August 21, 2015

Monoculture—planting fields of just one crop, like corn—may be squeezing out grassland and wildlife in rural America. But according to journalist Kristin Ohlson, it could also be contributing to climate change. Ohlson is the author of The Soil Will Save Us: How Scientists, Farmers, and Foodies Are Healing the Soil to Save the Planet. She says up to 80 percent of the carbon in the world’s soils has been lost. But changing our farming practices could help reverse that—and potentially, reverse climate change too. Recently, Kara Holsopple talked with Ohlson about her book. Here are some of the highlights from the interview.

On how soil stores carbon

"The thing that we all have to understand is that soil is very much alive, and it’s alive with microorganisms that have been there for some 2 billion years. And they are so profuse: In a teaspoon of healthy soil, there can be billions of microorganisms. And they have this partnership with plants, where plants capture carbon dioxide from the air—that’s what photosynthesis is all about—and turn it into a carbon fuel for their own purpose. But they also share nearly half of that carbon fuel with these microorganisms underground. So the plants are feeding carbon to these microorganisms, and that’s how carbon gets fixed in the soil. That’s how the carbon that we’ve lost in our soils got there in the first place. Even early agriculture started to disturb that carbon that was in the soil. But the kind of agriculture we have now, with deep tillage and the intense chemical use, that is the kind of agriculture that really sickens those communities of soil microorganisms."

On how healthy soil can help farmers weather climate change

"One of the things those soil microorganisms do when they take that carbon from the plants is they build structure in the soil. And the effect of that is like creating billions and billions of tiny cups and saucers in the soil. And that kind of healthy soil can hold vast amounts of water. So when it rains, the rain penetrates the soil right away and stays in the soil. Sometimes we get these rainfalls now where what we usually get in a month will fall in an afternoon. And when that happens, farmers really struggle because, if they have sick soil, that water is hitting the top of that soil and then running off and taking away topsoil and polluting streams. When farmers have healthy soil, though, that rain percolates down and stays in the soil. So they are protected both against flooding and drought."

On the financial benefits of promoting healthy soil

"The farmers that are really successfully practicing soil health techniques are not doing it just to be good global citizens. The farmer that I profiled in the middle of my book, Gabe Brown, who is a farmer in North Dakota, he started using these techniques because he couldn't afford the fertilizers and the fungicide sprays. And he started using what turned out to be soil health techniques—not using fertilizer and chemical sprays and rotating his cattle through—just because they made financial sense for him at that time. But he is producing more than the county average. So there is a huge financial benefit."

On how much carbon the soil can store

"The way that people have to think about this is that we are at 400 parts per million of carbon dioxide in the atmosphere. And most scientists say that we need to be at 350 parts per million to prevent calamitous climate change. And there are all sorts of high-tech, very expensive, very iffy schemes that have been suggested to drawdown that carbon dioxide. But the fact of the matter is that we already have a technology that does this—it’s photosynthesis. According to Rattan Lal, who is a very well-respected soil scientist, a quarter of the earth’s landmass has been degraded by human activity. And mostly that’s agriculture. So if we can start practicing agriculture that puts carbon back in the soils, then we really have a chance at surviving this environmental disaster that we’ve created. By some estimates, we can sequester enough carbon dioxide in five years to take the parts per million from 400 down to 350. That’s a very optimistic scenario. But even if we can’t sequester as much carbon in the soil as the most hopeful estimates suggest, it’s still the right step to take."