December 6, 2001

NDSU Scientists Compare Soybean Chlorosis Ratings

Soybean varieties differ greatly in their resistance to iron deficiency chlorosis, according to Jay Goos, soil scientist at North Dakota State University.

"We have tested many control measures for chlorosis, including seed treatments, foliar sprays, variety selection and seeding rate. The most important thing a farmer can do to fight chlorosis is to plant a resistant variety," Goos says.

This past year, at four field sites, Goos compared the chlorosis resistance of 181 public and private soybean varieties. "The differences were striking," Goos says, "Under the same conditions one variety will be dark green and growing well, while the next variety was yellow and dying. Unfortunately, over half of the varieties we tested were very susceptible to chlorosis. This is why variety selection is so important. Most varieties for sale today will turn yellow and have reduced yields on alkaline soil."

Goos says that after variety selection, switching from solid seeding to 30-inch rows and increasing the seeding rate is the second-most effective control measure. "Switching to 30-inch rows and increasing the seeding rate to at least 250,000 seeds per acre also significantly reduces chlorosis, but this would only be practical for farmers who have row crop equipment and who are also using lower-cost seed sources. However, it is the last resort with regards to chlorosis. If a farmer plants a very

resistant variety like Traill in 30-inch rows at 250,000 seeds per acre, and still has chlorosis problems, the field probably isn't suitable for soybean production at all."

A complete report of this year's results, and the relative chlorosis resistance of 181 varieties, can be found on Goos' web site (www.soilsci.ndsu.nodak.edu/yellowsoybeans). Goos' studies are supported by the North Dakota Soybean Council.

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Source: Jay Goos, (701) 231-8581,rj.goos@ndsu.nodak.edu
Editor: Gary Moran, (701) 231-7865, gmoran@ndsuext.nodak.edu