Forms and Functions of Magnesium in Plants

September 14, 2023 Agric4Profits

1. Amount and Functions of Magnesium in Plants

Magnesium is absorbed by plant roots as divalent cation, Mg²⁺; and the concentration in tissue is between 0.1 to 0.4% similar to the range of phosphorus, calcium, and sulphur in plant tissues. The functions of magnesium in plants could be listed as follows:

Magnesium is a constituent of chlorophyll accounting for about 2.7% of cthe hlorophyll molecule.

Mg is a co-factor, an enzyme activator, in reactions associated with ATP formation (Phosphorus metabolism), phosphorylation reaction, and subsequent transfer of phosphate.

It is required to activate a number of other enzymatic systems in plant tissue such as carbohydrate metabolism, citric acid cycle in cell respiration, oil synthesis in oil palm, groundnut, sunflower, and soyabean.

Mg performs structural role in plants linking together the subunits of ribosomes.

Due to its structural role in the cell wall, Mg is immobile in the cell wall but mobile in other parts of the plant such as its presence in cell vacuoles where it controls the ionic strength of the cell.

Due to its moderate mobility in plants, symptoms of Mg deficiency appear on lower older leaves as interveinal chlorosis whereby only the leaf veins remain green. There are deep-green veins against a yellow background in a leaf.

There is a reddish pigmentation necrotic condition of older leaves of maize and oat due to chlorophyll deficiency.

Plant levels of nutrients generally have implications on human and animal feeding. Plants and grasses low in magnesium can cause grass stagger called hyper magnesium disease in animals that are fed on those grasses.

Mg- Deficiency in Nigeria occurs in acid sandy soils and sedimentary zones. Soils low in cation exchange capacity and organic matter are likely low in Mg. Mg-deficiency in oil palm is called oan range frond.

Up take of Mg is inhibited by high rates of K⁺ and NH⁺₄. This is called ion antagonism which can occur in oil palm, tree orchard, tomato, and tobacco on sandy soils.

2. Soil Magnesium and Fertilizer Materials

Exchangeable magnesium which is available for the immediate use of the crop is between 50-500kg ha^-1 in soils.

The primary sources of unavailable Mg in soils are biotite, Olivine (Mg Fe Si₃0₄) which is dominant in serpentine soils, amphiboles, pyroxene, and dolomite (CaCO₃ Mg CO₃) used for liming acid soils.

Vermiculite is the most important secondary mineral supplying Magnesium in soils. Magnesium behaves like Ca; it can move into interlayer spaces of clay minerals to become non-exchangeable. Leaching of Mg²⁺ follows the same pattern as Ca²⁺.

In serpentine soils, Mg. is dominant. Generally, in most soils, 40-80% of exchange sites are utilized by Ca²⁺ while 10-15% are utilized by Mg²⁺. Materials containing Mg are:

Dolomite (Ca, Mg)₂ (CO₃)₂ contains 13% Mg
Sulpo mag K₂SO₄. 2Mg SO₄ 12% Mg
En Mag (+K) or M NH₄ phosphate can also be applied as a spray. Epsom salt (magnesium sulphate) MgSO₄. 7H₂0
MgO (not sufficiently soluble) 55% Mg
The En Mag (+K) also supplies N, P, and K. It is a slow-release fertilizer produced in Aberdeen, Scotland. In the early SOs, this fertilizer was used extensively for flowers and shrubs at the Seaton Park near Hillhead Students Hostels, University of Aberdeen.