Keywords

Industrial farming systems succeed in producing large quantities of food for global markets. But this leads to various adverse effects, such as significant soil erosion, biodiversity loss, and pollution of water bodies (Mateo-Sagasta et al., 2017; Mekonnen & Hoekstra, 2015; Moss, 2008). They also promote high dependence on agribusiness and its products, lead to high freshwater and nitrogen consumption, and result in up to 34% of all anthropogenic greenhouse gas emissions (IPCC, 2014; UNEP, 2017). Population growth, climate change (with increasing incidence of weather extremes such as droughts and storms), potential shortages of mineral fertilizers (such as phosphorus), soil erosion and decline in soil fertility, high dependence on fossil fuels, decline in pollinators, and other factors collectively pose a major challenge to the current agricultural system.

Might there be alternative approaches, employing a set of diverse tools, able to increase soil fertility and to regenerate soil resources—creating win-win solutions such as sequestering carbon in soil to mitigate climate change? A whole range of new and innovative approaches for such purposes are presented on the following pages.

Soil and Humus Loss Through Industrial Agriculture

The “modern” or “industrial” agriculture of the early years of the twenty-first century faces many problems and challenges. One of the largest—albeit less noticed in our society—threats to humanity and the planet is the loss of soil and hence of soil fertility through agricultural practices. The fragility of the thin layer of topsoil, which is the basis for almost all that grows and almost all we eat, thus calls into question the “sustainability” of industrialized farming. In many regions of the world, soil fertility has been declining for decades; large quantities of fertile soil have been (and continue to be) washed into rivers, lakes, and oceans—disappearing forever. Soil degradation leads to the production of carbon dioxide (CO2), which is produced by the oxidation of soil organic matter (SOM, commonly known as “humus”) and released into the atmosphere. All this also has significant economic impact.

Each year, we lose around 24 billion metric tons of fertile topsoil on our fields; 10 million hectares of arable land are degraded annually as a result (FAO and ITPS, 2015; Pimentel & Burgess, 2013). The lost topsoil would fill 192 million rail cars; the degraded area is nearly the size of Greece—every year! In the U.S., the loss is 15.7, in Europe 2.5 metric tons per hectare per year (Panagos et al., 2015). “Overall, soil is being lost from agricultural land 10–40 times faster than the rate of soil formation, threatening humanity’s food security” (Pimentel & Burgess, 2013). In addition to the loss of topsoil, there are other processes impairing soil quality, with the result that around 25% of the Earth’s agricultural land is now considered degraded (Bai et al., 2013).

Around one third of the CO2 released into the atmosphere by human activities between 1850 and 1998 came from agricultural activities (Houghton & Nassikas, 2017). EstimatesFootnote 1 of carbon released since the beginning of agriculture due to soil erosion and loss of soil organic matter from forest clearing and burning range from 133 to 379 billion metric tons (Le Quéré et al., 2016; Sanderman et al., 2018). In cultivated soils, about 50–70% of soil carbon has been lost (Machmuller et al., 2015). Agricultural land today often contains less than 2% humus, whereas at the time of conversion from grassland or forests it still contained 8–15% or more.

The key question is: can excess CO2 be recycled from the air and stored in the soil, thus helping to mitigate climate change? This is a crucial issue because scientists have calculated that extensive terrestrial removal of CO2 from the atmosphere through controlled biomass and soil carbon sequestration is required to avoid the currently projected temperature increase.

How Much Carbon Can Soils Absorb?

The amount of carbon in the atmosphere is about 860 billion metric tons, and there are 450–650 billion metric tons in the biological pool (Lal, 2004). One study put the global stocks of soil organic content (SOC) at about 850, 1800, and 3000 billion metric tons in relation to the top 30, 100, and 200 cm respectively (Sanderman et al., 2018). According to the area classified as arable land by the International Geosphere Biosphere Programme (IGBP), this corresponds, respectively, to an average of 60, 130, and 200 metric tons of carbon per hectare. Soils thus store far more carbon than plants, especially in boreal forests, wetlands (especially peatlands), and grasslands (especially temperate steppes) (Fig. 1). Soils used for agriculture usually contain only small amounts of carbon or humus, and the trend is downward.

Fig. 1
A bar graph plots carbon in tons per hectare versus ecosystems. The value above the ground is the highest for the tropical forests at 150. It is followed by boreal forests, temperate forests, wetlands, and tropical savanna. The value below the ground is the highest for wetlands at 700. Approximated values.

