3. Solving for Legacy CO2: Carbon Farming

Earth’s soils are its largest terrestrial carbon sink, with 4.5x the sequestration capacity of all the plants growing on land and more than 3x that of the atmosphere. More specifically, it is organic matter in the soil that is responsible for storing carbon.

Farming along the land’s contours and strip cropping.

Soil organic matter (aka SOM) is formed from a mixture of plant residues, living microbes, fungi, waste particulates called detritus, and humus formed from plant or animal tissue in the final stage of decomposition. SOM creates a rich, dynamic top layer of earth that acts similarly to a sponge, soaking up water, holding nutrients for plants, increasing air flow, supporting beneficial bacteria, and removing lots of CO2.

Since the 1850s, the expansion of mechanized agriculture and the global population have led to the degradation of billions of acres. Disturbed and damaged soils oxidize and release much of the CO2 they previously stored, which has resulted in the release of 78 Gigatons of Carbon into the atmosphere from intensive cultivation and overgrazing - equivalent to about 8 years worth of current CO2 emissions.

The loss of topsoil is not just about CO2 levels. Rural livelihoods are also eroded when the riches of the soil is lost, causing accelerated migration to cities and increased social tensions from scarce jobs, crowded living environments and poor quality of life. Lastly, food security is threatened, as local supplies dwindle and dependency on imports or food aid grows.

By working to restore SOM globally, we can support rural communities, enhance food security and help to stabilize fragile nations, all while drawing down large amounts of CO2.

Dr. Rattan Lal, one of the leading researchers of SOM as a means for carbon sequestration, estimates that restoring 50% of the soil in degraded areas would offset about 10% of humanity’s annual CO2 emissions per year, on an ongoing basis.

Before we explore how to restore soil carbon, it is important to take a brief look at the practices that led to land degradation. For simplicity, I’ll call these practices conventional agriculture or farming.

Conventional agriculture involves regular, intensive disruption of the soil through tilling and planting, which kill the soils micro-biotic life and ruins its structure over time, according to Iowa’s Natural Resource Conservation Service. Both soil erosion and compaction can occur when soil loses its structure and life.

This problem is compounded when leftover crop wastes or weeds are plowed in or destroyed with herbicides, since damaged soil is then left barren and exposed to pounding rains, scouring winds and the baking sun, resulting in soil erosion or compaction.

On top of both of these problems, conventional farming employs high amounts of synthetic herbicides, pesticides and fertilizers, which effectively kill off the soil’s microbiota and destroys its natural loamy structure. With no more life, poor structure and nutrient availability, farmers become ever more dependent on synthetic inputs to maintain yields.

Conventional farming typically plants crops in straight rows across the land, even though water follows the natural contours of the land, running across row crops and washing away topsoil.

In terms of livestock, conventional approaches focus on maximizing herd size. For free roaming herds, this leads to ecological damage from overgrazing. For confined animal feedlots, this concentrates huge amounts of manure, resulting in local air and water pollution, not to mention greenhouse gases and the breeding ground for diseases to spread.

Regenerative agriculture could be an answer to these many problems. For greenhouse gases, there would be a dual benefit: in addition to capturing large amounts of CO2, restorative land management could eliminate up to 13% of global CO2 emissions that currently result from food production. Besides CO2, water pollution and coastal dead zones would be reduced, along with local air pollution from synthetic fertilizers, pesticides, herbicides and ploughing.

So how do soils actually capture atmospheric CO2?

Carbon is the main component of SOM, helping to give soil its structure, fertility and retaining water for plants to use. Plants provide the primary source of carbon that gets stored in soils, as they take CO2 from the air to grow via photosynthesis.

Over the lifetime of a plant, whether one season or decades, it will deposit carbon into the soil by shedding tissues from its roots underground, dropping leaves above ground and eventually when it dies, as the plant body decomposes. 

Underground, organic matter matures in its decomposition process to form humus, which securely stores Carbon for long periods of time. In fact, soil carbon levels are directly correlated to the amount of organic matter in the soil. Thus, capturing CO2 from the air into soils primarily comes down to rebuilding levels of organic matter. 

Restoring soil organic matter, and capturing CO2 in soil, can be achieved through a variety of methods, which can be employed individually or in combination with one another. The method utilized will depend largely on the local climate, terrain, type of crops being grown and preferences of the farmer.

Land management practices that regenerate soil carbon have a few common aims:

• Minimize soil disturbance

• Improve of soil structure

• Protect of topsoil from the elements

• Infuse soil with organic microbes and fertilizer

• Work with the land’s natural shape

There are several regenerative practices to rebuild SOM and capture atmospheric CO2 in the soil. Here’s a brief rundown of each:

Conservation Tillage: Conservation tillage reduces the amount of mechanical mixing and turning of the soil that occurs, or eliminates soil disturbance entirely in no-till farming. Minimal or zero tilling leaves fields covered with dead plant matter from the previous harvest, which shelters topsoil from erosive weather or sun, while providing both food and structure for microorganisms. Low or no-till farming can be paired with direct seeding, where seeds are drilled directly into crop residues, in place of the disruptive process of mechanically prepared beds.

