Cover crops, microbial community interactions

LEXINGTON, Ill. — Keeping the massive microbial community in soils happy is vital in crop production and research is underway that focuses on the relationships between cover crop selection and microbes.

“Different cover crops can cultivate their own unique microbial communities. Something like a legume such as clover forms associations with nitrogen-fixing bacteria that will add nitrogen back into the soil,” said Emily Hansen, an Illinois State University student pursuing her master’s in biological sciences.

“Each plant is going to have their own specific interactions.”

Hansen’s research at the University Farm is funded by the U.S. Department of Agriculture’s Sustainable Agriculture, Research and Education program, which awards grant funding to research and education efforts promoting sustainable agriculture practices.

“I wanted to see how the cover crops are changing the microbial community in the soil. The microbial community in the soil is called the unseen majority. In just 1 gram of soil there are over 10 billion bacteria and fungi. They play a super important role in the health of our soils and our plants,” Hansen said.

“The way that plants interact with the microbial community is called plant-soil feedbacks. Most of the time these are positive interactions, so the plants and microbes are in a symbiotic relationship where the plants are providing nutrients to the microbes and microbes in turn are making available these really important plant nutrients. These are things like our fertilizer inputs, nitrogen, potassium and phosphorus.

“But sometimes we can have negative plant-soil feedbacks. So, when we’re planting the same crop year after year, pathogens can start to build up in the soil and can cause what’s sometimes been called soil sickness and have a negative impact on our crops.”

Diverse System

A way combat negative plant-soil feedback is by adding diversity back into the agricultural systems.

“One way to do this is by rotating corn and soy, but another way is by adding cover crops. Instead of having barren farmland in the winter, we’ll have some plants there anchoring the soil in place and feeding the soil microbes. This will sustain the microbial community and adds some of beneficial microbes,” Hansen said.

Two-acre plots of cereal rye, pennycress/CoverCress, and an oats, radish, peas and clover mix are sampled in the research. The cover crop fields are compared to a field without cover crops. Soil samples were collected in the fall and this spring.

“We’ve recently seen that there is some sort of lasting effect from cover crops on the microbial communities.”

—  Emily Hansen, graduate student, Illinois State University

Soil samples were collected to a depth of 20 centimeters, or 7.87 inches, and petitioned into 2-centimeter sections for the first 10 centimeters down through the profile.

“With the samples, we’re looking at what the microbes are doing in the soil, what types of carbon can they use, how well they use them, how quickly are the being metabolized,” Hansen said.

“So far we’re seeing as we go deeper into soil these microbes are less diverse. They’re able to use less carbon sources and this really points to how important the plants are at cultivating this microbial community and forming beneficial interactions.

“We’ve recently seen that there is some sort of lasting effect from cover crops on the microbial communities. They are changing what’s happening in our soil in some way and I’m really excited to get back out there this spring and take some more samples and see a little more specifically what cover crops are doing to the microbial community.”

Soil health indicators increase slightly over time with the use of cover crops, according to field trials led by the Soil Health Partnership, but a closer look indicates changes are happening immediately.

“It may take us a while to get that through the entire homogenized profile when we take soil samples, but it’s happening quickly. Any adoption to these practices is making a positive impact on the soil health,” said Rob Rhykerd, ISU Department of Agriculture soil science professor and project collaborator.

“It’s great to see that these interactions with the microbes are happening so quickly, too. This means that potentially farmers could pick a cover crop based on the desired effect they want in the microbial community,” Hansen said.

Regenerative Ag

Nicholas Heller, ISU assistant crop sciences professor, said utilizing cover crops fits into the principles of regenerative agriculture — keeping a continuous living system on the soil year-round to feed the bacteria and fungi.

“When you make it go completely barren for six months at a time, all of a sudden it’s a desert with no food, no protection for those organisms living in the soil. So, they either have to go dormant or die and then reestablish every year when the cash crops are planted. It’s definitely an advantage for the microbial community to have plant sources there and an advantage to the crops as well,” Heller said.

“We’re building a new sequence of study at ISU in regenerative agriculture to focus on these types of ecosystem views rather than looking at the one crop in isolation, but how does it fit into a larger system and make that system something that you implement in an agronomic sense, as well.”