Second(ary) to None: Magnesium’s Underrated Role

Long before a farmer is a farmer, or an agronomist is an agronomist, in an elementary school classroom, each is taught a steadfast truth about growing things: Light is required.
Kurt Woolfork

Curt Woolfolk, M.S.

Sr. Manager, Crop Nutrition Technologies

It’s light, after all, that is turned into the energy a plant needs to grow strong — and yield high.

In short, light is required for chlorophyll and the process of photosynthesis to make energy for a crop. But what is at the core of chlorophyll? The answer isn’t (likely) the subject of elementary school lessons, but nonetheless plays several imperative roles in plant growth, not the least of which is to ensure a productive photosynthetic process.

As one of three secondary macronutrients (along with calcium and sulfur) required for balanced crop nutrition, magnesium (Mg) plays a critical role in various functions within the plant, and can have a substantial effect on plant growth and yield.

“Although magnesium is a macronutrient, it’s typically not a nutrient that is top of mind when looking at balanced crop nutrition,” says Curt Woolfolk, Manager of Crop Nutrition Technologies for The Mosaic Company. “Similar to potassium, we are finding situations where plant-available Mg in the soil may not be keeping up with crop demands, challenging us regarding the best ways to supplement this nutrient and increase yield.”

Four Critical Reasons to Pay Closer Attention to Magnesium
Magnesium is a vital team player that works with other nutrients to achieve photosynthesis within the plant, and therefore, top-profit crop production.

“The combination of an adequate supply of magnesium, along with potassium, has shown great crop protection against solar radiation, high temperatures and drought stress,” explains Woolfolk. “Whenever magnesium is applied, crops hold up better to the dog days of summer, and the result is higher yields.”

Key Considerations for Magnesium Fertilization

Magnesium is somewhat mobile within the plant, and is typically translocated from older to younger tissues, so Mg deficiencies usually appear first in older leaves. Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant (i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses. When Mg deficiencies are severe, reddening of the leaf tissue can occur.

Some of the crops demanding the highest amounts of Mg in North America include corn, potato, sugarcane and sugar beet. Among them, magnesium deficiency is a growing concern, especially in intensive cropping systems, in which high amounts of Mg are taken up by the crop. Because removed Mg is typically not replenished annually, intensive cropping systems can deplete soil Mg reserves over time.

“Higher plant populations require more nutrients to meet crop growth needs. Greater removal of magnesium from the field also occurs due to increasing yields and fewer fertilizer sources adding magnesium back into the system.”

Acidic and/or coarse-textured soils are most likely to experience Mg deficiency. Low cation exchange capacity in sandy soils can cause Mg to leach through the soil profile, especially where excessive precipitation or irrigation is received.

Magnesium is taken up by the plant as the Mg²⁺ ion. It can be found in soil solutions, on clay surfaces and within clay layers. Mg on clay surfaces (exchange sites) becomes soluble when displaced by another cation present in the soil solution. Some research suggests that repeated use of fertilizers high in cations (other than Mg) can displace this nutrient on exchange sites (cation exchange capacity), and may induce Mg deficiency.

Using a fertilizer containing magnesium, potassium and sulfur, such as K-Mag®, can minimize, or even eliminate, the risk of magnesium deficiency in plants. K-Mag supplies the right amount of each nutrient to each plant, achieving proper crop growth and development as well as increasing yield.

For more information on what K-Mag can do for your operation, talk to your local retailer or visit K-mag - Overview.

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