Magnesium’s impact on plants:
Magnesium is a secondary macronutrient that is essential for plant life, playing a significant role in soil structure, and physical condition. Even minor magnesium deficiencies will weaken a plant, making it susceptible to many ailments. However, a major plant magnesium deficiency will cause significant stress that will eventually cause plant decline. Toxic effects from excessive magnesium in the plant are rare but will cause devastating challenges in the soil playing a decisive role in plant strength.
Unlike nitrogen, phosphorous, and potassium the plant has smaller demand for magnesium. This is why many growers tend to ignore it. Also, magnesium deficiency is hard to diagnose. Many of the visual symptoms do not appear until the plant is in major decline, the deficiency usually leading to disease, insects, and/or other environmental stress factors.
Magnesium plays only a small role in the plant’s primary structural development, but in my opinion, it is the most important nutrient for all secondary metabolic functions. Chlorophyll develops in the early stages of the plant life cycle, and magnesium is the center of this life-sustaining plant blood. Consequently, if magnesium is deficient in the plant the first link in the chain of secondary metabolic function is compromised. Secondary metabolic functions are responsible for producing oxygen, toxins to fight off plant attacks, and also to nourish sugars, acids, proteins, just to name a few. All of which keep plants healthy and to feed the soil bacteria once a plant does expire.
Think about it this way… If you have a long chain holding up a storage bend and you keep adding weight to the bend, that’s added stress to the chain. If the top link is weak, the added weight is going to give way and the entire bend is going to come crashing down. The weaker the chain, the faster the bend is going to crash.
Magnesium deficiencies weaken a plant’s ability to accomplish secondary metabolic functions. Such as, producing natural protection compounds that prevent and heal them from fungal, viral, and bacterial diseases. Therefore, the first visual symptom of a magnesium deficiency may be the disease itself. If the magnesium deficiency is not diagnosed, a grower can get caught up in an endless cycle of spraying expensive fungicides on a preventive program.
Magnesium’s impact on soil:
Excessive magnesium in soil reserve will cause devastating effects to the soil’s structure, creating a lack of flow and buildup of water forming saturated soils. Magnesium is a small molecule with two positive charges. If one positive charge attaches to one soil particle, and the other positive charge attaches to a second soil particle, there will be less space for oxygen to move and will be pushed out altogether. Excess magnesium in the soil will also have a harmful impact on the uptake of other nutrients, further weakening plant health and immunity to life-threatening entities.
What may be difficult to understand is that if the soil has excessive magnesium, the plant can still be deficient. If you have this situation, then you will be playing a constant balancing act with the plant. This balancing act may require constant monitoring to assure plant and soil health.
Saturated soils commonly contain low levels of soil oxygen. Low levels of oxygen reduce beneficial bacteria, root mass, and a plant’s ability to survive any form of stress. Poor root structure hinders the uptake of all nutrients, which compromises both primary and secondary metabolic functions of the plant. Put simply, proper amounts of magnesium is a plant’s best friend, but excessive levels in the soil are a plant’s worst enemy.
Unfortunately, for those of you who have excessive levels of magnesium in the soil it may be exceedingly difficult, and costly to remediate the problem.
Review of Magnesium Facts:
- Magnesium is a secondary nutrient that is needed for several functions in the health, and growth of the plant.
- Magnesium is considered a secondary nutrient, not based on importance but the amount needed within the plant.
- Magnesium is the center of the chlorophyll molecule, like how iron is the center of the hemoglobin molecule in humans.
- Soils that contain high levels of magnesium will cause the soil to be saturated as magnesium pulls, and holds soil particles tightly together.
- Magnesium deficiencies enhance plant pest attacks.
The Function of Magnesium in the Plant:
- Magnesium plays a role in several enzymes reactions, without magnesium plants cannot produce chlorophyll which is needed in photosynthesis.
- Magnesium assists to pull several anions into the plant such as nitrate, phosphorus, chloride, and sulfur into the plant.
- Magnesium plays a significant role in sugar synthesis, oil, and fat formation, starch translocation, as well as iron utilization.
Magnesium Uptake by Plants:
- Magnesium is taken up in two different methods by the root system, diffusion, and passive uptake.
- The concentration of magnesium must be higher in soil solution for diffusion to occur. Passive uptake (mass flow) is driven by the transpiration process.
- Foliar fertilizer applications can bypass natural uptake functions with chelators such as sugars, amino acids, and complex carbohydrates to help the leaf tissue absorb magnesium into the leaf.
Magnesium Deficiency Symptoms:
- Magnesium deficiency starts with mottled chlorotic areas developing in the interveinal tissue.
- In some cases, it can superficially resemble potassium deficiency.
- Many plant diseases and pest attacks are a symptom of magnesium deficiency.
- Magnesium deficiencies may occur when the following factors affect its availability:
- Sand: Magnesium deficiencies can occur in sandy soils, low in organic matter.
- Soil pH: Magnesium availability is decreased in low pH and high pH soils.
- Soil Temperature: Low soil temperatures, and long periods of cool, cloudy weather.
- Drainage: Poor drainage causes saturated soil, which can also be accelerated by high levels of magnesium.
- Antagonists: Soils high in levels of calcium, potassium, sodium, and iron can cause magnesium deficiencies.
- Magnesium toxicity in plants is rare.
- Issues associated with excess magnesium in soils are limiting the uptake of calcium, phosphorus, potassium, iron, and manganese.
In closing, Magnesium’s impact on overall plant health is cause for careful consideration. Magnesium deficiencies weaken a plant’s ability to accomplish secondary metabolic functions. Neglecting to diagnose magnesium deficiencies can cause long term and irrefutable damage to your plant. Endless cycles of spraying expensive fungicides are avoidable with the right fertility program.
Written by Mike Hamilton, CCA & President of Turf Dietitian.