Is Magnesium The Missing Link?

Compelling reasons to take a good look at Mg levels in your soils and methods of raising them
Written by Jon Williams from

The result of over 700 detailed soil samples in West Wales has consistently shown a shortage of magnesium with 70 per cent of the soils depleted on the clay colloid and 48 per cent showing a shortage in the available form, and unless we carry out a detailed soil analysis this major nutrient deficit cannot be corrected. Here we consider some of the possible reasons how we have come to this situation in UK soils. For the last 70 years we have focused on PH, available P, K, Mg and the fertiliser industry placed great emphasis on the P and K without consideration for the Mg (Ref Kirkby and Mengel 1976). There is now increasing evidence of the occurrence of magnesium deficiency symptoms showing up in crops and plants which will affect crop yield and quality. [1]

Soluble Mg fertiliser is a recent discovery

One of the reasons for this was that there was no soluble magnesium fertiliser available in the UK until 30 years ago when bulk powdered Keiserite Mg So4 arrived from a mined source of naturally occurring rock from Germany.

However this was difficult to spread and sales of this soil amendment product did not take-off until a granular version arrived 20 years later, but still no manufactured compound fertilisers made in the UK contained Magnesium. Today Keiserite, magnesium sulphate and Magnesia Kanit 27%Na 11%K, 5% Mg, 12%S are available in the UK and both are approved for organic farms with derogation but there are still no compound fertilisers containing magnesium.

The role of Magnesium

Magnesium has a key role in the formation of chlorophyll and acts as the anchor for Nitrogen in every cell of chloroplast both of which help to create the dark green colour we associate with a healthy plant. However its major role is in enabling the phloem of the plant to easily transfer the products of photosynthesis, sugars down into the roots. A magnesium deficiency results in a plant with excessive leaf growth in relation to root growth and the sugars stuck in the leaf which makes the plant very light sensitive and reduces the potential of the plant to transfer Co2 via sugars to the roots and hence to the soil. As a main component of Chlorophyll it has a key role in the production of ATP the energy storehouse of the plant and activates more enzymes in the plant than any other nutrient. So magnesium is both a structural component of chlorophyll and needed for its bio-synthesis. 

Soil analysis methodology

To make an accurate assessment of soil levels of magnesium as well as the other major nutrient calcium a detailed soil analysis is of paramount importance for a healthy aerobic living soil and good major nutrient balance and the important ratio of Ca/Mg established by Dr William Albrecht A healthy soil needs to have a total of 80 per cent of the clay colloid dominated by these two nutrients with the ratio being dependent on the soil texture for example a heavy clay soil having 68 per cent calcium and 12 per cent Magnesium. The detailed analysis will also provide the CEC (Cation Exchange Capacity), organic matter content and sulphate levels as well as the percentage sand, silt and clay content and so can be used as a management tool to bring balance and harmony to the living eco system which is the soil.

How to amend the soil levels?

The soil amendments of these major nutrients are based on the liming agents either Calcium Carbonate or Dolomitic limestone depending on the results found on the clay colloid and what the soil texture is in any particular soil. Where the levels of calcium and magnesium are low Dr Albrecht stated that the liming agent needs to be applied in volume as with bulk lime. Raising the levels of these two major nutrients will optimise soil microbial life. However where levels are nearer to the optimum and for farmer convenience and easier spreading granular versions of these products are now available and so they can be used on an annual basis to keep soil levels at optimum for maximum yield continuously instead of letting levels drop and making amendments of these major nutrients every five years or so as was the practice in the past.

However the situation on many farms is that Calcium levels are good and Magnesium levels low or very low. The only option in these circumstances is to provide essential magnesium using Keiserite Mg So4. When the Calcium levels fall the soil will need both calcium and magnesium, at which point it will benefit from the Ca and the Mg in Dolomitic lime which comes with a ratio of 2 parts Ca to 1 Mg. It must be noted that Keiserite supplies Magnesium in a soluble form and so will not build soil reserves on the clay colloid which is needed for optimum soil health.

Essential points to note

Ensuring that magnesium is at the optimum level for your soil type will enhance the availability of phosphorus and in particular locked-up phosphorus. Over 90 per cent of soil tests show P at very high levels. The shortage of magnesium may well be what has brought this situation about in the soils of West Wales. Releasing this phosphorus will increase the Brix index of the plant (sugar level) resulting in the plant having greater frost resistance and therefore a longer, more productive growth phase in every season. A detailed soil sample which guides us to the correct levels of these major nutrients is essential for efficient nitrogen use. This results in a reduction of the environmental impact of applying synthetic nitrogen fertiliser resulting in lower costs for the farmer and an environmental benefit: a win-win situation.

Magnesium has a key role in the enzyme activity in the plant affecting 800 enzymes and has a similar role in the human body affecting 300 different enzymes including enzymes that bring about the phosphate transfer into ATP production. It can be termed as the key that starts the whole engine!!

It is all about balance

Excess Magnesium (Mg) will reduce the aerobic level of the soil and can lock-up Manganese (Mn) which can lead to Take-All in Wheat and too high a PH created by excessive levels of these two nutrients, Calcium and magnesium can reduce the availability of copper and zinc as well as manganese. Magnesium is particularly important in the reproductive growth phase ensuring optimum fruiting of the plant. It particularly benefits the growth of legumes. Magnesium uptake is usually between 10 and 25 Kgs per hectare per year, which is a similar amount to sulphur.

Magnesium constitutes 50% of the plant’s protein level as the result of holding the Nitrogen in the leaf. Understanding the essential need for the adequate supply of magnesium in sucrose translocation is highly relevant for sugar beet and fodder beet production. Magnesium uptake can be inhibited particularly in acid sandy soils with high aluminium levels as well as hydrogen and manganese ions. High plant magnesium levels are needed in drought conditions or in soil with high potassium levels. The balance between potassium levels and magnesium levels is best in equilibrium in the soil. With excessive use of nitrogen under stressed conditions a magnesium deficiency can occur and research still needs to be carried out to find out why. 

A shortage of magnesium in the crop can be amended by a foliar feed after flowering to boost seed formation and fill but is best repeated every 5 weeks. It is still not known to what extent magnesium status of crops must be raised to counter stress events which will undoubtedly increase with global warming. [2] as magnesium ensures a balanced plant with good root formation to support the above ground plant material.

So magnesium can only be considered as being a major nutrient for optimum soil and crop performance and I suggest that we all take steps to monitor this nutrient for the more efficient use of nitrogen and to maximise carbon sequestration in the soil by carrying out a detailed soil sample using the Albrecht philosophy developed after 36 years of soil science research.

The benefits for human health of adequate magnesium in the diet are such that we can boost our energy levels, have a clear mind, reduce stress, and with the stress related impact of the current health crisis yet to be assessed from the effects of lock-down and social isolation it is certainly highlighting the benefits of adequate magnesium in the diet. Research is suggesting that half the UK population are deficient and so the overall benefits to the well-being of the health of the people is paramount and farmers have the responsibility to ensure soils have adequate magnesium if they are to be considered custodians of the soil, the environment and the people they serve producing quality food for the nation.

[1] Institute of Integrative and comparative biology at the University of Leeds

[2] Cakmak and Kirkby 2007

This article includes information from a conference organised by the International Potash Institute and the International Fertilise Society and Sabanca University in Cambridge, UK on Dec 7, 2007