December 10, 2023

Cover crops improve soil ecosystem

MAGNOLIA, Ill. — Soil health is among the most important foundations for sustaining plants, humans and animals.

Only living things can have “health,” so viewing soil as a living, breathing ecosystem reflects a shift in the way soil is observed and managed.

“We’re really looking at the soil function. Those are things like nutrient cycling, water infiltration and storage, plant protection, preventing erosion and storing carbon within our soils. All of these functions are the things we look at when we talking about soil health,” said Stacy Zuber, Illinois Natural Resources Conservation Service soil health specialist. “So, how we can take advantage of that and use those functions to help us in our systems?”

Zuber was among the speakers at the Nutrient Stewardship Field Day hosted July 6 by the Marshall-Putnam Farm Bureau and partners at a cover crop demonstration site.

There are various tools recommended in the state’s Nutrient Loss Reduction Strategy that focus on preventing phosphorous and nitrogen loss into streams, rivers and eventually the Gulf of Mexico.

“Cover crops, to me are, one of the most useful ways to do that because not only does it help us with that nutrient loss reduction, that we can avoid losing those dollars out of our pocket because we’re keeping the nutrients in our soils, we’re avoiding losing them into the water system and causing problems there, but we can also build our soil health,” Zuber noted.

The soil health principles are maximizing continuous living roots, minimizing disturbance, maximizing biodiversity and maximizing soil cover.

Feeding Biodiversity

Maximizing living roots and biodiversity are designed to help feed the soil biology — the living ecosystem within the soil.

“We need to make sure that we’re feeding those organisms within the soil because they’re driving all of these function and really the ones that are making this process happen. We can feed those organism by having living roots as much of the year as possible and we can do that with cover crops. Cover crops are a great way to have continuous roots and giving them a food source throughout the year,” Zuber said.

“We need that biodiversity, as well, and a corn/soybean rotation is two crops over two years, but that’s all you’re getting. We need more biodiversity in there because we really need to feed those microbes a more diverse amount of food. We need to give them a wide variety because if we don’t they start narrowing and we don’t get nearly as diverse of a microbial community and so it’s not able to do the functions, as well.

“If we have diverse cover crops, each plant is giving off different root exudates which are carbohydrates, amino acids and proteins and different chemicals that they are releasing within the soil. Each of those different types of root exudates attracts a different type of microbe.

“The more diversity we have in our plants within our systems the more diversity we have underground and that means they are better able to do all of those different functions within the soil and those processes are happening at a higher level so we can take advantage of that.”

The healthy soil then has to be protected by minimizing disturbance and maximizing soil cover.

“Even if we build it, if we don’t stick with that, it can degrade and go back to what it was before. We want to focus on protecting what we have there, protecting the soil aggregate, protecting the soil organic matter,” Zuber explained.

Improved Aggregation

An added bonus to increasing organic matter and soil organism, reducing compaction and improving nutrient storage and cycling is improved soil aggregation.

Aggregates are formed by microbial glue that holds mineral particles. Root exudates, fungal hyphae and dead microbial cells are among the systems that create the “glue.”

“When we don’t have good aggregation, we do not have pore spaces. There’s nowhere for oxygen to move through. There’s nowhere for water to move through. It is blocked,” Zuber said.

“We’ve had heavy rainfall events the last couple of weeks. We have more and more of those happening more frequently. In order for our fields to be able to deal with that there needs to be somewhere for that water to go and if it hits a field that does not have good aggregation the rain hits the surface, some of those particles become loose in the water. If there’s a low spot in the field you have ponding. More of that starts settling out, blocking more and more of those pore spaces that might have been there.

“So, whatever pore spaces you might have had, you get less and less of those over time because of continually being blocked as the particles settle into any open spaces there are. If it runs off, now you have erosion. The particles are leaving the soil, they’re taking organic matter with it, they’re taking phosphorous with it and then we have nutrient losses, as well.

“Aggregate stability and aggregation of soils is one of the most important benefits you can get from improving your soil health.”

If a tillage pass is necessary because of some issue in a field that has healthy soil, the diverse microbial community is already in the field, the soil is more resilient and can recover much faster from the disturbance.

“Cover crops really fit into three of the soil health principles. They’re giving us soil cover, continuous living roots and the biodiversity. We also get the additional benefit of nitrogen scavenging,” Zuber said.

“One of the other things to emphasize when we’re talking about nitrogen scavenging for cover crops is a lot of the times with our Nutrient Loss Reduction Strategies we focus on those four ‘Rs’ — right place, right source, right timing, right rate — to reduce fertilizer loss.

“That’s super important. I’m not minimizing that, but we still have a lot of nitrogen losses from our fields that is just coming from mineralization. The best way to keep that in place is by using cover crops so we’re able to minimize our losses from our fertilizer, but we also keep that nitrogen there that would otherwise be loose in solution and be lost because we don’t have a crop out there, we don’t have a plant to take it up.

“That’s where cover crops really fit the bill for us to do so many of these different things at the same time and give us additional benefits for our soil health, helping us to have more productive soils.”

Tom Doran

Tom C. Doran

Field Editor