Calcium and magnesium Point Wise Notes For Competitive exam

CALCIUM AND MAGNESIUM

• 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