Diagnosing Magnesium Deficiency in Fertilizer-Responsive Crops

Magnesium is considered a macronutrient even though it’s needed in small amounts. That’s because it’s critical for photosynthesis, protein synthesis, and enzyme activation.

Very little attention has been paid to magnesium (Mg). With high-yielding fertilizer-responsive crops it’s becoming the limiting nutrient in crop productivity.

For more information on the importance of magnesium for optimum crop health and nutritional profile see Magnesium: The Forgotten Element .

Symptoms of Magnesium Deficiency

Leaf chlorosis is one symptom of magnesium deficiency that most farmers and ranchers are aware of, but there are three disorders associated with Mg deficiency:

1. Decreased root structure
2. Leaf chlorosis on mature leaves
3. Reduced yield and crop quality

If you diagnose Mg deficiency by leaf chlorosis, you’ve already lost optimum crop production. (1)

Discovering Nutrient Deficiencies in Early Stages

Soil testing is critical for detecting nutrient deficiencies before your crops take a hit. But testing alone is not sufficient. Just because nutrients are in the soil doesn’t mean they’ll make it into the plants. There are a lot of factors that go into soil and plant health.

You’ve looked at the soil test, and you had the lab test for magnesium and other micronutrients, right? What does that soil test tell you about the soil pH, CEC, and presence of other cations? Look particularly for aluminum and calcium, these compete with Mg for plant uptake. You need all three in balance.

Now it’s time to walk your fields and see what the situation is. Certain soil types tend to have magnesium deficiency more than others. Clay soils bind Mg so less is leached away. Sandy soils and acidic soils are often Mg deficient. (2)

Physical Signs of Magnesium Deficiency

Before you see any above-ground plant nutrient deficiency symptoms you need to pull a few plants and look at the root structure. Plants absorb magnesium primarily through their roots. When the root structure is diminished, so is the plant’s ability to come into contact with needed nutrients.

Most magnesium makes it into the plant through mass flow, the movement of Mg2+ (the ionic form most plant-available) through the soil, past plant roots, and dissolved in soil water. The plant takes up needed water (because of respiration) and the dissolved Mg is absorbed at the same time.

If we’re in a drought year, this system isn’t very efficient. There has to be enough water in the soil.

Causes of Magnesium Deficiency

You also need to look at your fertilization program. High concentrations of Ca++ and K+ inhibit magnesium absorption. We’re back to soil balance. All these nutrients are necessary, but all in the correct proportions. Mg deficiency is often the result of an excess of another cation nutrient.

There are 2 major reasons for Mg deficiency in a field:

1. Low indigenous Mg because of the source rocks
2. Loss of Mg from leaching

Leaching of many nutrients is the result of long-term unbalanced crop fertilization programs and tillage that compacts the soil. Regenerative agricultural practices alleviate soil compaction and decrease the leaching of all nutrients.

Chlorosis of the Leaves

You know that depending on which leaves are affected, several deficiencies may need to be addressed. Mg deficiency is first seen in the older, mature leaves.

Magnesium is a very mobile nutrient in the soil and in the plant. The upside is that a plant can store Mg in older leaves until it needs it in new growth. But that movement of nutrients is also an indication that your field is experiencing a Mg deficiency for some reason.

Abiotic stresses such as drought can cause nutrient deficiencies. An overabundance of NH4 (ammonia) from spreading fresh manure will create an imbalance.?

Magnesium deficiencies show up very differently depending on the crop. Some crops are just more sensitive. Corn and sugarcane are the two most dependent on the proper Mg/nutrients balance. Soybeans come in a close third. (3)

By the time you’re seeing chlorosis on the leaves, your crop has already lost a great deal of its potential. Adding magnesium at a late stage of chlorosis will benefit the future crops in that field.

Your Yield is Lower than Average and the Quality Isn’t Up to Snuff

Not a good year. But a lesson learned. A magnesium deficiency may be the cause. A poor yield is usually the result of multiple factors. The weather, farm management practices, seed quality, disease and pest pressure all play roles.

Fields with a deficiency of magnesium or an imbalance of nutrients may not show any symptoms but will be less resilient to drought, flood, or excessive heat. If yield is your only metric, deficiencies will continue to be a problem. It’s hard to balance all the nutrients necessary for a resilient, high-nutrient profile, high-yielding crop.

Transitioning to sustainable agriculture is the long-term solution. But how do you handle income for the farm in the short term?

We recommend Q-Bio Magnesium 3.0% to our clients who have magnesium-deficient soils. With precision agriculture, you can apply Mg supplements exactly where needed. Q-Bio Magnesium is certified organic so it is beneficial for a transition to a higher quality premium crop.?

This year, crop input costs are through the roof. Corn may be sold at a loss. The USDA NRCS has programs to help offset a transition. Contact us and let’s see how we can help your farm or ranch not only survive but thrive. We’re here to support you. When soil speaks, we listen.

1. https://link.springer.com/article/10.1007/s11104-012-1567-y
2. https://www.soilmanagementindia.com/nutrient-elements-in-soil/magnesium-forms-sources-and-behaviour-soil/2806
3. https://link.springer.com/article/10.1007/s11104-012-1567-y