“Our research shows that corn residue acts like a ‘sponge’ immobilizing the fertilizer, making it temporarily unavailable to the corn plant,” said John Shanahan, Pioneer agronomy research manager. “Growers working with continuous corn need to be mindful of crop residue from the previous year and adjust (and likely increase) their nitrogen fertilizer rates accordingly.”
These findings are part of a long-term, multi-location study by Pioneer that began in 2006 to examine the response of corn in limited nitrogen environments. Evaluations have been conducted yearly at Pioneer research stations in Johnston, Iowa; Champaign, Ill.; Windfall, Ind.; and York, Neb.
“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%), 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 said. “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% 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% 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 said. “Our goal is to help growers make the best decisions, from hybrid selection to crop management, for their fields.”