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Magnesium: Essential for Soil, Plant & Animal Health

By Paul Reed Hepperly, Ph.D. 

Although nitrogen, phosphorus, potassium and even calcium are often discussed, magnesium is mostly unheralded and misunderstood. In this article I will examine the nature of magnesium deficiency and show how ignoring soil magnesium can lead to dire consequences in human, plant and animal health.

Like the other aforementioned macrominerals, magnesium is essential for plant and animal health and productivity. In man, beasts and plants it is found in substantial amounts and can wreak havoc when it is deficient.

Our health is rooted in our soils both as vegetables we consume and as animal products, which are nourished from the soil. Since the vast majority of what we eat comes from the soil, our health partly depends on earthworm activity, but the overuse of modern chemical fertilizers and pesticides has left many soils deficient in earthworms. This in turn impoverishes the soil.

As soils lose their vibrant microbial activity they become depleted in critical nutrients even as fertilizers are applied in larger amounts. Synthetic fertilizers are not a solution and often aggravate soil issues they supposedly cure. Remedying this downward spiral is more critical than ever because a growing population needs not only more food but better food quality for present and future generations to thrive.

One cannot escape the reality that our health is a result of our farming systems, and the state of our health attests to that truth. We are a product of the food we eat, the quality of soil it is grown in and the practices we employ in its production.

corn field needs magnesium
Unlike nitrogen, phosphorus and potassium, magnesium is often overlooked in conventional fertility.

Grass Tetany: A Telling Saga

In early spring when animals first come off supplementation and onto pasture they can suffer a condition called grass tetany. In this condition animals suffer severe muscular tremors, and worse, from magnesium deficiency.

This condition is particularly frequent in pure grass nitrogen-fertilized pastures. Farmers who both selectively eliminate broadleaves and fertilize with ammoniated nitrogen alone are almost ensuring magnesium deficiency. When clovers and broadleaves are selected out in pasture management, as farmers we end up eliminating the magnesium champions; they are the first victims of selective herbicides used to control “weeds” in the pasture.

However, these plants are the solution because they contain several times the amount of magnesium of a typical high-yield grass that was favored. Concentrating on an unbalanced diet leads to an artificial magnesium deficiency.

Modern agricultural practices selectively eliminate forage diversity and selectively fertilize, deteriorating the quality of our forage and the environment. When we eliminate magnesium-rich clovers and broadleaves and concentrate solely on a single grass, we do not allow the grazing animals to have a diverse diet to satisfy their health as they do instinctively under more natural conditions. In this scenario, the farmer and the farm animals lose.

Early grass growth can be notably deficient in magnesium while legumes are several times higher in critical magnesium. Rather than count on nitrogen from the air via leguminous plants, we instead choose nitrogen from fertilizer and its unintended consequences of soil acidity and key nutrient depletion.

Magnesium deficiency of grasses such as corn and sorghum expresses as yellowing or chlorosis, particularly between the veins of plant leaves. This is most common in acid, older soils such as those predominating in the wet tropical regions such as in northern Puerto Rico. Maintaining the diversity of our pastures is essential to providing a balanced ration for grazing animals, and this is rooted in the balance of our soil resource.

In alkaline pH 7.3 or higher soil, many plants will be unable to absorb iron, leading to plant yellowing and poor performance. In the case of chlorophyll, it shares an almost identical heme structure with the substitution of magnesium for iron. Magnesium deficiency mostly occurs when soils are old, sandy in texture and acid in pH. Acidity is a key factor for nutrition and health of both plants and animals. Although plants and animals are considered separate, on the core biochemical level they are more alike than one might guess.

Soil Considerations

Know your soil pH

The acidity of soil has a major impact on optimizing essential and micronutrients. Best overall mineral availability is in a very weakly acidic or neutral soil pH (6.3 to 7.0). To optimize crop and animal nutrition, the fertility program needs to start with getting the soil pH correct.

In humid, weathered acid soil this means liming. In semi-arid and arid conditions high alkaline (pH 7.3 or higher) can cause micronutrients to become a major obstacle, and this may need acidification with sulfur. In mineralizing your farming system, start with a soil test and proceed with acidity adjustment.

Know your soil organic level

In all conditions productive natural soils are generally over 5 percent soil organic matter. Many cropped tillable soils have plummeted to 1 percent or less SOM. Farmers who want to optimize their farming systems need to be aware that the ability of their soil to provide water, air and minerals is a function of SOM, which governs soil biology and metabolism.

All farmers with less than 5 percent SOM need to consider and then develop effective practices to increase soil organic matter to optimize their results. While 100 pounds of dry soil at 1 percent SOM can absorb less than 30 pounds of water, the same soil with over 5 percent soil organic matter can absorb over 200 pounds of water. Since minerals can only be absorbed through water, not only is the state of organic matter critical for moisture levels, but also for mineral nutrition. The leading cause of crop loss is drought, but without SOM optimization our crops are unnecessarily jeopardized and demineralized.

