The Tiny Critters Beneath Our Feet Keep Us Healthy
Diana Wall has spent so much time studying soil in Antarctica that there’s a region, Wall Valley, named after her. The soil ecologist and professor at Colorado State University has gotten to know soil pretty well, yet she continues to learn about ways in which healthy soil is important not just for good agriculture but for entire ecosystems and, increasingly, for human health.
Last November, a few weeks before departing for her latest research trip, Wall published a paper highlighting examples of the link between soil health and human health. Strongyloides, for instance, are parasites that can penetrate human skin and reproduce in the intestine. Researchers found higher rates of infection in areas of Cambodia where there was a loss of organic carbon in soils that had been converted from forest to agriculture. It’s unclear what drives infection rates, but the connection suggests that increasing organic carbon levels in cropland—also a tactic for combating climate change—could be effective in reducing disease-causing parasitic worms.
“Soil biodiversity is really important for food production, healthy animals, healthy lives, because there are organisms in the soil that control the other organisms,” Wall said in a phone interview from Antarctica. “It's just like predators aboveground. You have predators at the top of the food chain—sharks in oceans that control the populations of other animals. When we disturb soil, we lose those predators, those controls on some of the invertebrates that can become parasites and pests of humans and wildlife.”
For example, a root weevil that damages Florida citrus plants is sometimes controlled by roundworms that kill the pest. Many antibiotics originated in soil, and future drugs are likely to as well. Research has also shown that exposure to soil microbes can reduce allergies.
Working in Antarctica has allowed Wall, who is researching the impact of climate change on soil, to study the underground food web in as close to a controlled laboratory environment as possible because there is little life above the soil.
The World Wildlife Fund estimates that half of the world’s topsoil has been lost. Last month, the United Nations Food and Agriculture Organization released a report assessing soil health in eight regions around the world. Researchers found that more frequent agricultural harvesting—even though it allows for higher crop yields—has decreased soil quality and increased the risk of pathogen diseases. The dirty truth: Where soil quality and biodiversity have been diminished, so too has human health.
In Australia, a bacteria that normally exists at low levels was able to proliferate in soil that was not well drained after heavy rain. It then triggered a sometimes fatal disease, melioidiosis, in birds and people.
“Soil that is properly drained and aerated regulates the prevalence of this bacteria and keeps it in check,” the study’s authors wrote. “Soils rich in biodiversity produce healthier and more nutritious foods and control the proliferation of any pathogenic microorganisms that affect both plant and human health.”
Wall said one challenge is to persuade farmers and others who work the land to put soil science to everyday use.
Patrick O’Neill, an agronomist in Alamosa, Colorado, said the San Luis Valley Soil Health Network was established in 2010 to do that. Many farmers in the network joined while searching for ways to cope with drought. Some had started to leave portions of their land fallow to save water. But when they planted the following year on that land, crops didn’t grow as well. “There needs to be some investment, even in the off-year when you don't have a cash crop to sell off that farm, to feed the soil, to feed the microbes in the soil and keep that system alive,” said O’Neill.
Approximately 275 farmers belong to the network, and O’Neill guesses that a good many of them have tried to adopt at least some of the practices promoted by the group. Among them: reducing pesticide use or switching to low- or no-till farming—growing crops without disturbing the soil by plowing every year, a practice that’s increasingly understood to be more ecologically beneficial.
Similar partnerships are sprouting up around the country. Iowa, for example, has set up a network of demonstration farms that growers can visit to observe practices that benefit soil, such as reduced tillage and the use of cover crops. The goal is to measure the benefits of such practices and promote their use on other farms around the state. An initiative announced in December, the Soil Health Institute, aims to bring together farmers, researchers, and policy makers at a national level.
“I think people are starting to understand that properly managing soils is going to be key for global food supplies,” Wall said. “If we properly manage these organisms, we not only help soil health, but we help human health.”