Underestimated soils: average amount of carbon stored in vegetation and soils (up to 1 m depth) in different ecosystems—in metric tons per hectare. (Data from IPCC (2021))

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The average historical loss is estimated at 20–30 metric tons of carbon per hectare in forests or woodlands and 40–50 metric tons in steppes, savannas, and grassland ecosystems. On average, the conversion of (previously unused) grassland into cropland leads to a loss in carbon content of about 50% (Lal, 2018).

The best-known carbon sequestration initiative “4p1000” (see also section “Policy Implications”) has calculated that with a SOC increase of 0.4% per year (or 4p1000, hence sometimes called the 4p1000 initiative) in all land uses, including forests, the CO2 concentration in the atmosphere could be effectively reduced. Based on the baseline values used in its calculation, an additional 2.8 billion metric tons of carbon could be stored each year in the top 30 cm of soil (Soussana et al., 2017). This would lead to a net reduction of CO2 in the atmosphere because the current annual increase in CO2 emissions worldwide is “only” about 200 million metric tons of carbon.

Equally important ecologically, however, is that increasing the carbon content of the soil leads to many other benefits that improve crop and pasture yields. It

  • Increases available water capacity,

  • Improves the nutrient supply of the plants,

  • Restores the soil structure, and

  • Minimizes the risk of soil erosion.

Estimates for carbon sequestration through improved practices vary considerably, as the understanding of interactions and especially the knowledge of soil response is still limited. Various studies show theoretical potentials of 0.8–8 billion metric tons of carbon per year (NAS and National Academies of Sciences, Engineering, and Medicine, 2018; Griscom et al., 2017; Lal, 2016a, b, 2018; Minasny et al., 2017; Paustian et al., 2016; Smith et al., 2008; Zomer et al., 2017), while more realistic values are probably in the range of 1.5–2.5 billion metric tons. Given global CO2 emissions from fossil fuels and industry of 9.9 billion metric tons (plus 1.3 billion metric tons from land use changes such as deforestation), the potential for carbon sequestration through regenerative agricultural practices is promising.

But the conditions for implementation are not the same everywhere. Funding and cooperation among scientists, policy makers, practitioners, and various other stakeholders is needed. Global efforts to gradually change land use practices are not easy to implement, which reduces the theoretical mitigation potential. Furthermore, the sink capacity of soils is not infinite—and it is reversible if not managed properly.

Humus Formation in Theory …

Humus is not stable. Build-up and decomposition processes are characteristics of an active and diverse soil life. The various humus compounds have different durations, which can range from weeks to decades. Increasing warming due to climate change tends to lead to faster decomposition due to increased activity of soil organisms and thus makes humus build-up more difficult.

Humus-forming agricultural practices (Fig. 2) include a broad crop rotation, the use of catch crops, of nitrogen-fixing legumes, the use of plant species and varieties with greater root mass and deeper roots, the integration of animals into the cropping system, agroforestry systems, improved grassland management, leaving crop residues and additives such as manure, compost, and biochar (see box below) (Lal, 2010, 2016a; Minasny et al., 2017; Griscom et al., 2017; Paustian et al., 2016; Lugato et al., 2014; Soussana et al., 2017).

Fig. 2
A graph of area of practice adoption versus average greenhouse gas emission reduction. Biochar application is the highest with area of practice at 10000 and greenhouse gas emission between 0.1 to 1. Restore histsols are the lowest with area of practice at 10 and greenhouse gas between 10 to 30. Approximated values.

Global carbon sequestration potentials for various agricultural practices. (Data from Paustian et al. (2016))

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Increasing humus levels and adapting agricultural practices accordingly requires a deep understanding of the fundamentally important relationships between plants and soil life. Plants interact intensively with various microorganisms, especially with certain microbes and fungi in the soil. A single gram of healthy soil contains more bacteria, fungi, and other microorganisms than there are people on earth. These influence plant growth and health as well as nutrient and water storage in the soil (Bardgett & van der Putten, 2014; Cao et al., 2011; Eisenhauer et al., 2017; Steinauer et al., 2016). The underground “wood wide web” shares nutrients and water with the plants and receives signals from them, which influence the defense against insect predators and leaf-infesting fungi. Plants in turn transfer and share 20–30%, sometimes even 50% of their photosynthesis products (mainly carbohydrates, but also amino acids) via root exudatesFootnote 2 with this very diverse life system (Eisenhauer et al., 2017; Jones, 2008; Leigh et al., 2009; Steinauer et al., 2016), and thus form a complex natural symbiosis. Plant diversity and soil microbial diversity interact positively, supporting plant health and plant mineral concentrations. “In fact, roots and their plant health-promoting microbiome may hold the key to the next green revolution” (Pieterse et al., 2014).

