Soybean yield curve is up, but why?

When you look at the historical data, it is clear that there is a long upward trend in the yield of soybeans over the last 80 to 90 years.

What researchers would like to know is more about what kinds of changes have driven those increases, and what plant breeders can do to continue — or ideally accelerate — that trend.

At the annual Kansas Soybean Expo in Topeka on Jan. 11, Kansas State University soybean breeder Bill Schapaugh talked about some of the many projects going on across the country to get answers to those questions.

“A wide array of genetics has been developed in public and private programs since 1920 and there have been huge strides in the improvement of varieties,” Schapaugh said.

He shared preliminary results of a project at the University of Illinois that looked at the progress that has been made in disease resistance, one of the drivers of better yields.

Key Points

• Soybean research projects attempt to unlock the secrets of yield increases.

• Yield improvements are part genetic and part farming practice.

• The research is funded by the Kansas Soybean Commission.


“Plant breeders and plant pathologists have made significant progress in breeding for resistance to a whole host of diseases,” he said.

The K-State portion of the research is looking at the physiological changes that have occurred that may help drive yield, he said. That research includes examination of pollen germination, chlorophyll concentration in leaves, canopy temperature and spectral reflectance of the canopy, a measurement of “green-ness” that builds on the “green-seeker” technology used to manage fertilizer decisions.

Several interesting trends have already been identified, Schapaugh said.Trials have been done on dryland soybeans as well as those under irrigation.

“Obviously our results this year were affected by the drought that resulted in no harvest of soybeans in most of Kansas,” he said. “But what we did find is a consistent trend of upward yields that amounts to about a quarter-bushel to a third of a bushel per year over 70 years.

“We also discovered that the ability of genotypes to cool themselves has improved. Canopy temperatures have dropped over time with new varieties being several degrees cooler with the same moisture of previous varieties.” Cooler translates to better tolerance for heat, a better photosynthetic rate, and a more active seed fill — all of which mean better yield.

The changes in yields appear to be about half driven by improvement in genetics and the other half by advances in production systems, such as a movement to no-till farming, fungicide applications and seed treatments, and better planters that provide more consistent and accurate seed set.

“Part of our work is separating it out and trying to look at genetics and what we can learn that will help us do a better job in the future,” Schapaugh said.

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RESEARCH LEADER: Bill Schapaugh, a soybean breeder at Kansas State University, is one of the scientists working on a nationwide project that attempts to understand the forces that drive increased yields in soybeans.

This article published in the February, 2012 edition of KANSAS FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.