Soil and Climate Change

Organic regenerative farming is all about soil, and there is a growing body of fascinating research revealing critical information about the role soil can play in responding to the climate crisis. With this information gaining more and more attention as the climate crisis worsens, many consumers are asking: What’s so special about dirt and what are the links between soil and climate change?  

What Makes Soil Healthy?

Soil health is defined as “the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health.” Since soil itself is not alive, soil health refers to the health and abundance of the living organisms found within it.

Many food producers understand that healthy soil is extremely important in growing  quality and consistent crops, but measuring soil health can be challenging. Imagine the differences in pH levels, salinity, water infiltration and organic matter that can exist between farms or even between different locations on the same farm, and the challenge in measuring these factors becomes clear. Despite this margin of flexibility, there is still a general consensus among farmers and researchers about what healthy soil should look like. These characteristics include: 

• Sufficient depth
• Proper nutrient levels
• Good drainage and filtration to clear away any pollutants in the soil 
• Excellent water absorption and retention, also known as tilth 
• A large population of beneficial organisms living in the soil 
• Large quantities of soil organic matter, especially humus

Healthy soil performs many vital services for its surrounding ecosystem including supporting plant and animal life, filtering pollutants, cycling nutrients and providing structural support to a variety of different plants and animals. Healthy soil is also better protected against erosion, an issue which is currently damaging both our arable farming land and our water systems.

Soil’s key ingredient is organic matter, which serves many physical, chemical and biological functions. Soil organic matter (SOM) improves water-holding capacity and stores large quantities of nutrients like nitrogen, phosphorus and sulphur. SOM also boosts the cation exchange capacity of the soil, which prevents nutrients with a positive charge like calcium, magnesium and potassium from leaching out of the soil and into surrounding water systems. There are three kinds of soil organic matter, each of which plays a specific role: 

Living Organic Matter (Roughly 15% of SOM)

Living Organic Matter is mostly made up of bacteria, actinomycetes, fungi, protozoa and algae, but also includes nematodes, insects, earthworms, plant roots and small animals. They are primarily decomposers but they also build soil structure and extract nutrients.

Dead Organic Matter (Roughly 15% of SOM)

Dead Organic Matter includes recently dead microbes, old plant roots, plant residue as well as the bodies of insects and animals. It serves as food for living organic matter.

Very Dead Organic Matter (Roughly 70% of SOM)

Also called humus, very dead organic matter is well-decomposed organic matter, distinguished from dead organic matter by its dark colour. Once the organic matter has turned into humus it will continue to decompose at a slower rate. Humus increases aggregation, enhances biological activity in the soil, slowly releases nutrients and suppresses certain soil-borne diseases. Humus is also responsible for capturing the majority of carbon for long-term storage. While soil’s organic carbon stocks can hold carbon for several decades if undisturbed, inorganic carbonate, which is produced by humus, can store carbon for thousands of years. 

SOM is essential to the health of a farmer’s crops, and it is a rather delicate ecosystem vulnerable to many external factors. Things that can negatively affect the health of SOM include:

• Temperature: The ideal soil temperature for maximum SOM activity is 21.1℃ – 37.8℃. If the temperature is slightly outside that range you may still see activity at a reduced rate.  
• Oxygen: Soil microbes need oxygen and water to stay alive. When the soil is too compacted or saturated with water, SOM will struggle to survive and their activity will slow.
• Soil pH Levels: Soil can become too acidic for SOM to thrive. Bacteria and fungi activity are greatly reduced in acidic soil. 
• Soil Disturbance: When soil is disturbed such as in the process of repeated tillage, it can damage the SOM living within it.  

Healthy Soil Can Help Fight Climate Change

Removing carbon from the atmosphere is key to limiting the negative effects of climate change. Soils is our largest terrestrial carbon sink, rivalled only by the ocean in its effectiveness to store carbon. There are currently about 2,500 gigatons of carbon trapped in the earth’s soil—three times more carbon than is in our atmosphere and four times more than is stored in all living plants and animals combined. Despite these impressive numbers, soil’s potential to store carbon is vastly under-utilized since roughly 40 percent of the soil used in global agriculture is classified as either degraded or severely degraded, meaning its carbon-storage capacity is decreased. Increasing SOM in globally available topsoil could play a major role in our fight against climate change.

The 4 per 1000 is an initiative launched at the 2015 UN conference on climate change to increase global carbon levels in soil by 0.4 percent or 4 percent per year in the first 30-40 cm of topsoil. This would dramatically reduce the amount of carbon present in our atmosphere. The 4 per 1000 initiative looked at soil from 20 different countries and found that not only is this target of increasing carbon levels in the soil feasible but in some areas, the possibility for improving carbon levels exceeded this target (in some cases by as much as 10 percent) through soil building practices like cover cropping and reduced tillage. 

