Worms, fungal glue, chemicals leaked from plants and the feces of microscopic mites: This unappetizing cornucopia is just a sampling of the teeming world of the soil, where underground communities of tiny organisms are key to farm productivity.
“When you’re standing on your ground, you’re standing on the rooftop of this whole other world that is there to work for you,” said Jill Clapperton, a private soil health researcher and speaker.
Speaking via Zoom, Clapperton offered some ideas for building healthy soil during a Pennsylvania No-Till Alliance meeting Jan. 23 at the Lancaster Farm and Home Center.
1. To Build Soil, Start 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 roots to exchange nutrients with the plants. In doing so, the fungi serve as a barrier against pathogens. They also produce a gluelike 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 johnsongrass. But they don’t associate with brassicas like canola.
As important as these fungi are, they are only a small part of the soil ecosystem, Clapperton said.
Most soil microbes are decomposers, and others are predators that keep nutrients moving through the system.
Tiny mites eat fungi. The mites concentrate nutrients in their scat, which contributes to soil structure and provides food for bacteria and other fungi. Add in protozoa, nematodes and insects, and there’s a lot of things eating other organisms or their waste.
Some of the microbes that get eaten in this food web would otherwise be trying to attack the plant, Clapperton said.
Central to this system are the fungi that exude enzymes allowing them to break down woody crop residue and mine it for nutrients.
“We need them to do that because they take all the goodies out, and then they start recycling them,” Clapperton said.
To her, the first steps to maintaining these healthy underground communities are to keep plants growing in the soil, and to minimize soil disturbance through practices such as no-till.
“Soil is a habitat, and you can’t go destroying the habitat all the time and expect that you’re actually going to succeed” in building the soil, Clapperton said.
2. Adding Plant Species to a Field Can Have Benefits
Planting multiple species in a field — whether in a cover crop mix or a cash crop-companion crop pairing — provides the soil with plants that support different microbial communities.
Research has also found that multiple species growing together can draw down soil moisture less than a monocrop will.
The abundance of plants in a multispecies field shades the soil well. This cools the ground and allows roots to function during hot days when they might shut down in a monocrop situation.
Moreover, multispecies plantings also have a knack for sharing water and nutrients.
“They’re woven together,” Clapperton said. “They share resources. Ones that get more because they’re mycorrhizal, they’ll share with ones that don’t get as much.”
3. Select the Right Cover Crop for Your Purposes
Plant diversity is only good if all of the species germinate, so packages with a dozen species may or may not be what a farm needs. Clapperton recommends farmers try growing mixes with three species.
Occasionally, a cover crop may prove unsuitable for a field. In dry Kansas, Clapperton noticed her milo suffered every time it got rain — the opposite of what it was supposed to do.
The rye cover crop residue had persisted in the parched conditions, and Clapperton determined the rain was washing allelopathic chemicals, which inhibit competitor plants, out of the rye residue and into the milo.
The Mid-Atlantic climate is wetter than Kansas’, making such a situation less likely in Pennsylvania — but not impossible.
“What I would say is more diversity, more broadleaves, not as much rye, and then that way that can’t happen to you no matter what,” Clapperton said.
Perhaps more important, Clapperton recommended planting the biggest and best cover crops before corn and soybeans, not small grains.
Wheat and similar plants have root systems that are too small to feed an abundant microbial community, so the starved ecosystem may tank, she said.
4. Trace Elements Help Plants Defend Themselves
When insects start feeding on a plant, the plant sends a signal to its neighbors to protect themselves.
In their leaves, the plants build up lignin and other substances unpalatable to insects, a process that requires trace elements.
“It’s really our job to make sure that those micronutrients are there and available to them so that if they have to armor up, they can,” Clapperton said.
As it happens, fungicides are loaded with trace minerals that help with the delivery of the active ingredient, and Clapperton thinks these micronutrients are doing more than farmers realize.
“I’m convinced that sometimes when we see advantages of a fungicide, it’s not from a change in the disease pattern, but actually from the nutrition that’s being provided by the fungicide itself,” she said.
In lieu of a fungicide, she said farmers might in some cases try applying humic acid with a foliar fertilizer adjusted to a neutral pH.