You’ve heard the good, bad and ugly about cover crops. Hoosiers continue to plant more than a million acres each year. Obviously, many people see the good that cover crops can accomplish. Shalamar Armstrong’s mission is to help more people understand how to manage cover crops to avoid bad or ugly situations.

Armstrong is a Purdue University Extension agronomist. He’s excited about the potential for cover crops. But he acknowledges that before some people invest in cover crops, they need to understand how cover crops affect nitrogen cycles in the soil, as well as see proof that cover crops can play a positive role in supplying more nitrogen to crops for better yields.

“We were involved in a three-year on-farm trial in Illinois before coming to Indiana,” Armstrong says. “Fall nitrogen application is still prominent in some parts of Illinois. We wanted to see if cover crops could help reduce nitrogen losses in tile lines, especially in fall nitrogen application systems.

“Once nitrogen leaves the field in tile lines, it can wind up eventually in the Gulf of Mexico and contribute to hypoxia. That’s basically a condition where there isn’t enough oxygen for fish and other marine life to exist. If nitrogen leaves the field, the grower is also losing out on valuable nutrients.”

Understand trial results
Results of the three-year trial make the case for studying all the information known about a test before drawing conclusions. Armstrong says cover crops helped reduce loss of nitrogen through tile lines for both fall- and spring-applied nitrogen. There was a sizable reduction in the amount of nitrogen lost when cover crops were added to the system in both cases, he observes.  

Here’s where the results get tricky. He saw yield reductions in some years where cover crops were used. “You have to know that it was cereal rye ahead of corn,” he says. “On that particular farm the grower wasn’t adding nitrogen as starter at planting time.

“Cereal rye, especially if it grows tall in the spring before termination, ties up a lot of nitrogen,” Armstrong explains. “It’s good that it’s tied up and not lost through tile lines into rivers and streams. However, once it’s tied up, it’s not readily available to young corn plants soon after the cover crop is killed. There is a lag between when the cover crop is terminated and when it begins to release nitrogen back to the soil that could be used by the crop. Unless you add supplemental nitrogen for young corn, the crop can actually run short of N in the early stages because so much of it is tied up.”

Many no-tillers in Indiana, like Mike Starkey, Brownsburg, have learned to apply nitrogen when no-tilling into cover crops to give corn what it needs until nitrogen is released.

The other option is to not use cereal rye ahead of corn, Armstrong says. Starkey typically uses a five-way mix of cover crops ahead of corn, including annual ryegrass and crimson clover, but not cereal rye. Cereal rye works well ahead of soybeans, Starkey says.