America's two leading field crops, corn and soybeans, yield more grain today than they did 75 years ago. But while corn has taken giant leaps forward in average bushels/acre, soybean yields have advanced in baby steps.

Between 1930 and 2003, average corn yields jumped nearly sevenfold, from 20.5 bu./acre to 142.2 bu./acre. In that same period, average soybean yields didn't quite triple, from 13 bu./acre to 33.4 bu./acre. National soybean yields have hovered around 40 bu./acre for about a decade.

Why the widening yield gap between corn and soybeans? There are many reasons, say Purdue University agronomists Jeff Volenec and Scott Jackson. Among them: genetic differences between the two crops and greater attention paid to corn research.

“We're looking at about a 0.4 bu./acre/year average increase for soybeans. For corn it's 1.5 bu./acre/year,” says Volenec, crop physiology professor. “Will soybeans equal the annual increase in corn yields in the near future? No. Can we improve on the 0.4 bu./acre/year? Yes.”

Collaborative research by crop geneticists, physiologists, agronomists and breeders could boost soybean yield potential, Volenec says. However, researchers aren't likely to increase average soybean yields more than a few tenths of a bushel in the next 10 years, and may never be able to place the oilseed on a similar yield growth track as corn.

The challenge for researchers continues to be cracking the unique genetic makeup of the soybean plant.