As recently as the late 1960s, scientists believed that soybean yields maxed out at around 70 bu/acre. They had to adjust their thinking when yield contest winners started to log yields up to 100 bu/acre.

High-yielding producer plots convinced university researchers they needed to start their own maximum yield trials. Lodging proved to be an initial yield barrier, which led to the development of semidwarf varieties and shorter, more lodge-resistant, indeterminate varieties.

Row spacing and seeding-rate trials increased yields as well. "Consistent yield increases of 20% were obtained when the row spacing was reduced from 75 cm (30") to 17 cm (7") and the seeding rate adjusted to prevent lodging," says Ohio State University's Dick Cooper. "At lower yields the yield response to narrow rows is smaller and less consistent. Testing in a maximum yield environment revealed the potential for solid-seeding to increase soybean yields."

That's the real value of maximum yield research, says Cooper. "It permits the identification of yield-limiting factors that may be masked by other yield-limiting factors in traditional experiments conducted at lower yield levels," he says.

(Richard Cooper, Ohio State University)