How much of today’s extra corn yield compared to what previous generations harvested is due to genetics? How much is due to improved management? A project involving Iowa State University and Bayer was designed to find out.

“We worked closely with Bayer, and it is a great example of public and private research collaboration,” Sotirios Archontoulis says. The Iowa State agronomist headed up the project, which spanned three years, incorporating numerous research studies plus data on Bayer hybrids stretching from Ohio to Nebraska. Tony Vyn, a Purdue Extension agronomist, helped guide the study.

“We looked at data from 82 hybrids split between 103-day and 111-day maturity,” Archontoulis explains. “Year of release stretched over 40 years, from the early 1980s into the 2020s. We looked at over 200 plant traits — everything from grain yield to roots.”

40 years of hybrids: Learning from results

Archontoulis points to these findings:

Yield gain per year. Yield gain for 111-day hybrids averaged 1.96 bushels per acre per year, compared to 1.67 bushels per acre per year for 103-day hybrids. Researchers determined that early- and late-maturity hybrids took different paths to higher yields. The grain yield components, namely individual kernel weight and total kernel number, have increased at different rates depending on relative maturity. Full-season hybrids achieve higher yield through longer duration of grain fill. Modern early-maturity hybrids exhibit a higher grain growth rate vs. older early hybrids.

Harvest index differences. “Harvest index is an important measure of plant performance,” Archontoulis says. It is the ratio of grain to total dry matter; the higher the ratio, the higher the percentage of total production going into grain. “Higher harvest index ratios for today’s hybrids are due to genetics and not management,” he says. “Increased harvest index alone accounts for about 15% of higher U.S. corn yields today versus 40 years ago.”

Plant density vs. genetics. Genetics account for about 86% of the yield increase, and higher populations account for about 14%. Bob Nielsen, Purdue Extension corn specialist, now retired, determined there was little yield difference at populations ranging from 28,000 to 35,000 plants per acre.

Biomass production. Newer hybrids produce more total biomass. At the R2 stage, about 20% of the increase is due to genetics, and 80% is from higher populations. By R6, a shift occurs to about 42% due to genetics and 58% from higher plant density.

Changes in leaves. Modern hybrids produce the same number of leaves but close the canopy faster. Today’s plants silk earlier and start grain fill earlier, too. Leaf angle is about 6 degrees more erect, but that trend is leveling off. Archontoulis notes only a small correlation between leaf angle and yield.

Root system differences. Newer hybrids grow roots faster and deeper. For every new leaf produced after V5, root depth increases 3 inches. Genetic gains in root mass are 10 times lower compared to yield gains, with a large environmental effect on roots. About 84% of total root mass today is within the top 2 feet.

Grain quality. Management significantly affects grain quality, Archontoulis says. The percentage content of protein, phosphorus, potassium and sulfur per bushel is lower in grain today. Yet total amount produced per acre of all these nutrients is higher today.