Soil: a climate change hero?
The world is getting hot, but what does soil have to do with it? Quite a lot, in fact! In the years to come, one of the most important jobs of soil will be to help us recapture the very thing making our world too warm, carbon.
Carbon is a tiny molecule, and one of the most important building blocks of life. It provides a sort of “backbone” for many of the materials that make up the environment around us, and even our own bodies. Without carbon there would be no trees, no grass, no humans, and not much else. How can carbon, so necessary for life, be causing a disaster as big as global warming?
When carbon is stored in safe places like the soil as dead plant matter, or deep in the ground as coal or oil, carbon can’t trap heat in our air. Carbon becomes a problem only after it is transformed into a gas, carbon dioxide, or CO2. Once in the air, CO2 molecules absorb energy given off by the sun, trapping this energy near the earth’s surface. You and I perceive this newly trapped energy as heat.
We often hear about CO2 being released through burning gasoline in cars or coal in power plants. An underappreciated amount of CO2 in our air has been released from soil. In fact, most agricultural soils now store less than half of the carbon that native prairies did before we started farming.
How does farming release CO2 into the atmosphere? In a word, tillage. Tilling the soil exposes dead plants to bacteria, which rapidly decompose dead vegetation. Carbon, held within dead plant tissues, is released by bacteria into the air as CO2. Frequent tillage during each growing season results in much less carbon being captured by plants and “pumped” back into the soil. Under this scenario there is much more carbon being lost than captured.
Less carbon in the soil harms farmers and rural communities in two important ways. First, more CO2 in the atmosphere will result in a warmer earth causing severe disasters such as global food shortages and dangerous weather extremes. Second, less carbon in the soil makes for poor crop growing conditions.
Soils with less carbon require considerably more fertilizer to grow healthy crops. Part of the reason why more fertilizer is applied to cropland now than at any other point in history is because soils have less carbon to hold onto nutrients. Loss of these nutrients is bad news for the farmers who pay for this costly input, but also dangerous for humans and other animals which can be harmed by drinking water possessing excess agricultural and residential fertilizer.
There is good news, however. New farming practices which result in more carbon being stored in soils do exist and they are gaining in popularity. Planting into the standing residue of previous crops would have once been a crazy idea, but thanks to improved farming equipment and research, this practice is commonly done without having to till cropland, saving farmers both time and money. Cover crop use is also on the rise. These non-crop plants allow a farmer to expand the period of plant growth during a growing season to capture as much carbon in their soils as possible.
Benefits of increasing soil carbon get larger as more carbon is stored over time. In fact, a recent study conducted across several Midwestern farms found a positive correlation between the amount of carbon held within a farm’s soil and overall farm profit. It turns out that what is good for our climate is also good for a farmer’s wallet.
We are living through exciting times in the world of agriculture. Cropland managers are adopting new technologies and farming decisions are more commonly based on improving soil function. These key changes will have positive impacts on local farming economies and natural resources but will also influence the much larger issue of our changing climate.
