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Published June 29, 2010, 02:20 PM

Yellow beans may mean less green

FARGO, N.D. — Wheat, corn and sugar beet crops generally are looking good in Minnesota and North Dakota’s Red River Valley, but a remarkably high number of soybean fields are turning yellow with an iron deficiency that could cut yields.

By: Mikkel Pates, Agweek

FARGO, N.D. — Wheat, corn and sugar beet crops generally are looking good in Minnesota and North Dakota’s Red River Valley, but a remarkably high number of soybean fields are turning yellow with an iron deficiency that could cut yields.

Hans Kandel, an extension agronomist at North Dakota State University in Fargo, says it appears that there is a lot of iron chlorosis around. Soybeans in the Red River Valley have turned yellow because of the cooler, wetter conditions. It isn’t clear yet whether the crops can snap out of it and produce top yields.

“We really have had a kind of a cool spring and are running a bit behind on growing degree days,” Kandel says. “With the excessive moisture, most of the plants have been under some stress.”

Yellow bean leaves means less green chlorophyll that is used for photosynthesis to make a crop.

Kandel says there is no real fix to the problem, at this point.

“The first thing would have been to get a more (chlorosis-) tolerant variety in the field. We can’t change that now, because it’s in the field,” Kandel says. “But we can look to the future. If we have fields that are prone to iron chlorosis, we can pick varieties accordingly.”

Land that farmers identify as chlorosis-prone should be farmed accordingly in the future, Kandel says.

“I suggest that farmers pay attention, map the areas and be more careful in the future for selecting varieties there,” he says.

Managing chlorosis

Most soybean varieties in the North Dakota Variety Testing Program are scored specifically for how prone they are to iron chlorosis, he notes. Jay Goos, an NDSU soil scientist, has done testing where varieties are exposed intentionally to fields prone to iron chlorosis.

“Cool soils that are high in soluble salts, carbonates and nitrates contribute to iron chlorosis expression in the crop,” Kandel says. “That’s aggravated by wetter, cooler soils.”

To manage soybeans on chlorosis-prone fields, Kandel advises planting the tolerant varieties and then planting rows a bit wider apart and then putting seeds closer to one another in those rows.

“Some farmers have experimented with products that contain iron, which helps to a certain extent,” Kandel says. “We can’t really be conclusive whether this is of financial benefit. We’re still experimenting with that.” The iron supplement would have had to be placed with the seed to have an effect.

Initially, seeds use iron that is available in the seed until the single-leaf stage, but the yellowing appears as they make a new leaf. As the plant develops. the root system can develop to take up iron from the soil.

How will the chlorosis affect yields?

That depends. Several years ago, Kandel ran a field trial with a susceptible variety. In one field, a susceptible variety yielded a paltry 10 to 30 bushels per acre, but the same variety yielded a respectable 25 to 33 bushels on a less-susceptible field.

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