Worms, fungal glue, chemicals leaking from plants and the droppings of tiny mites: this unappetizing cornucopia is just one sample of the rich world of soil, where subterranean microbial communities are key to agricultural productivity.
“When you stand on your own land, you stand on the roof of another world that serves you,” says Jill Clapperton, a private soil health researcher and speaker.
Speaking via Zoom on Jan. 23 at the Pennsylvania No-Till Alliance meeting at the Lancaster Farm and Home Center, Clapperton offered some ideas for building healthy soil.
1. Build the soil, starting with the root zone
The root zone or rhizosphere is the most biologically active part of the soil. After all, the roots of living plants anchor the entire soil ecosystem, Clapperton said.
Mycorrhizal fungi colonize around the roots, exchanging nutrients with the plant. In this process, the fungus acts as a barrier against pathogens. They also produce a gel-like substance called glomalin that stabilizes the soil and helps it resist erosion.
Mycorrhizal fungi grow around the roots of most plants, including corn, soybeans, and even weeds like Johnson grass. But they are not associated with brassicas such as rapeseed.
Despite their importance, these fungi are only a small part of the soil ecosystem, Clapperton said.
Most soil microbes are decomposers, while others are predators that move nutrients through the system.
Small mites eat fungi. Mites concentrate nutrients in their feces, which contributes to soil structure and provides food for bacteria and other fungi. Add to that protozoa, nematodes, and insects, and there’s a whole host of things that eat other organisms or their excretions.
Clapperton said some of the microbes that would otherwise be eaten in this food web might try to attack the plant.
At the heart of this system are fungi that secrete enzymes that allow them to break down woody crop residues and obtain nutrients from them.
“We need them to do that because they take all the good stuff and start recycling it,” Clapperton said.
For her, the first step in maintaining these healthy underground communities is letting plants grow in the soil and minimizing soil disturbance through practices like no-till.
“Soil is a habitat, and you can’t keep destroying habitat and expect that you’ll actually succeed” in building soil, Clapperton said.
2. Adding plant species to fields can bring benefits
Planting a variety of species in a field—whether a cover crop mix or cash crops paired with companion crops—provides the soil with plants that support different microbial communities.
The study also found that growing multiple species together absorbs less soil moisture than a single crop.
Abundant plants in multi-species fields shade the soil well. This cools the ground and allows roots to function on hot days where, with a monoculture, they might stop growing.
In addition, multi-variety planting has the skill of sharing water and nutrients.
“They’re all intertwined,” Clapperton said. “They share resources. Those that get more because of mycorrhizae, they share with those that don’t get as much.”
3. Choose the right cover crop for your purpose
Plant diversity is only good when all species are sprouting, so a package containing a dozen species may or may not be what a farm needs. Clapperton recommends farmers try growing a mix of three species.
Sometimes, cover crops may not be suitable for a field. In dry Kansas, Clapperton noticed that her Milo suffered every time it rained—the opposite of what it was supposed to do.
Rye cover crop residue persisted in dry conditions, and Clapperton determined that rain was washing allelopathic chemicals that inhibit competing plants away from the rye residue and into Milo.
The mid-Atlantic has a wetter climate than Kansas, so this scenario is less likely in Pennsylvania, but not impossible.
“I would say more diversity, more broadleaf trees, not so much rye, so that doesn’t happen to you anyway,” Clapperton said.
Perhaps more importantly, Clapperton recommends planting your biggest and best cover crops before corn and soybeans, rather than small grains.
The root systems of wheat and similar plants are too small to support rich microbial communities, so hungry ecosystems could collapse, she said.
4. Trace elements help plants protect themselves
When insects start feeding on a plant, the plant sends signals to its neighbors to protect itself.
These plants accumulate lignin and other substances that insects dislike in their leaves, a process that requires trace elements.
“Our job is to make sure those micronutrients are present and available to them so that if they have to put on the armor, they can do it,” Clapperton said.
In fact, fungicides contain trace minerals that help deliver the active ingredients, and Clapperton believes these micronutrients do more than farmers realize.
“I believe that sometimes when we see advantages from fungicides, it’s not from changes in disease patterns but from the nutrients provided by the fungicides themselves,” she said.
In some cases, farmers might try using humic acid instead of fungicides and adjusting foliar fertilizers to a neutral pH, she said.
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