So why is soil so important?
“If you look at the global carbon created in nature under land-based systems, soil and trees are the two dominant reservoirs where carbon is,” Rattan Lal, director of the Carbon Management and Sequestration Center at Ohio State University, told ThinkProgress.
Soils — and the microbes that live within them — store three times as much carbon as is in the atmosphere, and four and a half times as much as in all plants and animals. “If the soil carbon reserve is not managed properly,” Lal said, “it can easily overwhelm the atmosphere.”
Climate change can stimulate the release of carbon from soil in a few different ways. Normally, carbon is bonded to minerals in the soil, which helps keep carbon locked in the soil and out of the atmosphere. A recent report by scientists at Oregon State University, however, found that when chemicals emitted by plant roots interact with minerals in soil, it can cause carbon to break free. This exposes the carbon to decomposition by microbes in the soil, which pass it into the atmosphere as carbon dioxide. As the climate warms, the scientists found, more carbon dioxide in the atmosphere will stimulate the growth of plants, which will in turn stimulate the production of the root compounds that breakdown carbon and soil minerals.
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The microbes that break down stored carbon are also likely to become more active in a warmer world, according to a 2014 study published in Nature. The study looked at microbes in 22 different kinds of soil from along a climatic gradient, testing samples of soil from the Arctic to the Amazon. They found that as temperature increased, the respiratory activity of the microbes in the soil also increased, releasing more carbon dioxide — and that effect was most pronounced in northern soils, which tend to store more carbon than soils at other latitudes.
Soil isn’t just useful for storing carbon — it also grows 95 percent of the food we eat, according to the FAO. But even beyond climate change, agriculture is the number one cause of soil disruption.
“What we’re seeing is probably the biggest drivers aren’t going to be those direct effects of climate,” Lajtha said. “Really, the big driver of soil carbon change is what humans are doing to the soil, and a lot of that is agriculture.”
The UN estimates that nearly a third of the world’s soil is degraded — in sub-Saharan Africa, that figure is closer to two-thirds. Degraded soils are less effective for growing crops, threatening food security in places where most of the population lives off of subsistence farming. According to the Montpellier Panel — an international group working to support national and regional agricultural development and food security priorities in sub-Saharan Africa — soil degradation costs sub-Saharan Africa $68 billion per year. If soil degradation continues at its current rate, the UN estimates that all of the world’s topsoil could be gone in 60 years.
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Conservation practices like no-till agriculture can help minimize soil degradation, according to Lal. Other practices — like planting cover crops in the winter season or continuously applying compost to soil — can also help boost soil’s ability to retain carbon.
“In some ways, it’s as simple as a disrupted soil loses carbon and intact soil with vegetation retains carbon,” Lajtha said.
But conservation practices aren’t widely adopted yet — in Ohio, according to Lal, cover crop use and no-till agriculture is practiced on just one-third of the cropland. Worldwide, such conservation practices account for only 10 percent of cropland.
Read more at Is 2015 the Year Soil Becomes Climate Change’s Hottest Topic?
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