  1. Total testing — Take a comprehensive soil test that includes both macro and micronutrients, and make the necessary adjustments to achieve balance.
  2. Make amends — Develop a remediation of toxicities and deficiencies found in soil and/or plant tissue assays.
  3. In the case of magnesium, when the soil test is under 100 ppm for magnesium any liming should be done with dolomitic limestone (CaMg(CO3)2 ) rather than calcitic limestone which has little or no magnesium. A dolomitic limestone should contain at least 2 percent magnesium, and the effect of lime will be best when finely ground.

Take care to lime only to pH 7 as over-liming will result in severe micronutrient deficiency. In acid soils pH 5.7 will be sufficient to eliminate aluminum and manganese toxicity.

  1. Trace elements — Such as iron, zinc, manganese, boron, molybdenum and others have enormous impacts on plant and animal health. As someone who has worked on thousands of soil and plant analyses it is seldom that no insufficiency or excess is found. These can be overcome but only through diagnosis and directed action including consulting experienced and knowledgeable professionals.

Widespread Deficiency

In a 2012 USDA nutritional report, it was found over 57 percent of males and females do not get the recommended minimum daily amount of magnesium in their diet. Scientists have also argued that the magnesium minimum dosage has been set too low. They suggest that just about everyone would benefit from upping their magnesium level by about three times the current estimate. It is important we get this right. Magnesium can lead to devastating health results such as: excitability, muscle cramps, headaches, apathy, confusion, insomnia, heart irregularity and thyroid disruption.

Magnesium governs over 300 biochemical reactions by playing important roles within enzymes. Researchers point to the tandem of low dietary intake and high refined sugar as the deadly duo driving deficiency of this critical element in humans.

Modern use of potassium as a key fertilizer, when not coupled with adequate magnesium, contributes to unbalanced nutrition from the food we eat. Additional causes of rampant magnesium deficiency may include stress and pharmaceutical drugs such as hypertension drugs which lower magnesium dramatically.

Magnesium Revelation

Unlike nitrogen, phosphorus, potassium and even calcium, magnesium is seldom considered in conventional fertilization programs. Just because we choose not to focus on it does not mean that our lives do not depend upon it, whether we know it or not. How we farm and the status of our food system, which is soil-based, can make the difference between health and disease; yet we are sometimes uninformed about these choices.

Synthetic chemical fertilization, often touted as a solution to our agriculture and food woes, represents a dangerous double-edged sword. Instead of boosting nutrients they can play anti-nutrient roles. After synthetic ammoniated nitrogen, potassium salts — muriate of potash or potassium sulfates — are the leaders in global fertilizer use. Unfortunately, although potassium can raise yield and sugar content, it can also play an antagonistic role in reducing magnesium and calcium.

This artificially induced depletion reduces the accumulation of these critical minerals, contributing to deficiency and disease.

Iatrogenic is a Greek word conveying the idea that curative practices or treatments can sometimes cause harm. In simple terms, the treatment causes malady. Without proper knowledge and management, nutrient imbalance becomes the norm. When balancing nutritional needs, a broader view and diversity must be valued if we are to remedy some of our nutritional issues rooted in unbalanced diets. For example, heavy application of ammoniated nitrogen is a key promoter of blossom end rot, a problem of calcium deficiency.

To improve our present situation we need to change our values. Our health will improve with soil health improvement. We need to address nutrition from the ground up and should not ignore the environment and health costs of the food system itself.

Plants & Animals Reflect the Soil

At my old experiment station the research plantings of sorghum would completely fail in some spots. The soil was an old weathered soil (Oxisol) notable for good physical condition, but it had a low mineral salt nutrient level. Very notable in this soil was an inability to detect measurable amounts of magnesium, and this was particularly acute in the spots where sorghum would not grow. This is not a coincidence. The issues were resolved by adjusting pH and amending with magnesium.

I was assigned to diagnose the same problem I ended up having in my own body. Magnesium deficiency, not tachycardia in my case, was the core root in both instances. All in all, this was a difficult but effective way to learn that soil and health are interrelated.

When we optimize one factor in isolation we often cause artificial imbalance and disruption of other critical factors. Through our so-called treatment we can induce unnecessary chronic mineral havoc. This is in fact what we have done in our industrialized, centralized agricultural food system. Our nutritional status is literally grounded in balanced nutrition from soil, and we can consciously improve this as farmers, gardeners and consumers by becoming good Earth stewards and making better management choices.

Editor’s Note: This article appeared in the November 2015 issue of Acres U.S.A. magazine

About the Author

Paul Reed Hepperly, scientist, consultant, educator and advisor, previously served as the research director for Rodale Institute (2002-09). His son, Reed Paul Hepperly, is CEO of Hepperly Enterprises, a premium compost supplier and developer of tropical root crops in Mayaguez, Puerto Rico. Paul currently resides in Maryville, Tennessee. Contact him at paul.hepperly@gmail.com.


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