Last week, 650 people from 80 countries gathered in Germany for a week-long discussion about an increasingly important topic in climate change: soil. Dubbed Global Soil Week by the Global Soil Forum — an international body dedicated to achieving responsible land use and soil management — the conference brought together scientists and environmental advocates from all over the world who hoped to translate scientific research about soil into tangible policies for its management.
2015 is shaping up to be a big year for soil — in addition to being Global Soil Week’s third year running, the United Nations Food and Agriculture Organization has declared it the International Year of Soil. José Graziano da Silva, director of the FAO, has called soil a “nearly forgotten resource,” and has implemented more than 120 soil-related projects around the world to mark the International Year of Soil. Farming First, a global agriculture coalition with more than 150 support organizations, has also called for soil health to be a top priority in the UN’s new Sustainable Development Goals.
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.
“We thought for many many years if you just increase plant productivity, soil carbon will just go up,” Kate Lajtha, professor of biogeochemistry at Oregon State University, told ThinkProgress. “What more and more models are seeing now is that the opposite is true.”
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.
Topsoil, Lajtha says, is where most soil carbon is stored — it’s where decomposed plant matter and plant roots are deposited — so losing topsoil means losing a huge amount of carbon currently stored in the soil.
But soil degradation isn’t irreversible. “If we manage the soil properly, we can reverse the degradation and some of that carbon that we lost can be put back,” Lal said.
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 continously 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.
For some farmers, switching to no-till agriculture means replacing seed drills, which can cost upwards of $100,000.
“Even though the community as a whole benefits, there might be a reduction in yield that is prohibitive to farmers that adopt it,” Lal said, noting that the adoption rate of no-till agriculture has been almost zero in places like Africa and Southeast Asia. “We have a long way to go,” he said.
Scientists have also seen promise in the practice of agroforestry — combining trees with cropland or livestock systems. Elizabeth Teague, senior associate for environmental performance at Root Capital, an investing fund that works with small agribusinesses in Africa and Latin America, have seen a slew of benefits associated with agroforestry, mostly with coffee and cocoa crops.
“Trees can help enrich the soil, and if done properly you can help avoid erosion, which is a big problem in coffee producing environments,” Teague told ThinkProgress. “Many studies have also shown that the agroforestry system can help mitigate climate change by helping with carbon sequestration. compared to other type of cropping systems, the trees are sequestering carbon and increasing above and below ground carbon stocks.”
Like no-till and cover crops, however, certain barriers still exist between small-hold farmers in developing countries and agroforestry. Planting trees alongside crops requires a certain level of finesse — plant too many trees and the crops won’t thrive; plant too few, and the environment suffers.
“Farmers have to figure out what this sweet spot is where they are maintaining a diverse, robust agroforestry system that also allows them to have a commercially viable farm,” Teague said. “For small farmers without education, resources, and technical assistance, that can be very difficult.”
To Lal, who contributed to the Montpelier Panel’s 2014 report on soil restoration, agriculture might be the problem — but it can also be the solution.
“Most of the time the perception is that agriculture is a big time problem,” he said. “Yes, agriculture done improperly can definitely be a problem, but agriculture done in a proper way is an important solution to environmental issues including climate change, water issues, and biodiversity.”