Early in the growing season, Richard Wurtzberger began to notice a strange occurrence in his southern Minnesota corn fields: The leaves were yellowing at the tips.
The fields had ample nitrogen, so Wurtzberger was confused. He called in his independent crop consultant, Steve Commerford of New Ulm, Minn., who diagnosed the problem as sulfur deficiency.
"I was surprised because no one ever talks about sulfur problems around here,” Wurtzberger says.
It's true that for decades, soil fertility research in the Corn Belt rarely noted sulfur deficiency in soils. Agronomists credit years of rainfall that deposited sulfuric acid into the soil for helping keep sulfur levels high.
Now as pollution controls reduce the acid rain problem and higher yields demand more organic matter, sulfur is becoming more limited, says Dan Froehlich, agronomy manager for Mosaic Crop Nutrition.
"When farmers were content getting 150-bu. corn, organic matter could supply the sulfur readily,” Froehlich says. "Now with 180-bu. corn, it takes 8 lb. to 10 lb. more sulfur to produce those yields.” An 180-bu.-per-acre corn crop needs about 25 lb. of sulfur, he adds.
Know what to look for. Unless a farmer really knows what to look for in sulfur deficiency, it can easily be misdiagnosed as nitrogen
deficiency, Commerford says.
Both nitrogen and sulfur deficiency cause the plant to yellow, he says. The primary difference with sulfur deficiency is that yellowing shows up after the crop is initially very green.
"Sulfur does not readily translocate in the plant, so older leaves will remain green and the newer leaves will become yellow,” he adds.
Commerford realized sulfur was becoming a problem when he saw unusual symptoms in high-yield environments where nitrogen was not a concern, such as fields with manure applications. He noticed green streaking in these fields along wheel tracks, and he began doing side-by-sides of sulfur and nitrogen in these fields.
- Late Spring 2009