"While many studies have tested corn response to nitrogen fertilizer, there has been limited information on corn hybrid performance in nitrogen-deficient environments," Shanahan says.

The nitrogen treatments in the study were standardized to five rates as a percentage of university economic optimum recommendations (from 0 to 130 percent), applied to corn in continuous production as well as corn in rotation with soybeans and positioned on the same plots from year to year.

"As expected, corn yield increased with increasing nitrogen rates in both continuous corn and rotated corn and decreased with reduced rates," Shanahan says. "But what's interesting is that across all tested nitrogen rates, the average yield was higher for corn in rotation versus continuous corn by 33 percent or about 45 bushels per acre."

Furthermore, reducing nitrogen rates resulted in much more substantial yield decreases for continuous corn than for rotated corn. For example, rotated corn with no applied nitrogen yielded more than continuous corn with 50 percent of the normal nitrogen rate applied. In addition, reducing rates caused nitrogen stress sooner and with more yield impairment for continuous versus rotated corn.

Similar results have been observed by several university researchers and generally can be attributed to the higher residue levels for continuous corn, leading to Pioneer's recommendation that growers pay key attention to crop residue and fertilizer rates.

To provide further assistance to growers in the future, Pioneer is starting to look into the response of specific hybrids to nitrogen rates and crop rotations. This will be part of the ongoing study as researchers evaluate nitrogen use efficiency among different corn genetics.

"There is a lot of value in analyzing corn responses to crop rotation and reduced nitrogen environments," Shanahan says. "Our goal is to help growers make the best decisions, from hybrid selection to crop management, for their fields."  FG

—Pioneer news release