Calcium deficiency leads to diseases such as bitter pit in apple, blossom end-rot in tomato, black head in celery, internal browning in Brussel’s sprout, blossom end-rot of pepper and cavity spots in carrots.

• Plants generally use Ca in amounts lower than N and K but higher than P.

• Most of the acid soils in India are deficient in calcium.

• Under high rainfall and in soils with low base saturation, Ca leach down from the root rhizosphere and the soils become deficient in Ca.

• Soils containing less than 25% of cation-exchange capacity or less than 1.5 cmol (p+) Ca per kg soil considered as Ca-deficient.

• In acid soils, application of Ca through liming increases the availability of P to crops.

• Plants generally take up Mg in smaller amounts than Ca.

• For optimum growth, plants require a ratio of exchangeable Ca : Mg very close to 6.

• Plants grow well and meet their Ca and Mg requirement in soils with Ca:Mg ratios varying from 1:1 to 15:1.

Liming materials commonly used for amelioration of acid soils are the oxides, hydroxides, carbonates and silicates of calcium and magnesium.

• In chlorophyll, magnesium as the central atom is bound to N atoms of 4 porphyrin rings by 2 covalent and 2 coordinate bonds.

• Content of magnesium in plant ranges between 0.15 and 1.00% of the dry matter in leaf tissue.

• Magnesium deficiency results in interveinal chlorosis of the leaf, in which only the veins remain green.

• In cotton, due to magnesium deficiency lower leaves may develop a reddish purple cast, which gradually turns brown and finally becomes necrotic.

• Availability of P is more in soils having pH 6.5-7.5.

Calcium in soil mostly moves through the process of root interception.

• The liming material commonly used for acid soils is calcium carbonate.

Dolomite is source of both calcium and magnesium.

• Interaction effect of calcium with phosphorus in acid soils is synergistic.

• Calcium content in CaCO3 is 100%.

• The neutralizing value of CaO is 179, Ca(OH)2 is 136, CaMg(CO3)2 is 109, CaCO3 is 100, CaSiO3 is 86.

• Magnesium element dominates the cation-exchange capacity in soils derived from serpentine rock.

Tetany disease of cattle is mainly attributed to magnesium deficiency.

• The common extractant used in most soil-testing laboratories in India for estimation of calcium and magnesium is Neutral normal ammonium acetate.

• Serpentine (MgSiO3) contains 26% Mg.

Leaching loss of Mg is lower than calcium.

• Calcium requirement of dicots is more than monocots.

• Presence of high concentration of K+, NH4+ or Ca2+ ion on soils restricts the uptake of Magnesium.

Triethanolamine (TEA) buffered at pH 8.25 has been generally used for measurement of exchange acidity.

Over liming leads to boron deficiency in acid soils.

• Calcium and magnesium are present in soils in three different forms as mineral, exchangeable, solution form.

• Many crops respond to calcium application when the degree of calcium saturation of the CEC falls below 25%.

• Soil is considered as ideal one when ratios of cations is as follows

Ca : Mg = 6.5:1

Ca : K = 13:1

Mg : K = 2:1

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