Iowa Farmer Today
07-21-07
Mineral deficiency cropping up in alfalfa fields
By Tim Hoskins, Iowa Farmer Today
CRESCO -- The solution to some pale-looking alfalfa plants could have been as
easy as “S.”
Jeff Ryan, who farms in Winneshiek County, noticed in 2006 selected areas of
his hay field had a pale color and
didn’t produce nearly as well as other areas of the field.
However, Ryan started by ruling out what could not be the reason for the
paleness in his crops. He ruled out plant establishment because it was not a firstyear field.
“It didn’t show up in the new establishment,” he said.
Ryan was able to rule out a deficiency of other nutrients due to field conditions.
He then worked with Brain Lang, Iowa State University crop specialist for
Northeast Iowa, to solve the problem, which turned out to be sulfur deficiency.
Lang had seen similar problems throughout his area. He suggested Ryan send
alfalfa samples to test for sulfur levels.
At the moment, there is no reliable soil test for sulfur, said Lang and John
Sawyer, ISU fertility specialist.
“This is unique because a soil test does not help us,” said Lang.
Sawyer says sulfur deficiency in alfalfa is a combination of several factors:
Alfalfa needs more sulfur than do corn and soybeans. Alfalfa requires double the
amount of sulfur as corn, and corn needs twice more sulfur as soybeans to grow,
Lang explains.
Due to the switch to burn low-sulfur coal and the installation of scrubbers on coalfired power plants means there is less sulfur is in the air.
Fertilizer companies have taken sulfur out of their fertilizer.
Lang says most of the sulfur deficiency is being found in soils with low organic
matter or in fields that didn’t have manure applied.
“It is a combination of all those factors,” said Sawyer.
Lang says crop paleness is a generic symptom of various nutrient deficiencies. It
is the key sign that would indicate sulfur deficiency.
Sending in plant samples would be the key. Lang told Ryan to send in some of
samples of healthy-looking plants to compare with pale plants.
Ryan dried out the plant samples on a cookie sheet before sending them to a lab.
He noticed the sulfur-deficient plants were not as large as the healthy-looking
plants.
One solution to sulfur deficiency is to a sulfur fertilizer. However, that only would
help alfalfa for the current season.
Sulfur deficiency also is starting to show up in corn. However, more research is
needed on determining critical values for corn.
In corn, sulfur deficiency presents another twist to a possible solution. Plant
samples should be taken when the root system is complete, so there could be
sulfur in the soil.
However, the root system is not complete until plant is near tasseling. That
means by the time the plant sample is taken, it likely is too late to take corrective
action for that year’s crop.
It would be a good indication for future sulfur levels.
In alfalfa and hay crops, there is time to take corrective action.
Ryan noticed the sulfur deficiency about his first cutting.
After the results came back, he was able to apply 100 pounds per acre of
ammonium sulfate. The cost of the application and material was about $17/acre,
Ryan estimates.
The alfalfa crop responded, and his tonnage improved on his cuttings for the rest
of the year.
This year, he said he noticed some paleness in the same areas. However, it was
not as bad as last year.
Ryan again applied ammonium sulfate.
“It is not going to be a cure-all in one shot,” Ryan said.
Because he has some grass mixed in his hay crop, Ryan said the nitrogen in the
ammonium was also able to boost that part of his crop as well.
Ryan said there is no premium for selling sulfur-deficient hay, such as some dairy
farmers pay for potassium-deficient hay.