NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
September 9, 1999
North Dakota State University soil scientists evaluating methods to reduce iron chlorosis problems in soybean fields made one discovery in a time-tested scientific way--by accident.
The mishap occurred while seeding soybean test plots in 1998. By mistake, one plot was not seeded and the next plot received double the planned rate of seed. The soybeans in the plot with the high rate of seeding showed much less chlorosis and were more vigorous than adjacent plots.
The unseeded test plot may not go down in history with Alexander Fleming's noticing a mold that killed bacteria in a discarded culture dish, leading to the discovery of penicillin. But it does provide some insight into cultural control of iron chlorosis.
According to soil scientist R.J. Goos, it has been suspected for some time that iron chlorosis is more severe in soybeans grown in narrow rows rather than traditional 30-inch rows. Apparently very high seeding rates in 30-inch rows can reduce chlorosis even more.
"We were intrigued by the observation, but thought that it might be a fluke," Goos says. "In 1999 we compared three seeding rates in 30-inch rows, 25, 50 and 100 pounds per acre, or about 75,000, 150,000 or 300,000 plants per acre."
The benefits of the heavier seeding rate in 30-inch rows was seen at all test locations, but the amount of benefit varied from site to site. The most noticeable effects were at a site near Argusville involving Glacier, a variety susceptible to iron chlorosis. Planting 50 pounds of seed per acre in 6-inch rows or 25 pounds per acre in 30-inch rows led to severe stunting and chlorosis. There was somewhat better growth with 50 pounds of seed on 30-inch rows and almost normal growth from planting 100 pounds of seed per acre in 30-inch rows.
It isn't clear why heavy seeding rates in 30-inch rows can reduce chlorosis. High soil moisture is known to intensify iron chlorosis, so Goos speculates that with more crowded soybean plants, the root zone around the plant crowns dries out faster. Planting in 30-inch rows also allows for cultivation, which can help dry out the soil.
Goos stresses that variety selection is still the most important factor in reducing iron chlorosis in soybeans. If chlorosis is not controlled by planting more resistant varieties, growers should consider switching from narrow rows to 30-inch rows and using heavier seeding rates, he says.
If heavier seeding rates are not an option, Goos says he has seen a response from putting a half pound to a pound per acre of FeEDDHA fertilizer in-furrow or as a seed treatment with 30-inch rows. Foliar sprays of Fe-EDTA have only given a short-term effect.
Goos is conducting research sponsored by the North Dakota Soybean Council to identify varieties resistant to iron chlorosis. The variety Traill appears to be the most chlorosis-tolerant variety released by NDSU and serves as a standard to rate other varieties.
The variety Council is rated about 79 percent as resistant as Traill. Goos says varieties weaker than Council should not be grown on fields prone to iron chlorosis, such as alkaline, poorly drained soils. Other resistant varieties include Jim and Lambert. Both are rated at 87 percent of Traill.
The evaluation effort is just getting started, with a large backlog of public and private varieties to evaluate. "We hope the farmers of North Dakota will benefit from a uniform evaluation of varieties for iron chlorosis," Goos says.
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Source: R.J. Goos (701) 231-8581
Editor: Gary Moran (701) 231-7865