Reducing nitrogen runoff: Cover crops help solve problem

CHICAGO — One way to control runoff of nitrogen and phosphorus is to have a growing crop on the field.

“That’s why cover crops are so important,” said Gary Schnitkey, professor at the University of Illinois and U of I Extension farm management specialist.

“If we can reduce nitrogen moving from farm fields into water and down to the Gulf, we will also reduce the hypoxia,” Schnitkey said during the Improving Midwest Agriculture and the Environment meeting. “That is where a lot of emphasis is at right now in Illinois.”

Nitrogen needs to be in the organic form to make it available for corn plants to use, said Schnitkey at the annual Agriculture Conference at the Federal Reserve Bank of Chicago.

“There are two ways we get nitrates, by putting fertilizer down or the soil converts organic nitrogen into inorganic nitrogen which is a process that happens every year,” he said.

If farmers did not add any synthetic fertilizer to fields, there still would be nitrates produced and probably runoff, Schnitkey said.

“Nitrate leaching concerns are the largest in the spring because organic nitrogen has converted to inorganic nitrogen and we’ve put on synthetic fertilizers,” he said.

In addition to cover crops, nutrient runoff also can be impacted by edge-of-field technologies, tillage practices and the timing, rate and form of nitrogen application.

To evaluate some of the economics of these practices, the Illinois Corn Growers Association initiated the Precision Conservation Management project.

“People contributing to this program are farmers and it looks at tillage, cover crops and nitrogen management,” Schnitkey said.

For cornfields, the PCM project evaluated several types of tillage, including no-till, strip till, one-pass, two-pass and two-plus pass.

“For yields from 2016 to 2018, the no-till produced 212 bushels per acre, which was the lowest yield, but it also has a lower cost,” Schnitkey said.

“We’d like to see people move to strip till because it has the advantage of tillage, you’re still getting the environmental benefits and it’s one of the highest for operator and land return.”

The tillage results for soybeans from 2016 to 2018, showed that even though the no-till had lower cost, the one-pass system had higher returns than no-till.

“We see no advantage to going to a two-plus pass system,” Schnitkey said.

Farmers in the Corn Belt have several opportunities to apply nitrogen, including in the fall as anhydrous ammonia.

“You can cover acres fast and it can also be part of a strip-till system, but you have increased chance of nitrogen effluent,” Schnitkey said. “It is the lowest cost of applying nitrogen, but you should use an nitrogen inhibitor.”

Anhydrous ammonia also is applied in the spring before planting.

“You may or may not get it on and 2019 was a prime example,” Schnitkey said. “And once you put nitrogen on in the spring, you need to wait a week before you plant.”

Applying UAN post plant early increases the cost, Schnitkey said.

“It does reduce the chance of nitrogen effluent because you’re putting it on at the time of planting,” he said. “If you’re putting nitrogen on after planting, almost always you have to put some nitrogen on before planting because you want nitrogen there when the plant first starts growing.”

A late application of nitrogen on standing corn is expensive, Schnitkey said, and there is a very short working window to get the job completed.

“Farmers in Illinois put most of the nitrogen on in the fall, but also put something else on such as DAP or UAN mostly as pre-plant,” he said. “The fall application is not as low cost as you expect because the nitrogen inhibitor adds cost.”

When selecting a cover crop, Schnitkey said, it is a good idea to pick one that overwinters so it will be growing in the spring to trap the nitrates.

“Our PCM data shows about 10% of the fields were planted with over-winter cover crops and the soybeans had a little higher yield but roughly the same returns,” Schnitkey said.

“We’re seeing a movement towards practices that lower nitrogen losses,” he said. “The lowering of rates may be the most promising and there is also a movement towards split or reduced applications.”

There are known environmental benefits for cover crops, Schnitkey said.

“Cover crops reduce nitrogen moving to water bodies but the economic benefits are less well known,” he said.