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College of Food, Agricultural, and Environmental Sciences


Continuous Corn Could Impact Water Quality

June 14, 2007

WOOSTER, Ohio -- With continuous corn production comes increased nitrogen inputs and higher chances of water quality issues associated with run-off. But the concerns lie more with moving land from conservation programs into row-crop production than switching from a multiple crop to a monoculture system, says an Ohio State University Extension nutrient management and soil fertility specialist.

"When you switch to a continuous corn system, you will be applying more nitrogen and applying it more frequently. So the suspicion is that there will be a greater amount of nitrogen discharging into surface waters," said Robert Mullen, who also holds a research appointment with the Ohio Agricultural Research and Development Center. "But when you look at the data that has been collected, the actual amount of nitrogen discharged is not going to be that much different from a multiple-crop system."

Data collected from the University of Minnesota shows that the total amount of nitrate-nitrogen lost through a tile drainage system is similar for a corn/soybean rotation and a continuous corn system.

"This is especially true when corn is sidedressed," said Mullen. "One difference is with early spring applied nitrogen, which does represent a greater risk of nitrate-nitrogen loss."

Where the shift will be dramatic is in pastureland or land that has been pulled out of conservation programs, such as CRP (Conservation Reserve Program), said Mullen. The reason is a function of the change in water dynamics in the soil profile.

"In a row-crop system, nitrate discharges primarily occur in the fall and spring. In CRP land or a permanently vegetative system, like pastureland, we don't get that flush of water in the fall and there is typically less nitrate-nitrogen available for loss due to the continual presence of plants (and the absence of fertilizer nitrogen). Because plants are actively growing/evapotranspiring and taking up nitrogen, water movement through the profile is decreased, so less total nitrate-nitrogen is moving through the soil profile," said Mullen. "Change that system and you'll see more water moving through the soil profile and more nitrate-nitrogen available to be lost."

Though the water quality concerns are there, the good news is that few farmers across the nation and in Ohio are unlikely to be putting their CRP land into row-crop production.

"As of summer of 2006, the government had 27 million acres of land that was going up for conservation program renewal between 2006 and 2009. By the end of 2006, farmers had re-enrolled 23 million acres," said Matt Roberts, an Ohio State University Extension agricultural economist. "This is a hot topic, but the idea that farmers are pulling land out of CRP for corn production to feed the ethanol industry is just not happening, at least not at this point."

Roberts said that most land in conservation programs, such as CRP, are not the most productive for row-crop production, so not much of an economic incentive exists to pull that land out. Also, farmers enjoy the wildlife habitat value the land provides, as well as the long-term economic stability provided by leasing land to the government.

"The most tempting land to pull out of CRP and into production is acres that act as filters or buffers between agricultural land and waterways, and are the ones that are the most environmentally sensitive," said Roberts. "But how much, if any, of the land will be pulled out remains unclear and it's difficult to forecast how that will play out until we actually see it play out."

Mullen sees the biggest challenge in controlling fertilizer run-off and maintaining water quality with increased tillage practices in the face of continuous corn production, especially on sloped land.

"No-tilling continuous corn is not that attractive from a production standpoint, because of the yield drag. So if you grow continuous corn that just means more tillage," said Mullen. "If you are tilling on sloped land or gently sloped land, you are going to run into issues of soil transport from the field. Now you have issues with phosphorus, as well as nitrogen."

Mullen said that although growing continuous corn is economically attractive in the short term given the current commodity prices, a monoculture system may not be the best practice in the long run.

"From an agronomic standpoint, the primary recommendation is still a rotation system of multiple crops," said Mullen. "But for growers interested in continuous corn production, we continue to promote best management practices (average rate and timing, for example) to ensure nitrogen is applied in a fashion that decreases the potential of environmental impact."

For now, it seems Ohio farmers have taken little interest in dramatically increasing their corn acreage for continuous corn production. Though no official acreage numbers from the U.S. Department of Agriculture have been released for Ohio, anecdotal numbers puts increased corn acreage at about 10 percent.

"That's not as dramatic as we had thought," said Mullen.

He speculates that factors such as increased soybean prices and increased fuel prices are offsetting any significant shift into continuous corn production.


Candace Pollock
Matt Roberts, Robert Mullen