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Weather impacts soybean yield trend in 20-year study

 

By MATTHEW D. ERNST

Missouri Correspondent

 

ST. LOUIS, Mo. — A research project covering 12 Corn Belt states reported more heat and less rainfall impacted soybean yield trends from 1994-2013. If that trend persists, it makes localized field management more important than ever, according to agronomists.

Agronomists at the University of Wisconsin looked at soybean yield differences in this region and, accounting for yield trend impacts from soybean genetics and production practices, they determined temperature and rainfall variations impacted soybean yield trend by about 1/10 of a bushel per year.

"The recent climactic warming appeared to favor soybeans in northern states, but suppressed yields in the central Midwest," said Shawn Conley, who co-authored the study and presented its findings at the Wisconsin Corn and Soy Expo.

Conley said the greatest negative yield trend impact, from weather, came in Missouri and Ohio. Minnesota, Wisconsin and South Dakota all saw yield boosts from warmer temperatures during the time period studied. He emphasized the study measured weather impacts on yield trend.

There were exceptions to the north-south divide. Temperature and rainfall lowered soybean yield trend in North Dakota, while weather variability boosted Mississippi soybean yields by about 0.4 bushel per acre annually during the 20-year period, according to the researchers.

Iowa, Illinois, Indiana, Ohio and Arkansas were other states where there were negative yield trend impacts, according to the research, published in the scientific journal Nature Plants.

Sky is not falling

 

Emerson Nafziger, University of Illinois agronomist, reviewed and contributed data to the Wisconsin project. He cautioned the research should not unsettle producers.

"It can tie people up in knots a little bit," he said. "But you still have to manage in anticipation of good yields and not try to out-guess the weather. Short-term variability in the weather has always been the (management) rule and will always be the rule."

Wisconsin’s Shawn Conley said one implication of his research is for plant breeders to improve soybean heat stress tolerance during July and August. "Planting dates or soybean maturity groups could be adjusted to avoid the sensitive reproductive development stages of the crop that currently occur in August," he explained.

At the farm level, production practices could help reduce risks from high temperatures. Some Corn Belt soybean growers could benefit from cover crops that help manage excessive soil warming and water evaporation, according to Conley.

This season, with input costs steady and grain prices lower, producers should focus on the things they can control, said Nafziger. He emphasized selecting varieties that perform well in one’s soil types. That goes for corn, as well as beans.

Last year’s bumper corn crop could make it tempting for some producers to select high-yielding hybrids that may not tolerate heat stress in their particular region. "We never know enough about what weather is coming, so we try to (select hybrids) in medium ranges that don’t compromise yield," he said.

In corn, yield trends may be best evaluated during the period reaching back to 1960, according to a U of I report. Agricultural economists Scott Irwin and Darrel Good said yield trend suggests a national yield of 164 bushels per acre for this season. That is 2.8 bushels lower than the yield forecast last week by the USDA, which based its forecast on yields beginning in 1988.

Irwin’s and Good’s report, published on the farmdoc Daily blog last week, reiterated yield unpredictability. "Regardless of which trend projection is considered, there is, as usual, large risk of deviations from the projection," they wrote.

"For example, we estimate there is roughly a 1-in-10 chance of the U.S. average corn yield falling below 150 bushels and a 2-in-10 chance of yield rising above 170 bushels. It’s no wonder that weather forecasters are in such high demand."

Nafziger said both the Wisconsin soybean study and the Illinois analysis show crop producers should stick to the basics. "If we do management well, we’re going to put inputs on that won’t cut us short if we get good conditions, and won’t cost us the farm in a bad year," he said.

3/5/2015