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Keep an early eye on zinc in corn

One out of balance micronutrient could have big growing season impacts for corn.

Raney Rapp, Senior Writer

June 3, 2024

3 Min Read
Zinc Deficient Corn
Zinc deficiency significant enough to impact yield is typically identifiable by looking closely at corn plants from root to leaf. These corn plants are showing signs of zinc deficiency in an LSU Extension research plot. Raney Rapp

A first-generation trial at Louisiana State University’s Macon Ridge Research Center is drawing attention to the delicate balance of nutrients within the soil profile and identifies solutions to address year-to-year variability.

Field conditions for corn at the Macon Ridge Center were near ideal for growing good corn and for viewing and addressing the early stages of a significant zinc deficiency.

“This is my first year starting this trial and the pH of the ground is near 7- that’s very ideal for showing a zinc deficiency,” said LSU Extension specialist Rasel Parvej said. “If the pH goes higher – a 7.5 or 8 ideally - we might see a more vigorous deficiency.”  

As pH rises, micronutrient availability goes down. While micronutrients have a deceptively small name, their impacts on yield and overall plant health can be profound, especially for producers applying specific blends of fertilizer.

“Especially the producers that use in-furrow 10-34-0, that can induce a zinc deficiency,” Parvej said. “If the pH is high, the phosphorus binds with zinc to become zinc phosphate and can make both nutrients unavailable.”

In an ideal pH of 6 to 6.5 zinc availability should not be a problem, even when applying a fertilizer with phosphorus. Field conditions in early 2024, when temperatures in the Midsouth were slightly cooler than average at the beginning of the growing season, also could have kick-started a zinc issue in some fields.

“This year was a very ideal year because it also happens with cold temperatures when plants cannot grow fast, zinc and phosphorus is highly immobile in soils, so the root needs to get to that zinc or phosphorus,” Parvej said. “When the plant doesn’t grow, it doesn’t take up that zinc or phosphorus, which is why we often see that phosphorus induced zinc deficiency when it is cold.”

Nearly 50% of zinc accumulated by the corn plant is acquired by the silking or R1 stage of growth. Identifying and correcting zinc deficiency early in the growing season can be critical to keep the issue from impacting yield.

Scout first

Zinc deficiency significant enough to impact yield is typically identifiable by looking closely at corn plants from root to leaf.

“With zinc deficiency, we start at the bottom of the leaf and it’s kind of faded in color,” Parvej said. “It will look like a white stripe, but it’s actually light green starting at the base of the leaf.”

Sulfur and zinc deficiency look very similar, but zinc is more prominent, starting from the base of the leaf and extending completely to the tip, while sulfur deficiency is often a shorter streak with less visual contrast.

Soil testing is another good diagnostic for zinc availability and uptake. Knowing precisely how much zinc is available in the soil, as well as the soil pH, can help corrective applications of fertilizer containing zinc be more precise.

Test and apply

If a soil test has already been completed and zinc shows room for improvement, application of fertilizer with the right quantity of zinc, early in the growing season is the key to avoiding yield limitations.

“If your results fall below 1 ppm or two pounds per acre, you definitely put out some zinc. It’s very responsive,” Parvej said. “The University of Arkansas is doing lots of research with zinc and they can find more than 10 bushels to 15 bushels yield increase with zinc fertilization.”

If soil tests at 2.5 ppm or 5 pounds per acre zinc, there’s no need to apply more. Soil testing is important to diagnose whether extra zinc should be applied, and subsequently applying the right concentration of the micronutrient.

“It comes back to what fertilizer the producers use for zinc,” Parvej said. “They usually use 30-0-0-2-.1 - 30 is the nitrogen, double 0 means there is no phosphorus or potassium, 2 is the sulfur and .1 is the zinc. It’s good to have some zinc in your fertilizer, but if you are putting out .1 – how much zinc are you actually putting out?” he answer is less than 1 pound per acre. Parvej said simply shifting the fertilizer makeup to include 1% zinc rather than .1 % could quickly and significantly address any zinc availability issues in the corn field.

Read more about:

Nutrient Management

About the Author(s)

Raney Rapp

Senior Writer, Delta Farm Press

Delta Farm Press Senior Writer

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