In addition to removing carbon from the atmosphere, healthy soil is also proving essential in combating some of the effects experienced by the climate crisis such as food insecurity caused by flooding, droughts and prolonged periods of precipitation. Healthy soil can better hold and absorb water and improve crops’ resilience to droughts and flooding.

Climate Change Hurts Soil

We know that good soil health can aid our efforts to fight climate change. But how does climate change impact soil health? Although research on this topic is still evolving, there are a few documented ways in which climate change can harm soil or inhibit its function. 

Climate Change Increases Soil Erosion

While soil erosion happens naturally over decades and centuries, human activity has accelerated this process to the point where we are losing soil at an alarming rate. At the current rate of soil erosion, we will run out of topsoil in fifty years. Climate change accelerates erosion through increased temperatures and heat waves that dries out the soil, increasing its susceptibility to wind erosion. Hotter summer temperatures can also increase the risk of forest fires, which can damage the soil and result in a faster release of carbon into the atmosphere.  

Droughts and deforestation also increase the likelihood of desertification at a rate 30-35 times greater than seen historically. During desertification, soil loses its structure entirely and plant life is no longer able to grow.  

Floods and rising sea levels are also expected to increase water erosion and coastal erosion over the next fifty years as floods become more frequent. While human activity like deforestation, excess tillage and overgrazing is the main cause of soil erosion, climate change is still one of the leading causes and as climate change steadily spirals out of our control, it is expected to become the number one leading cause of soil erosion. A study conducted by the University of Basel estimated that more than 28 billion metric tons of topsoil will be lost annually if we do not take serious action on climate change. Once soil erodes, it is no longer useful to us wherever it settles (most likely at the bottom of the ocean) —not even to store carbon. 

Climate Change Increases the Chances of Soil-Borne Diseases

SOM has been grown in a specific location and is therefore adapted to a specific climate. When disruptions to that climate alter the temperature or moisture levels, it places the soil under stress and increases its susceptibility to soil-borne diseases. 

A recent study by the University of Bonn exposed healthy soil samples to drought-like conditions and then exposed the soil to the pathogenic fungus Pythium Ultimum. The results showed that the dry and hot soil created an easy living environment for the pathogen. While healthy soil contains certain fungi and microorganisms that deflect, neutralize or consume pathogens like Pythium Ultimum before they reach the plants, the drought-induced stress killed off many of these organisms. As a result the pathogen devastated the crops in the experiment, in some cases resulting in a total crop failure. Short-term recovery from a Pythium Ultimum blight was found to be extremely rare.

It is important to note that while SOM can recover from environmental stressors like drought, the speed at which it can bounce back is determined by its local environment. Soil that came from a traditionally cooler climate like Scotland fared significantly worse in the experiment than soil from a hotter climate like Turkey. For this reason, it is suspected that SOM in alpine and cooler regions will suffer from the effects of climate change more severely than SOM from warmer climates.

We Need to Protect And Regenerate Our Soil

Our topsoil is necessary for sustaining life on earth as well as mitigating the effects of climate change. We need to protect the soil we still have while working to rebuild the health of our degraded soil so it can be protected from erosion and disease while still absorbing carbon. 

This is the goal of Organic Regenerative Agriculture, a suite of alternative farming practices designed to rebuild and maintain soil health. These practices, which have been found to improve soil health and boost carbon sequestration in numerous studies, include:

• Keeping soil covered as much as possible: When bare earth is exposed to the sun, it dries up and is more susceptible to erosion. Plant life protects soil from erosion and root systems help hold soil in place. 
• Green manures and cover crops: This helps to prompt fertility, increase SOM and nurture microbial life which is a key ingredient in building healthy soils
• Reducing mechanical disturbance whenever possible: Tillage and overgrazing can create undesirable changes in the soil composition and the SOM. Organic regenerative farming strives to reduce or eliminate these disturbances wherever possible. 
• Planting perennials wherever possible: Perennials have deep root systems that offer structural benefits and a reliable supply of food for SOM. 
• Crop biodiversity: Different plants provide different food varieties for soil microbes. Different root depths also benefit the soil structure, making it less fragile. 
• Rotational livestock grazing: Controlled grazing can stimulate plant growth and build SOM, as well as provide a more abundant food source for livestock.

Soil is much more than just dead dirt: it is essential for all life. It is fascinating to see how healthy soil can contribute to climate change solutions, and it is essentially that we learn how to protect it from the effects of climate change and deforestation. Organic regenerative agriculture can help protect and rebuild healthy soil, and implementing organic and regenerative farming practices can be a key tool for responding to climate change within the agricultural sector.

Despite the amazing potential soil has in mitigating climate change, there is few discussions about how soil carbon capture actually works. Learn everything you need to know about how soil absorbs carbon in our next article:

This knowledge article is part of our Organic Climate Solutions campaign. Check out OCO’s Organic Climate Solutions campaign, funded in part by the Government of Canada, to learn more about how farmers can reduce the environmental impact of agriculture and be part of the climate solution.