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Corn+Soybean Digest

Thick Stands Combat Chlorosis

As soybeans have moved farther north in the North, so has the problem with iron chlorosis.

"In fields where it is bad, it's really bad," says Jay Goos, a North Dakota State University soil scientist. "The areas with chlorosis are getting bigger, too."

But Goos, who's extensively researched the yellowing soybean leaves suffering from a lack of iron, says new research may help.

If growers would boost their seeding rates and plant iron chlorosis-prone fields to 30" rows, rather than narrower spacings, those beans would see less chlorosis damage.

"Iron chlorosis is more severe in soybeans grown in narrow rows rather than in traditional 30" rows," he says.

The reasons for this aren't clear. Root zones of soybeans grown in crowded 30" rows may dry out around the crown. Cultivation also helps dry the soil. Wet, poorly drained soil seems to spur iron chlorosis on, says Goos.

In Goos' area, wheat and barley grow with no hassle from iron chlorosis. But plant soybean seed on this Northern ground, particularly if it's wet and poorly drained with high pH, lime and salt, and you're asking for yellow soybeans.

"Fields that have grown beautiful crops of wheat and barley over the years will grow soybeans that in some parts of a field get 6" tall and die," the soil scientist says.

Most North Dakota growers find it faster and more economical to use their wheat-planting equipment to drill or air-seed narrow-row soybeans.

"To suggest to farmers to plant in 30" rows and at heavier seeding rates is a bit of a new concept. Some just say 'I can't afford a new string of equipment.' Under those circumstances we say they're going to have to pick the variety with the strongest level of resistance possible," Goos says.

It takes an exceptional level of resistance, he adds. "Resistance doesn't solve the problem, but you might get 20 bu/acre of soybeans instead of 5."

Another problem: not all fields in the state are suitable for growing soybeans. Some fields are just too saline and alkaline for soybeans, Goos says. It wasn't long ago when soybeans were found mostly in the four southeastern counties of North Dakota. Today, production has spread to more than 20.

This past year, Goos compared three seeding rates in 30" rows: 25, 50 and 100 lbs/acre, or 75,000, 150,000 or 300,000 plants/acre. Three varieties were planted: Traill, very resistant to iron chlorosis; Council, a moderately resistant bean; and Glacier, which is susceptible.

The most noticeable effects were at a site near Argusville, where Glacier was planted at the three rates in both 6" and 30" rows. Soybeans planted at 25 lbs/acre were severely stunted at both row spacings. There was somewhat better growth with 50 lbs of seed in 30" rows, and almost normal growth from planting 100 lbs/acre in 30" rows.

Still, Goos first recommends using as resistant a variety as possible.

"If chlorosis is not controlled by variety selection, farmers should consider switching from narrow rows to 30" rows and using heavier seeding rates. If heavier seeding rates aren't feasible, we have seen a response to putting 0.5 lb or 1 lb/acre of FeEDDHA (an iron fertilizer) in-furrow or as a seed treatment with 30" rows."

Two foliar sprays of FeEDTA, another fertilizer, have given a response of about 4 bu/acre in Goos' trials, which is only marginally profitable at current soybean prices.

"Increasing seeding rate is no more expensive than these other options, particularly with traditional varieties."

North Dakota growers are increasingly concerned about chlorosis, Goos adds.

"Farmers are telling me it used to be, for example, that just the first 10 rods along the ditch would get chlorosis. But in recent years they tell me the bad areas are expanding. That's because it's been wetter than normal for several years in a row, and our water tables are up."

Goos' study was conducted with funding from the North Dakota Soybean Council and the Fluid Fertilizer Foundation.

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