Cover crop trials include N, P efficiency

LEXINGTON, Ill. — Illinois State University and Western Illinois University have teamed up in a joint cover crop project funded by the Illinois Nutrient Research and Education Council.

The project will assess diverse cover crops for nitrogen and phosphorous efficiency, carbon sequestration, and the economic impacts on Illinois crop rotations, and is an expansion of the ongoing research that was previously underway.

“One of the things we haven’t been able to do with these plots was to look at the nutrients, in particular nitrogen and phosphorus,” Rob Rhykerd, ISU soil science and agronomy professor, said at a recent cover crop field day at the ISU Farm.

With this in mind, Rhykerd and a group presented a proposal for funding to Illinois NREC.

“We received funding, so we’re going to continue with these plots but also look at what’s going on with nitrogen and phosphorous,” Rhykerd said.

“Bill Perry (ISU water ecology professor) will install lysimeters. So, we’ll be able to pull out soil core water and analyze that for total nitrogen, ammonium nitrate and phosphorus, and we’ll look at that in the soil sample, as well.”

Win Phippen, WIU plant breeding and genetics professor, and Tad Wesley, WIU research agronomist, are replicating the experiment at the WIU Farm.

“One of the things that would be interesting is sequestration with pennycress and then perhaps some other cover crops as well,” Rhykerd said.

Early Findings

Ongoing trials began in 2020 focusing on implementing cover crops in a corn-soybean rotation.

Cover crops used in the trials include pennycress; cereal rye; and a pea, clover, radish and oat mix.

“The pea, clover, radish, oats is an interesting cover crop mix. Theoretically, you’ve got the radishes and oats coming up in the fall and give you some cover and then they die out over the winter and then the peas and clover come in in the spring and those are legumes that provide the nitrogen fixation benefits for the next summer cash crop,” Rhykerd noted.

As expected, the oats and radishes came up in the first fall of the trial.

“They looked good, they had ecosystems services and helping pull some nutrients out of the soil and helping with erosion issues. They died out and in the spring the clover looked beautiful and there were some peas mixed in and it was a really wonderful looking crop,” he said of the trial’s first year.

“In year two, I don’t know what happened. We planted it and really nothing much came up in the fall and then in the spring all the radishes came up which was a surprise to me, but they looked great.

“One of the cool things about that mix is just the diversity. So, when you have some differing weather patterns, it maybe selects one of those crops over the others but you still have a lot of biomass produced and a great ecosystems services as far as good coverage out there. So, that’s been a really interesting one to watch.

“This year, the peas came up in the fall. So, we had three years, three completely different results. That’s why it’s interesting to study these things long term and look at the different results.”

Soil Tests

A more detailed approach to soil sampling was introduced into the research for a more specific read on organic matter.

“When you pull a traditional soil sample, you go down 6 or 8 inches and you homogenize that up and send it off to a lab,” Rhykerd explained.

“But one of the knocks with cover crops is it takes several years to notice any changes in the soil properties. So, we decided to take that soil core down into 2-centimeter increments through the top 10 centimeters, then we did 10 to 15, 15 to 20 centimeters, and so on, so we could pick up any of those differences from the surface and what is the immediate increase in organic matter.

“We pulled soil cores in both the fall and the spring and we’re finding pretty significant increases in soil organic matter on all of the cover crop treatments in the spring and some of that still carries over into the fall, especially in the top 2 centimeters.

“Cereal rye, as you would expect, produces the most biomass. So, we’re seeing the greatest amount of organic matter increase in the top 2 centimeters. But the pennycress is significantly increasing the organic matter content as well.

“We really haven’t seen that move down much in the subsoil yet. It will be interesting as we continue this to see how quickly and when that organic matter begins to move its way down into the soil.”

Crop Yields

The trials also are focusing on the impact of cover crops on the corn and soybean yields.

Soybeans were grown after cover crops in 2021 and corn followed in the 2022 program.

“For yields, the soybeans that first year that followed pennycress yielded no significant difference than the soybeans without cover crops. That was really encouraging,” he said.

“We did see a slight decrease in yield from cereal rye this past year. The corn for the trial was planted June 1 and it ran into the summer drought issue. All the cover crops did drag the corn yield down, but pennycress had one of the least yield drags. It didn’t pull quite as much moisture out of the soil in the spring, but compared to the control plots, yields were down a little bit.”