March 29, 2001

Even a Little Yellowing Cuts Soybean Yield

Soybean growers in the upper Midwest are familiar with the symptoms of iron deficiency chlorosis, which starts as a yellowing of the soybean plant, most common on high water table soils.

"Sometimes the crop greens back up, and sometimes it doesn’t," says Jay Goos, soil scientist at North Dakota State University. "What many farmers want to know is, how much yield is lost when a crop turns yellow?"

Goos says the most detailed study on the subject was done at Iowa State University about 20 years ago. Scientists there rated chlorosis of young plants on a five-point scale, with 1 being normal plants and 5 being severe chlorosis. They estimated that yields were reduced 20 percent for each unit of chlorosis on this scale. Compared to normal soybeans, slight yellowing was correlated with a 20 percent yield loss, moderate yellowing with 40 percent loss, and so on.

Goos reviewed his chlorosis data from North Dakota for the past three years and found his results were much the same.

"We found that seed yields were strongly correlated to chlorosis at the fifth or sixth trifoliate leaf stage. The relationship isn’t too much different than that reported by Iowa State 20 years ago," he says.

The stronger the chlorosis at this stage of growth the worse the yield. Almost all of the nine sites included in this comparison produced soybeans that appeared to recover at later stages, but yields were still reduced, says Goos.

Goos recommends that producers do not push their luck on fields prone to chlorosis. "Most seed companies have both conventional and transgenic varieties that are resistant to chlorosis. Plant the strongest varieties on fields known to produce yellowing," he says.

Goos has posted his data on the relationship between chlorosis and yield, as well as chlorosis ratings of many public and commercial soybean varieties, on a Web site ( www.soilsci.ndsu.nodak.edu/yellowsoybeans ).

These studies have been 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