ploughed field with mountians in the background

More carbon in the soil than in the atmosphere

Is there more carbon in the soil than in the atmosphere? Simple enough question, but do you know the answer?

As individuals going about our daily lives, it can be hard to see beyond our noses. Each person views only a tiny fraction of the world no matter how well travelled—the most networked come into contact with a minuscule proportion of the people alive.

The risk in a narrowness of being is that the small worldview our daily living offers becomes our global view, and we miss some of the most important happenings of our times. 

Fortunately, there are plenty of ways to widen the horizon.

I always encouraged my ecology students to make sure they looked out of the window the next time they took a commercial flight or, better still,  hitch a ride in a helicopter. The perspective is very different from high up. The landscape spreads with all its many elements interwoven and messed around by humans and their machines.

Below 10,000 feet, where light planes fly, you can see where all our food is grown.

But even with a birds-eye view, there are things we cannot see.

For example, what is your answer to this question?

Is there more carbon stored in the atmosphere or in the world’s soils?

Well, the soil carbon (C) pool to one-meter depth is estimated at 2,500 Gt C, roughly about 3.2 times the size of the atmospheric pool and 4 times more than the carbon stored in plants and animals.

Roughly 1,500 Gt C is soil organic carbon (SOC), carbon from plants that is susceptible to disturbance and easy to lose. 

Typically, 50% of the SOC in the soil is lost when land is converted to agriculture which has resulted in a soil organic carbon debt of 116 Gt SOC. This loss of SOC in cultivated soils is from a combination of erosion, lower C inputs, reduced stabilisation of SOM due to deteriorated soil aggregation, and mineralisation promoted by increased soil temperature and aeration. 

In short, agriculture messes with soil. 

We owe nature roughly 10% of the soil carbon it once had.

The good news is that what management takes away, alternative management can restore, at least in part. 

Research has shown that up to two-thirds of soil organic carbon lost is restored by one or more of the following management actions 

  • retaining vegetation cover on the land
  • conservation tillage 
  • cover cropping 
  • reducing inorganic inputs
  • addition of organic manures 
  • soil amendments (eg biochar)
  • mulching
  • soil fertility management 
  • agroforestry 
  • rotational grazing

And there are many others that, alone or in combination, can enhance SOC.

The what, how and when of restoration depends on soil type, climate conditions, and local history of land management. Decisions for repair are a science and a skill in itself but nearly always achievable.

What management taketh away, alternative management can give back under the basic rule of thumb that more organic material has to go into the soil than is taken away through agricultural practices

Research suggests that the potential exists to sequester into the soil more than half the lost soil carbon stocks in cultivated soils. Cropped soils should be able to sequester carbon for at least 20 years before arriving at a new SOC equilibrium.

The consensus is such that there are even policy initiatives that can help make this happen. For example, the  4 per 1000 initiative on Soil for Food Security, officially launched by the French Ministry of Agriculture at the UNFCCC Conference of the Parties (UNFCCC COP 21) in Paris, included a target of 3.5 Gt C annually sequestered into soils.

Photo by Slawek K on Unsplash

Why repay the SOC debt

The buzz is always about climate change and the need to curb emissions and reach carbon neutral by 2050.

Given the tonnage lost and potential for recovery, it’s no surprise that legislators are finally looking to soil as one of the options to reach what is a stretch target. They have to clutch at all straws to remain credible.

The politicians don’t seem to realise that replacing as much SOC into degraded soils as humanly possible is critical to future food security. Fail to achieve food security, and society descends into chaos.

Research over many decades has established that soil fertility, health, and functioning are immediate consequences of the amount of soil organic matter (and hence carbon) a soil contains.

And when we say function, we mean food production.

Research also tells us that an increase in SOC improves the physical properties of soil and related ecosystem services, such as better water infiltration, water holding capacity, and potentially increasing agricultural productivity and ecological resilience.

This is even more important for degraded soils that have lost carbon over time due to management.

It is tempting to default on debt—but with this one, the soil carbon debt, default means collapse.

Photo by Roger Bradshaw on Unsplash

What sustainably FED suggests

We have always been advocates for soil organic carbon. 

SOC is both the fuel and the substrate that makes plants grow well, and every soil on earth produces more biomass if its SOC is at or near potential.

We even put our healthy scepticism aside to advocate for looking after soils, particularly SOC. In our opinion, societal collapse is inevitable unless everyone starts looking after the soil.

But we cannot expect commuters on the 7.43 am train to Central station to see SOC from the window of the train or to see what was on the land of our cities now paved over. In everyday life, many critical resources that make our lives possible are not visible and are easy to ignore.

More than this, the way that nature works is hidden too. 

However, the commuters know that the atmosphere has more greenhouse gas than it did 100 years ago because humans have been very busy using energy, making stuff and more humans. As a result, the climate is changing.

Human activity has made soil a source of greenhouse gas for hundreds of years. But it is possible to change agriculture to make the soil a carbon sink, at least for a time.


Hero image from photo by Roger Bradshaw on Unsplash

Mark

Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

Add comment

Follow us

Don't be shy, get in touch. We love meeting interesting people and making new friends.

Most discussed