Can soil help us stop global warming?
Solar panels and electric cars are important innovations. But taking care of our soil may be just as important in the fight against climate change.
Fri, Feb 07, 2014 at 08:49 AM
A group of small farmers in Kenya has begun to benefit from a new revenue stream launched in January. In addition to receiving income for their crops, these small holders will soon be paid for another type of product: Healthy soil.
It's all part of a World Bank scheme that aims to reward farmers for carbon sequestration, provide a financial incentive to better manage soil, and even raise food production in the process:
Experience from 1,505 farmer groups over three years illustrates how carbon finance can promote the adoption of SALM [Sustainable Agricultural Land Management] practices and open up the carbon market to smallholder farmers. Results so far show that SALM can help increase farmers’ yields by up to 15-20%. These productivity gains from greater soil fertility help counteract the effects of increasingly extreme weather conditions.
Soil holds vastly more carbon than trees
While we often talk about how much carbon dioxide trees can absorb, it's less often recognized — at least in the popular press and eco-blogosphere — that soil, not trees, is where Mother Nature get's really serious about carbon sequestration. In fact, of the 3,170 gigatons of carbon that's stored in terrestrial ecosystems around the world, a whopping 80 percent is in the soil itself (oceans are another story entirely). Whether we're talking about a suburban garden bed or topsoil in a tropical rain forest, understanding and protecting the soil beneath our feet has never been a more pressing priority.
So how does soil absorb carbon? It's actually pretty simple.
We already know that soils are a hotbed of biodiversity, meaning they are full of fungi, bacteria, nematodes, insects and other kinds of beasties — all carbon-based lifeforms. Soil is also where the plants and animals above ground are destined for when they die. The remains of these organisms become food for other living things, primarily fungi and bacteria. As they get broken down, some of the carbon escapes back into the atmosphere as carbon dioxide, and some gets stored in the soil, both as humus, and within the bodies of the soil organisms themselves. Whenever we disturb soil, whether we are paving over a meadow or cutting down a forest, we are disrupting the ecosystems hidden in the earth. These disruptions can have profound implications.
The climate impact of tilling
Take tilling, for instance. While it's long been thought of as a prerequisite for productive farming, farmers and researchers alike have begun to rethink the practice. Because tilling exposes soil organisms to oxygen, it dramatically speeds up the loss of soil carbon. In fact Dr. John Baker, a finalist for the 2013 World Food Prize, told The World Plant Council that ploughing farm fields may be responsible for 20 percent of global carbon emissions:
“When a farmer ploughs and cultivates a paddock it releases CO2 into the atmosphere. The vast majority (95 percent) is released from soil with the other 5 percent coming from tractor exhausts. The amount of CO2 released by cultivation during reseeding can be approximately three tonnes per hectare. When you look at it from a global level, you realize that 15-20 percent of the CO2 in the world’s atmosphere comes from ploughing.”
There are, however, alternatives. No-till farming, a technique that Dr. Baker describes as "key-hole surgery" compared to the "invasive surgery" of ploughing — has been taking off from Indiana to Pakistan, with proponents claiming it can reduce fertilizer use, soil erosion and run off while increasing soil organic matter (carbon!) too. In some cases — like the farmers in Kenya — the sale of carbon credits has helped to incentivize such practices, but because of uncertainty over climate legislation and extreme volatility in carbon markets, critics have argued that monetary incentives for soil carbon sequestration can do more harm than good unless they are based on real, long-term commitments.
What to do about beef?
Arable land is not, of course, the only place where soil management makes a difference. There's a big debate going on about how we manage grazing lands too. While advocates for vegetarianism make the case that plant-based diets require less land, others have argued that meat eating isn't going away any time soon, and that many grasslands are unsuitable for arable production anyway. So what to do about all that beef?
According to Judith L. Cotter, a researcher at Washington State University, the practice of feeding cattle grain, instead of grass, reduces methane emissions, and requires less water, land and fossil fuels. These findings, however, are not universally accepted. A recent study by the U.K.-based National Trust has suggested that less-intensive grassfed cattle farms can sequester soil carbon at such a rate that it cuts net emissions by almost 94 percent. Rob Macklin, national agriculture and food adviser at the National Trust, suggests well managed cattle farms could play an important role in both food production and environmental management, while remaining almost carbon neutral:
“Maximising carbon efficiency alone is too simplistic. Many less intensive livestock systems would be classed "inefficient" on the carbon emission scale, yet are much less reliant on artificial inputs and tend to have less impacts on water quality, loss of soil organic matter and reduced biodiversity. We believe that optimised beef production — deliberately accommodating less than maximum output in order to secure stronger and broader ecosystem protection — is the best sustainable use for the grasslands in our care.”
And then there are the outliers, like "Holistic Land Management" proponent Allan Savory. In a wildly popular TED-talk, Savory argues that reintroducing cattle and other grazing animals in massive, dense herds could actually hold the secret to reversing desertification and massively increasing the amount carbon stored in the world's soils. (A claim that critics have said is vastly overhyped and far from proven.)
Forests vs. farmland
In response to massive flooding in the U.K. town of Hebden Bridge in the late '90s, under the banner of Treesponsibility, a group of residents began reforesting the steep, eroded and often over-grazed hillsides of their valley. The idea was to halt erosion, reduce flash flooding (predicted to become more common with climate change) and sequester carbon in the process by creating pockets of woodland on vulnerable land. Certainly, there are many reasons to preserve existing old growth forests, responsibly manage forest plantations, and even plant more forests where we can.
But even planting new forests, which has major advantages well beyond carbon sequestration, is not a cut-and-dried matter. In a world of finite resources and growing populations, reforesting farmland and removing it from production may mean increased pressure on farmland elsewhere. Any serious effort for large-scale, global reforestation will need to be accompanied by increases in food production elsewhere. From soilless agriculture, insect-based cuisine, rooftop farms and lab grown meat, there are some interesting ideas for doing that — but taking them to scale is another matter entirely.
Re-imagining our relationship to soil
Ultimately, there is no silver bullet to climate change, and no single answer to better soil management. But one thing is certain: we must rethink our culture's relationship to soil. If we are ever going to get a handle on climate change, we're going to have to not only slash our fossil fuel use dramatically, but restore the ecosystems which we rely on for survival. And that means understanding that soil is not dirt, but rather a complex, living ecosystem that we are only just beginning to understand — and which we ignore or abuse at our peril.
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