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January 6, 2005 Review Chlorosis Scores Before Buying Soybean Seed Iron deficiency chlorosis is a common and destructive problem for soybeans. "In North Dakota, chlorosis is observed when soybeans are grown on poorly drained, high pH soil," says R. Jay Goos, a North Dakota State University Soil Science Department professor. "Chlorosis is made worse by many soil factors, so that it is impossible to say that just one factor causes it. Cold soil temperatures, calcium carbonate in the topsoil, elevated salinity, heavy rains and elevated nitrates in the soil all intensify chlorosis. However, in my experience, the most practical single soil indicator is the presence of calcium carbonate in the topsoil." Chlorosis of soybeans is a destructive problem because of the behavior of iron inside of the plant. When a crop turns nitrogen deficient, the plant can move nitrogen from the older tissue to younger tissue to help keep the growing point alive. That is why, for example, the bottom leaves of corn turn yellow with a nitrogen deficiency. Things are different with iron. “Plants have a much harder time translocating iron," Goos says. "That is why the youngest tissues turn yellow first, while the older leaves may be green. If the growing point is damaged, the crop will be severely stunted and yields will be severely reduced. Even a temporary yellowing is associated with yield losses of 20 percent, while a prolonged yellowing will decrease yields 40 percent or more.” The best way to fight chlorosis is to select a resistant variety. "We have examined many possible control measures and nothing is as effective as selection of a resistant variety,” Goos says. “Foliar sprays or soil-applied fertilizers have not given an economic or long-lasting response. The only other control measure that helps is to increase row spacing to 22 or 30 inches and to increase seeding rates to 250,000 to 300,000 seeds per acre. This is not economically feasible with transgenic varieties. But, for farmers who grow a resistant public variety like Traill or MN0302 and save their own seed, this could be feasible." Goos evaluates about 170 varieties per year for resistance to chlorosis. "The North Dakota Soybean Council has supported our chlorosis research for many years," Goos says. "We now have data on about 700 varieties.” In general, for soils that produce temporary or moderate chlorosis, Goos recommends a variety with chlorosis resistance equal to Council or Asgrow 0801 or stronger. "However, if chlorosis is severe and lasts more than two weeks, a farmer needs to plant a variety with the most resistance available, consistent with other considerations, such as maturity," Goos advises. Chlorosis scores from Goos' research in 2004 and earlier years can be found online at: www.soilsci.ndsu.nodak.edu/yellowsoybeans ### Source:
R. Jay Goos, (701) 231-8581, rj.goos@ndsu.edu |
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North Dakota State University |
