With many corn acres in the central Corn Belt headed into the rapid growth stage, growers are calling Ken Ferrie to report corn whorls that have yellow striping, when they should be green. Ferrie says the issue in many cases is a sulfur deficiency – or a combination of too little sulfur and zinc – even on heavier soils versus sandier soils, which traditionally have had the issue more frequently.
“We are seeing pretty substantial sulfur responses in our corn plots even at and above 3.5% organic matter,” he says. “I still believe that, in total, 3.5% organic matter soils will supply enough sulfur. The issue is those soils just don’t supply sulfur quickly enough to plants in the spring.”
As proof, Ferrie says he is increasingly seeing the “yellow sulfur whorl” in soils with 3.5% organic matter between the time corn emerges and the V8 to V10 growth range. As the corn plant gets bigger, roots go deeper and the soil gets more active. Over time, the soil will release organic sulfur and that symptom of sulfur deficiency will gradually disappear.
“But under the concept of never let corn have a bad day, corn showing a sulfur deficiency is having a bad day,” he says. “This is especially true for those G and L1 hybrids that will flex down if you stress them in that window before tassel and right after emergence.”
Make Sure To Know The Deficiency Your Crop Has
Ferrie says farmers need to make sure what they’re dealing with is a sulfur deficiency and not a lack of nitrogen.
“The main difference,” he says, is that nitrogen deficiency shows up in the bottom of the plant, but sulfur deficiency shows up in the newer growth—the top or whorl. That’s because, unlike nitrogen, sulfur is not mobile in the plant, so the plant can’t steal sulfur from older portions and move it to newer ones.”
Plants deficient in sulfur can show reduced plant development and delayed maturity.
“Anything that retards growth delays maturity,” Ferrie explains. “Sulfur-deficient 112-day corn will act like a 115-day corn; it tassels and finishes later. In other words, plants become inefficient, producing less growth per heat unit per day.”
Fall Fertility Factors Likely Play A Role This Season
In many cases, the sulfur deficiency this spring can be traced back to last fall if the grower took ammonium sulfate and DAP out of their program to reduce costs and then forgot to update their program, and add nutrients back in this spring (check out our video above on the topic).
For that reason, Matt Duesterhau, Crop-Tech Consulting field agronomist, wants to remind growers to update their corn nutrient plan for this season, if they haven’t already.
“If you kicked out the fall dry [fertilizer], are you counting on adding that sulfur in at sidedress?” he asks. “Let’s make sure we’ve got a complete plan that we’re using, to get that full rate of nitrogen we need for our target yield goal, and the sulfur to go along with it.”
Ferrie calls the process of updating fertilizer plans balancing the checkbook.
“Rapid growth is not the time to show a sulfur deficiency, because you’re setting so much of the crop yield,” he says.
Meaghan Anderson tells Iowa growers to be sure to add up the sulfur their corn crop is getting from all the various sources, like ammonium sulfate in pesticide applications and sulfur from any other fertilizer materials.
“This can help avoid unnecessary spending and luxury uptake by crops,” says Anderson, Iowa State University field agronomist for central Iowa, in her online article, Who Needs Sulfur? You Might Need Sulfur.
Evaluate And Select The Right Source Of Sulfur
Purdue research suggests 10 lb. to 15 lb. of sulfur per acre, applied just before planting but no later than sidedress, is adequate in most sulfur-deficient situations.
Duesterhaus says high-yield growers in his area (western Illinois) are having good results using 20 lb. to 25 lb. of sulfur in a corn-soybean rotation, and a little more than that in a corn-on-corn program.
Minnesota research shows an annual rate of 25 lb. of sulfur is adequate for corn production on sandy soils, while fields with more organic matter need less (10 lb. to 15 lb. per acre). The application can be done via broadcast or as sidedress.
Selecting the right source of sulfur is critical to ensure enough sulfate-sulfur is present in the soil at key uptake periods, notes Dan Kaiser, nutrient management Extension specialist at the University of Minnesota.
“Rapid uptake of sulfur occurs in corn from V5 to early silking when 50 percent of sulfur needed by corn is taken up,” Kaiser says. “Roughly 10 percent of sulfur needed by corn is taken up prior to V5, but this timeframe is still critical and deficiencies early in the growing season can limit yield – particularly in cool and wet springs.”
Kaiser reviews some considerations for sulfur sources in his online article, What source of sulfur is right for you?
Ferrie cautions growers that elemental sulfur must go through a biological breakdown to get to sulfate, and is not a good option for corn this time of year.
“This reaction doesn’t get into full swing until soil temperatures are above 75 degrees F, which means elemental sulfur doesn’t make it to the dance until later in July and August,” he says. “That is great if you still need sulfur then, but higher organic matter soils usually release enough sulfur by mid-June to take care of the deficiency issues.”
If you have sandy soils, you could need a different strategy. Sandy soils have low organic matter content and a low cation exchange capacity (CEC), making them prone to sulfur leaching. In those types of soils, Ferrie advises farmers to put together a program that keeps the corn plant supplied in sulfur all season, and not just up until V10.
Why Are We Seeing More Sulfur Deficiency?
What has occurred is less acid rain is falling today, so fields get less sulfur from the atmosphere. You can trace this fact back to the Clean Air Act of 1970. So, while it’s good that acid rain has been reduced, it has resulted in less sulfur being available for crops to tap into.
What that means now is that farmers in much of the Midwest must treat sulfur more like a macronutrient rather than a micronutrient.
“The continued drop in the soil’s ability to supply sulfur has now reached the level that we have to start thinking about applying sulfur every year ahead of corn, no matter what the organic matter is,” Ferrie says.
He adds that depending on where farmers live, the results and needs for sulfur applications can vary. For instance, growers farming downwind of a large city like Chicago may still be receiving enough acid rain to meet their crop’s sulfur needs, due to all the fossil fuel being burned on the roads and highways.
“When all the cars in Chicago are electric, then you’re going to have to join the rest of us and start applying sulfur,” he says.
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