No-till farming: soybeans grow out of residue from previous crop. Credit: Natural Resource Conservation Service

Cover Cropping: A valuable complement to conservation tillage is cover cropping. Cover cropping involves seeding fields before or after the harvest season with fast growing species that replenish nutrients, such as beans or peas that pull nitrogen from the air and fix it in the soil.

Besides fertilizing fields, these cover crops also shield from excess rain, strong winds and the beating sun. When they wither naturally or are cut down mechanically, cover species add copious amounts of organic matter above and below ground to feed soil life.

Biochar: SOM can also be enhanced by the addition of biochar. Biochar is any form of dry biomass (e.g. crop wastes or manure) that has been burned in a zero oxygen environment (pyrolysis) to create a porous charcoal which retains much of its original carbon atoms. Biochar has a unique structure, including massive surface area, that effectively creates a “soil reef” upon which nutrients, water, microorganisms and fungi can be held, stored and exchanged with the surrounding soil.

Biochar can be “activated” by submerging it for a time in compost tea - a rich broth of beneficial soil microbes - before applying to the soil. This will re-infuse the soil with microorganisms, while providing a home for them to grow and spread outwards.

Contour Farming: Contour farming creates planting furrows along the natural contours of the land, channeling rainwater around, rather than down, the landscape. This protects against sheet and rill erosion,  reduces transport of nutrients downslope and slows water, allowing greater quantities to spread, sink and percolate into the soil.

This method can be combined with strip cropping, where plantings of commercially-valuable crops like corn or soy are alternated with grasses, forage or cover crops to check erosion and runoff by holding soil. Other ecosystem processes that can lead to carbon loss include soil erosion and leaching of dissolved carbon into groundwater. 

Restoring degraded in Ethiopia with terracing and vegetative cover. Credit: The Water Channel

Managed Grazing: This approach to managing livestock aims to imitate the movement of grazing animals (also called ruminants) in the wild, where herds move across the land continuously to avoid predators. Managed grazing achieves a similar effect by periodically moving animals between a series of pastures, or by reducing livestock density per acre.

Either way, the land is protected from overgrazing, when ruminants strip the land bare of vegetation, and from being overloaded with manure. Overgrazing can cause erosion or flooding, since the soil is no longer stabilized, and excess manure can cause harmful air, water and climate-warming methane pollution.

By keeping herds moving or in balance with the land, livestock can actually have a regenerative effect on the land. In a given area, ruminants will only take a few bites of forage (grass or other low-lying vegetation), deposit some manure and stomp the ground in a couple areas.

Managed grazing speeds up CO2 sequestration, since grasses regrow quickly after being grazed. Without livestock, grasses would die off and regrow once a year. With livestock grazing, grasses will regrow multiple times - meaning extra cycles of photosynthesis and carbon sequestration.

Additionally, ruminants add new organic matter to the soil in the form of manure. Their efficient digestive systems quickly transform raw vegetation into accessible nutrients for plants and microorganisms, speeding up the decomposition process and building rich soil much faster than would otherwise occur.

Finally, through their hoof prints livestock provide healthy disruption, by aerating the soil, creating pockets for water and nutrients to collect, and imprinting seeds or organic matter into the ground.

Perennial Grains: The Land Institute in Kansas is gradually developing perennial grain, legume and seed crops, whose extensive, long-living root systems would stabilize soil, increase SOM, sequester carbon and greatly minimize the mechanical disturbances necessary compared with annual crops. Their patented Kernza perennial grain develops extensive root systems that spread up to 10 feet underground, storing far more CO2, water and nutrients compared to short-lived annual crops. The team responsible for breeding Kernza claim it is one of the most “effective solutions known to sequester carbon on our productive lands”. This new whole grain can be used in snacks, cereals, flour or beer and whiskey.

Field of Kernza, a new perennial grain developed in Kanas. Credit: Kernza

Many of these methods can be combined. For example, activated biochar could complement conservation tillage, since biochar would store soil nutrients for the long term, reducing mechanical impact from artificially fertilizing the land. Or to head off dust bowls in the future, perennial grains could be planted along the contours of the land, stabilizing the soil and capturing every drop of water.

Together, these regenerative farming practices could not only play a powerful role in a broader effort to drawdown CO2, but also conserve precious topsoil and freshwater, reduce pollution from fertilizers and create resilient food systems in an era where climate disruption appears likely. For these reasons, governments ought to provide financial incentives and technical support for farmers to ensure widespread adoption of regenerative agriculture.