U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) research microbiologist Michael Lehman takes a soil-core sample on David Gillen’s South Dakota farm. Among other things, such samples can be tested for the diversity and activity of soil bacteria, fungi, algae and other microorganisms. (Photos courtesy of USDA-ARS.)
Space may be the final frontier, but soil biology is the next frontier. Researchers are only beginning to understand the richness, diversity and complexity of the bacteria, fungi, algae and other microbes thriving in the ground underfoot, and just how critical soil health is when it comes to keeping the Earth’s overall ecosystem intact.
“Without microbes, life doesn’t work,” said U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) research microbiologist Michael Lehman, who collaborated with 14 other soil experts on a major, overarching article in 2015 that described the yawning chasm between what we know about soil microbiology and what we need to know.
A large part of that gap results from an inability to examine the microbial world in soil.
“In well-studied systems, scientists have been able to ask questions and get answers, and that’s why those systems are well-studied,” said Lehman, who is stationed at the North Central Agricultural Research Laboratory in Brookings, South Dakota. “For instance, if you wanted to look at trees in a certain forest, you could go out there, actually count every individual tree, and probably identify every single individual tree to species. We can’t possibly do that with the organisms in the soil.”
New technological tools, however, are beginning to shed some light on soil microbes. These include such technologies as the burgeoning DNA and RNA sequencing capabilities, stable isotope probing and various gene-expression techniques that can assist in identifying these microbes and the roles they play, Lehman said.
“With these technological advances, we’ve already discovered so much more than we ever thought in terms of diversity and numbers alone, and with the incredible complexity of this system, it’s become clear that we are really primitive in our fundamental knowledge of the physiology and ecology of nearly all these organisms,” he said.
As an example of the lack of understanding about soil biology, Lehman pointed to nitrogen-fixing bacteria.
“For 50 to 60 years, soil microbiologists have measured the activity of two or three organisms and their potential to convert nitrogen from ammonia to nitrate. But in the last five years, it’s been found that totally unrelated microorganisms actually might be doing most of that nitrogen conversion in soils,” he said. “These are microorganisms that had never been known before, (and they include) nitrogen-fixing bacteria that don’t fit into the conventional nodulating-rhizobial model, but are just living in the roots, fixing nitrogen and giving it to plants.”
Additional new research indicates that other microbes can help make phosphorus, potassium and various trace nutrients more available to plants, and if those microbes are encouraged, the need for fertilizer could potentially be reduced.
“So we’re learning that there are all kinds of ways that the microbes support plants,” he said.
Two U.S. efforts are under way to chip away at the vast mystery of soil biology. One is the National Corn Growers Association’s Soil Health Partnership (soilhealthpartnership.org), which is studying soil-management practices at 60 demonstration farms, 20 of which will be added in 2016.
The other is a national soil-health assessment to be spearheaded by the newly launched Soil Health Institute (soilhealthinstitute.org) based in Research Triangle Park, North Carolina. Similar studies of soil health are underway in the European Union, Brazil, Argentina and Australia.
Said Lehman, “Soil biology has become a global interest, and I think studies like these will yield important advancements about how farm practices can positively influence soil health.”
Lehman and his co-authors wrote their paper to stimulate interest and awareness of soil biology to everyone from scientists and crop producers to policy makers and nonprofit organizations, he said.
“We wanted to reach a lot of different audiences to illustrate how little we know about soil health, how far we need to go, and what we need to do to get to that endpoint,” he said. “We also wanted to try to spur additional efforts, whether they are government or nonprofit initiatives that are coordinated across regions, or individual investigator-led projects.”
The main point, he added, is that soil biology is too important to ignore. “If it weren’t for the microbes in the soil, life wouldn’t exist. Period.” •
– by Leslie Mertz
ONLINE Lehman, R. M., et al. “Understanding and Enhancing Soil Biological Health: The Solution for Reversing Soil Degradation,” Sustainability 2015, available at bit.ly/1VehlCH
Tips to improve your soil
Although the study of soil microbiology is barely out of the starting gate, U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) research microbiologist Michael Lehman said growers can already take steps to reduce and even reverse soil degradation:
—Disturb the soil as minimally as possible. One of the main consequences of disturbance is the destruction of the soil structure, which disrupts soil habitats for valuable microbes and removes organic carbon from the soil faster than it is naturally replenished.
—Keep something growing on the soil all year round. “This is kind of a big deal, because plants will take about 25 percent of what they fix as carbon from their photosynthesis and inject it into the soil,” Lehman said. “By doing that, they’re providing an organic source for the organisms that live near the plant and therefore maintain the biomass of microbes, their activities and also their diversity.”
—Maintain diversity where possible. For fruit growers, this could mean growing a diversity of plants as cover crop between tree rows or in adjacent plots. Research has linked the diversity of plants to increased nitrogen and carbon retention provided by soil microbes. A mix of perennials could be a good option, because they have deep roots that stabilize soil, access nutrients and water from deeper in the profile, and stimulate microbes through a greater cross-section of soil, he said.
—Avoid heavy inorganic-fertilizer use. “There’s plenty of literature out there and more research still coming out, that suggests that if you add high levels of inorganic phosphorus and nitrogen, you can suppress certain populations of microbes that would otherwise be beneficial to the plants,” Lehman said. He acknowledged that firm guidelines are not yet available for fertilizer use, and may not be forthcoming anytime soon. “Today’s fertility recommendations were made under a standard set of conditions that did not optimize soil biology,” he said, adding that the recommendations are for “average” conditions so they may not apply well to every orchard or vineyard. “To translate the new understanding of soil biology into recommendations is going to take a long time.”
—Use compost and manure. Organic compost and manure trump inorganic fertilizers, he said. “They increase the health of soil by adding carbon in the organic form that stimulates biological activity in a way that inorganic doesn’t. With inorganics, you’re putting out a pool for plants to uptake. With organic forms, you’re stimulating the biological cycle so it can provide the nutrients to the plant.”