What many thinks of as “just dirt” is an incredibly complex mixture of rock-derived minerals, plant-derived organic matter, dissolved nutrients, gases, and a rich food web of interacting organisms.
By ploughing and overtilling, we have increased erosion on agricultural fields by 10 to 100 times natural rates. Over just the last several decades, we may have lost about half of the topsoil that natural processes produced over thousands of years in the U.S. corn belt.
Topsoil is rich in soil organic matter – dark spongy material formed from decomposed plant and animal tissue. Soil organic matter is critically important: It helps soils hold onto water and nutrients and supports soil microbes that recycle nutrients. Loss of soil organic matter has made many farms increasingly reliant on fertilizers, pesticides, and herbicides.
Much recent research has focused on adding organic material back to soils to restore them. This is an important strategy, but I believe we also should aim to enhance the microbes that are responsible for soil formation. I was part of a research team that demonstrated in a 2015 study that adding efficient microbes to soils can enhance the percentage of plant carbon that is transformed into soil. New research suggests that by fostering an efficient and active soil microbiome, we can accelerate soil regeneration far beyond typical rates seen in nature.
It takes a village to make healthy soil
Natural soils are thriving with life. They contain an incredible diversity of microscopic bacteria, fungi, viruses, and other organisms. A single handful of soil can contain tens of thousands of different species.
These microbes interact closely with each other, forming complex networks. They communicate with chemical signals. They work together to break down complex organic materials, including dead plants and animals. They often work in teams to complete biochemical processes, such as transforming nitrogen from an inert gas to plant-usable forms and recycling it from dead plant materials back into dissolved forms.
In healthy soils, organic matter is protected from decomposition inside clumps of soil called aggregates. But tilling crushes aggregates, unlocking their carbon and allowing microbes and soil fauna to attack it.
This creates a temporary feast for soil microbes, but eventually they deplete their food supply and die off. Without a healthy microbial community, nutrients are no longer recycled, opportunistic pests can invade, and farmers rely increasingly on chemicals to replace biological soil functions.
Reviving agricultural soils
Soil degradation is a critical problem because it threatens our ability to produce enough healthy food for a growing human population and contributes to climate change. In response, large companies, non-profits, scientists, and government agencies are working together to restore soil health.
For example, General Mills is working with the Nature Conservancy and the Soil Health Institute to encourage farming practices that begin to rebuild soils.
The first step to improving soil health is to stop the bleeding. Instead of leaving fields barren in between crops, which leads to erosion, farmers are increasingly planting cover crops such as rye grass, oats and alfalfa. They also are replacing intensive tilling with no-till practices to prevent the breakdown of soil structure.
Soil organic matter contains over 50 percent carbon. Globally, soils contain more carbon than plants and the atmosphere combined. Losing carbon-rich organic matter from soils releases carbon dioxide, a greenhouse gas, which can accelerate climate warming. But by regenerating our soils, we can sequester more carbon underground and slow climate warming.
In addition to protecting soil, cover crops take carbon out of the atmosphere as they grow and funnel it into the soil. Unlike cash crops that are harvested and removed from the soil, cover crops are left to decompose and contribute to soil formation.
