Regenerative Agriculture: Soil health and carbon sequestration

The Regenerative Organic Alliance recently announced details of its certification program. This will be of interest to viticulturists the world over so I have begun a series detailing the program, the underlying schema, and the practices. To date, I have written posts on the certification program, Regenerative Agriculture as a farming approach, and a soils-composition primer. The Regenerative Certification proposes practices in both soil health and carbon sequestration; I provide background on the convergence of both topics in this post.

Carbon is found in the soil in both inorganic and organic forms. The makeup and storage of carbon in soils (from traditional sources) are detailed in the figure below.

Soil carbon, which comprises 60% of soil organic matter, causes the soil to retain more water and results in better crop yields during droughts, a reduction in soil erosion, increased plant nutrient retention, and increased biological diversity. Higher soil carbon levels also hold soil particles together so that less erosion occurs (Pimentel and Burgess, Maintaining sustainable and environmentally friendly fresh produce production in the context of climate change, Global Safety of Fresh Produce, 2014).

The charts below show how atmospheric carbon makes its way into the soils and how it is used as currency by soil microorganisms.

Source: USDA

Microbial decomposition releases carbon dioxide so the ability of the soil to shelter some carbon from decomposition is important (Cho):

• Soil aggregates shelter carbon particles within their structures
• Aggregation happens when tiny particles of soil clump together
• Mycorrhizal fungi produce sticky compounds that facilitate soil aggregation
• They are able to transfer 15% more carbon into the soil than other microbes
• These aggregates give soil its structure
• Essential for healthy plant growth
• Soils with high clay content are also able to form chemical bonds that protect carbon from microbes

Soil Health Imperative for Increased Soil Carbon Levels
As the world's population has increased, so has the pressure on its farmers to produce the food necessary to meet this growth. But, conversely (see chart below), the world has seen a 60% loss in the topsoil over the last 150 years.  And the topsoil that remains has been severely degraded by pesticides and fertilizers.

Pesticides can harm beneficial soil organisms as well as pollute waterways with runoffs. Fertilizers harm in that they feed the plants directly, to the long-term detriment of the plant, the soils, and the microorganisms that inhabit those soils.

According to Mark Bradford, et al. (Soil carbon, source for policy and practice, Nature Sustainability), there is a "scientific consensus on the need to rebuild soil organic carbon for sustainable land stewardship."

Climate Mitigation Imperative for Increased Soil Carbon Levels
According to a Slate article, Napa grape growers are embracing "carbon farming" -- "a suite of practices designed to maximize carbon storage in the soil." According to the article, the most optimistic calculations suggest that, if implemented worldwide, carbon farming would sequester 100% of global CO₂ emissions. The Napa County Resource Conservation District is currently creating free customized plans for interested vineyard managers. Let's take a deeper look at the thinking behind carbon farming.

The earth's soils store three times the amount of carbon in the atmosphere and four times the amount stored in all living plants and animals. Human action introduces an enormous amount of carbon dioxide into the atmosphere and about 25% of that amount is returned to the soil through the photosynthetic activity of plants.

Programs like California's Healthy Soils Initiative and France's 4 per 1000 Initiative (detailed below) promote land management practices designed to build soil organic matter in order to increase carbon sequestration and reduce overall greenhouse gas emissions.

Strategies for Increased Soil Carbon Retention/Capture
Reducing the amount of carbon that is released from the soil -- plus storing additional carbon in the soil -- is seen as key to both improved soil health and the battle against climate change.

Table 1. How soils can sequester greater amounts of carbon.

Regenerative Practices	Outcomes
Cover crops (like clover and legumes)	Can compensate for carbon loss from tillage by putting more carbon into the soil
Leaving crop residue in the ground	Can compensate for carbon loss from tillage by putting more carbon into the soil
Crop rotation/diverse crops	Adds more varied biomass to the soil, and, hence, more carbon
Conservation tillage	Soil carbon not exposed to O₂ and soil aggregates remain intact, sheltering their carbon
Rotational grazing	Helps keep carbon in the soil by moving herds to new pastures after grazing, allowing old ones to renew Carbon, in the form of manure, gets spread around
Manure and compost	Increase soil productivity and the formation of stable carbon that cam remain in the soil for decades

More carbon in the soil translates to more fertile soils which:

• produce more food
• promotes biodiversity
• holds moisture more effectively
• is less vulnerable to erosion, floods, nutrient loss

There are a number of dissenting voices around the use of carbon sequestration as a tool in the battle against climate change. Bradford says that the conflation of arguments relating to climate mitigation and soil health is not surprising because many of the initiatives share carbon acquisition and soil restoration goals. But, he says further, "we submit that rebuilding soil carbon in agricultural soils should be treated as a distinct objective that is well supported by soil scientific knowledge." I note here that The Regenerative Organic Alliance Certification does have separate channels for Soil Health and Carbon Sequestration practices.

Janet Ranganortham, et al. (Regenerative Agriculture: Good for Soil Health, but limited potential to Mitigate Climate Change, World Resources Institute, 8/12/20), states that "Practices grouped as regenerative agriculture can improve soil health and yield some valuable environmental benefits, but are unlikely to achieve large-scale emissions reductions."

According to Cho, scientists at UC Irvine think that models might have overestimated -- by 40% -- the potential of soils to sequester carbon. Cho says that these studies say that there is no silver bullet and that, ultimately, the best way to combat climate change is to reduce fossil fuel use and move to renewables as quickly as possible. And the latter is the fundamental point that Bradford was making. He did not want carbon initiatives to divert attention from the real large-scale opportunities in the climate change fight.

©Wine -- Mise en abyme