Producers traditionally have managed iron chlorosis by using resistant varieties, he says, but the rapid turnover in improved varieties — as well as chlorosis appearing in varieties normally considered tolerant — have shown the need for other controls.

“It’s a very complex subject affected by a lot factors,” he says. “Some varieties are more tolerant to iron chlorosis than others. But varieties come and go so quickly, and sometimes it’s difficult to tell which are tolerant and which are not.

“We’ve used foliar sprays, but you have to spray each time a new leaf appears, and treatments need to go out before symptoms appear.

“Several states have tried seed treatments, with varying responses. It’s just difficult to make it work. In-furrow sprays have been attempted, and that has proven variable.”

In previous trials, iron chelates and ammonium sulfate were tested for their effectiveness in preventing and improving iron chlorosis on soybeans.

Foliar treatments after damage has been observed and have been ineffective, and most soil-applied iron applications are rapidly converted to unavailable forms or have shown inconsistent results, says Delaney.

Tests showed that ammonium sulfate had a negative effect on seed germination at most of the locations. 

And, although none of the supplements for alleviating iron chlorosis increased yield, some treatments did improve seed weights. 

Research conducted in North Dakota and Minnesota has looked at the use of an oat cover crop to take up available soil nitrogen before planting soybeans, thereby lessening the severity of iron chlorsis, says Delaney.

“Soil samples taken from problem fields in Alabama have shown a strong trend toward higher nitrate-N and soluble salts in areas where iron chlorosis was most severe.

“So a study was conducted to investigate the use of cover crops to sequester available soil nitrogen before planting soybeans on a high-pH soil field in the Alabama Black Belt, in south Montgomery County.”

One year of research showed that using a wheat cover crop for soybeans significantly lowered springtime electric conductivity, soluble salts and soil nitrate levels on the high-pH Black Belt soils, says Delaney.

It also significantly lessened iron chlorosis across varieties with different levels of iron chlorosis tolerance.

“Soil moisture was visibly enhanced under the cover crop and may have contributed to lessening iron chlorosis symptoms and increasing plant growth during what proved to be a very hot and dry summer.”

Using a combination of a cover crop and a tolerant variety had an additive effect on lowering iron chlorosis symptoms, he adds.

phollis@farmpress.com