Chlorophyll provides the vital interface that connects the light energy from sun to all life on earth via the process of photosynthesis.  The magnesium atom is at the centre of a chlorophyll molecule; without it photosynthesis would not be possible. It is like the plug on the end of an extension lead, and it plugs all life directly into the suns energy.  Magnesium plays a similar role in plants to that of iron in the structure of haemoglobin in animals.

Managing plant growth is about managing photosynthesis.  The more energy from the sun the plant can collect, the more it will yield.  Any limiting factor that inhibits maximum photosynthesis is one that will limit crop productivity.

Look for luxury levels of magnesium in leaf analysis. It is vital for photosynthesis and phosphorus uptake; the energy system of the plant.  You can apply as much nitrogen as you like, but without adequate magnesium you will receive poor photosynthetic responses.

Magnesium is:

  • essential for the metabolism and translocation of carbohydrates
  • an enzyme activator, and a cofactor in synthesis of amino acids and proteins.
  • included in beta-carotene, a precursor to conversion to Vitamin A.
  • required in many enzymatic reactions for metabolism of compounds.
  • found in fruit and vegetables, and the body converts magnesium to vitamin A when required.
  • abundant in antioxidant properties.
  • important as an anti-cancer agent and in reducing parasites on stock, e.g. fly strike, Barbers Pole Worm and many others.
  • often the missing link for hypomagnaseamia (grass tetany) or downer cows. 

Magnesium reacts with phosphorous to enable phosphate compounds (Magnesium ATP) to be carried around the plant; particularly helpful in translocation of phosphorus into seeds of high oil content and for superior seed germination.

Ca:Mg percent is the most important relationship in soil fertility.  Light soils will require more magnesium than heavy soils. This is due to the properties of the magnesium atom which are much smaller than Ca and aids in the tightening of the soil structure to prevent excess leaching. Required at 10.1-12% of base saturation, but should be up to 20% in very light soils.

Magnesium has more impact on soil pH than Calcium due to its smaller atomic size (more surface area available to alkalise soil).

Calcium, magnesium, potassium and sodium are all alkaline cations and the more of these ions instead of hydrogen and alminium, the more balanced the soil will be. Magnesium can be easily leached, so magnesium deficiencies are more pronounced on acid and coarse textured soils. If low levels are present, use a combination of slow and quick release forms to ensure availability for the duration of the crop, e.g. Dolomite and Kieserite. The base saturation is made up of a combination of predominantly calcium, magnesium, potassium, sodium, and hydrogen. Any significant increase or decrease in any of these elements can ultimately increase or decrease magnesium base saturation.

After decades of using serpentine and its blends on the soil, why do we still have widespread magnesium deficiencies?

Dolomite is a magnesium and calcium carbonate combination that raises pH and soil magnesium levels and is very useful when both magnesium and calcium are required.

Magnesium carbonate, (Mag 2000) increases pH when magnesium but no calcium is required.

Magnesium oxide is created by the burning of magnesium carbonate to drive off CO2 has the highest concentration of all Mg fertilisers. Thermal alteration dramatically affects the reactivity of magesium oxide since less surface area and fewer pores are available for reaction with other compounds. Serpentine, a hard silica rock is also ineffective at raising soil magnesium, unless applied at very high rates, or is applied to very acid soils.

Magnesium sulphate is a good source when both magnesium and sulphur are needed, and can be used at the reproductive phase.

Defoliation can occur if magnesium is deficient while carrying a heavy crop. Monocots (grasses including sugar cane, cereals, maize, bananas) leaves’ can become striped; often along the full length, resulting in necrosis in the tip of the leaf. As maize plants age they have a more spotted appearance. It is relatively easy to build magnesium in the soil, but not so in the plant. We would like it to be 50 ppm, but realistically it is often less than half that figure; more often than not it is below 10 ppm. That may not be due to low magnesium, rather than low sulphur. Building sulphur may not solve it either. Calcium may be the key in this situation.

Magnesium is quite mobile and is translocated from older leaves to younger leaves under normal conditions, and is particularly obvious when there is a deficiency in the soil. 

Magnesium - the Unheralded Star  

Magnesium - by Neil Kinsey        

Dr. Linus Pauling, winner of two Nobel Prizes stated: "In my opinion, one can trace every sickness, every disease and every ailment to a mineral deficiency."

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Magnesium deficiency in maize

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Magnesium deficiency in potatoes

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