
You can expect your corn to be about a growth stage behind and your soybeans to have less than optimal nitrogen fixation if following a cereal rye cover crop. Although cereal rye may offer soil health benefits and weed suppression, it can lead to sulfur deficiency in both corn and soybeans that follow.
“Cereal rye has a high carbon content, which can immobilize sulfur, thus causing sulfur deficiencies and low sulfur availability in a succeeding corn crop,” says Dan Quinn, Purdue University Extension corn specialist.
Shaun Casteel, Purdue Extension soybean specialist, shares that those same negative effects also are observed in soybeans. Additionally, pushing earlier planting dates in soybeans can exacerbate the issue.
“If we’re pushing planting dates, and that’s one thing I want to do on soybeans, those soils tend to be a little cooler and wetter,” Casteel says. “We’re not going to get much mineralization from just the normal organic matter fraction of it. So, we’re stuck with a situation where we could have sulfur supply issues.”
Solutions in soybeans
Casteel documented a few situations where soybeans following cereal rye yielded 6.5 bushels per acre less than soybeans with no cover crop treatment. However, those yield hits could be prevented with sulfur treatment, Casteel says.
“We’re able to bring that back,” Casteel says. “So, if anyone wants to bring cereal rye into their system, you can manage that potential sulfur immobilization and still yield just as well.”
Sulfur affects nitrogen fixation in soybeans, so sulfur deficiency leads to poor fixation. You should not apply a nitrogen fertilizer, Casteel says. It is not going to pay. Rather, applying sulfur should help boost nitrogen fixation.
Casteel recommends applying soluble sulfur fertilizers such as pelletized gypsum or ammonium sulfate up to six weeks ahead of planting to within a few weeks after planting. Simply put, you will want about 20 pounds of sulfur per acre to overcome any potential sulfur immobilization. This translates to 115 pounds of gypsum per acre or 83 pounds of ammonium sulfate per acre.
Prevent problems in corn
Corn typically will show signs of nitrogen and sulfur deficiency following cereal rye, Quinn says. Give your corn following cereal rye a boost by applying a starter fertilizer to reduce early-season nutrient stress.
“I tend to lean toward more of an application before or at planting due to when the sulfur deficiency in corn often begins to become evident when following cereal rye,” Quinn says. A rate of 15 to 20 pounds per acre of sulfur at or before planting should be sufficient. However, you can make an application at V3 through V5 if you miss that window at planting.
Quinn recommends broadcasting ammonium sulfate or gypsum. You also could make a banded application of ammonium thiosulfate (ATS) to mitigate problems. The ATS did not recover all the reduced yield following cereal rye, but it did help keep yields on par with corn that did not follow a cover crop.
“We still weren’t able to make up the yields we had without cereal rye, but we did get a yield increase,” Quinn says.
Additionally, plan to terminate your cereal rye about two to three weeks before planting corn.
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