Biochar as a Carbon Sink

Biochar,Footnote 3 produced by pyrolysisFootnote 4 from biomass, is a long-term stable form of carbon. Biochar has abundant advantages, many of which are not yet understood. It is resistant to decomposition (Lehmann et al., 2015; Zimmermann & Gao, 2013) and can stabilize organic matter added to the soil (Weng et al., 2017). Biochar can also create long-term carbon pools in the soil (Griscom et al., 2017; Paustian et al., 2016; Soussana et al., 2017; Woolf et al., 2010). Its use offers a range of benefits for soil fertility and quality, such as the promotion of fungal and bacterial growth, improved water and nutrient retention, reduced impact of pathogens, (Lehmann et al., 2011; Hagemann et al., 2017), and even higher crop yields (Jeffery et al., 2011; Kammann et al., 2015). Plant biomass, after subtracting water, consists of about half of the carbon that was removed from the atmosphere through photosynthesis during the plant’s growth. If the plant dies, it begins to biodegrade, with the absorbed carbon returning to the atmosphere in the form of CO2. To prevent this, biomass can be carbonized. To do this, it is pyrolysed, that is, thermally treated at a temperature of at least 400 °C in the absence of air. This way, much of the biochar is bound into molecular structures that can remain stable in soils for many centuries. The product of this pyrolysis process, biochar, is seen as a way of limiting anthropogenic climate change.

Biochar is used especially as a soil conditioner and carrier matrix for fertilizers and as a feed additive, stable bedding, and manure additive. For some years now, new fields of application have been emerging outside agriculture, for example in the construction and plastics industries, where biochar improves the functional properties of concrete and plastics, or in water and air pollution control, where it can replace conventional activated carbon made from fossil raw materials. Biomass and the biochar produced from it are thus increasingly becoming lucrative agricultural (by-)products that are also used in industry and environmental technology. What all applications have in common is that the biochar is not burned. The carbon (C) content of the biochar, which had been removed from the atmosphere, thus remains stored in the terrestrial system for the long term. The transformation of biomass carbon into biochar as well as pyrolysis oils is the only already available climate technology that has been extensively tested, can be quickly scaled up globally, and can establish and stably maintain relevant carbon sinks for many centuries. In contrast to all comparable technologies, the biochar industry is already in exponential growth and offers multiple added values that go beyond pure carbon storage. To limit climate change to 2 °C, at least 220 billion metric tons of carbon will need to be stored in additional sinks by 2100—equivalent to around 800 billion metric tons of CO2. To achieve a third of this sink capacity using biochar and pyrolysis oil, around 400,000 industrial pyrolysis plants would need to be commissioned worldwide by 2050. However, to construct such an enormous number of industrial plants so fast, sustained exponential growth in plant construction over the next 20 years would be needed, from around 100 plants per year presently to some 50,000 plants per year at the peak.

Even more difficult than increasing the capacity for industrial construction of pyrolysis plants is raising the biomass productivity of agriculture in such a way that sufficient feedstock can be provided each year for the production of biochar. This goal can be promoted by using methods such as agroforestry, forest pastures, forest gardens, humus build-up, and mixed cropping, which produce food and biomass simultaneously through multiple uses of the land. With algae farms, additional ocean areas can be developed for biomass production. The essential increase in biomass capacity can also be promoted precisely through the application of biochar, namely by using plant-carbon-based fertilizers. This method mixes biochar with dissolved nutrients so that the nutrient-rich solution is completely absorbed by the pore system of the biochar. So far, nutrient solutions have mainly been of organic origin, such as cattle urine, biogas slurry, press water from tofu production, but also compost extracts, or other commercial liquid fertilizers. In principle, synthetic and mineral fertilizers can also be used. Biochar acts here primarily as a carrier matrix for nutrients, reducing their leaching and improving their uptake by plants as well as the charge equalization between roots and soil.

Affording substantial efficiency gains, the combination of organic fertilizers with biochar offers a promising prospect, especially for organic farming. A 2020 meta-study was the first to evaluate scientific publications that examined exclusively the effects of combining biochar and fertilizers (Ye et al., 2020). The authors could show that biochar is not only an aid for tropical agriculture but, if used correctly, leads to significant yield increases in temperate climates as well. Compared to fertilization with the same amount of nutrients without biochar, the application of biochar fertilizers resulted in an average yield increase of 15%.

In the tropics, average yield increases of 25% can already be achieved with biochar (Jeffrey et al., 2017). Even 50% yield gains were achieved with biochar-based organic fertilizer applied directly to the root zone of vegetable, fruit, and cereal plants (Schmidt et al., 2017).

Evaluation of 26 meta-analyses, which included 19,000 data sets from over 1500 scientific publications, show that the use of biochar improved all 66 investigated agronomically relevant parameters by an average of over 20%. It increased yield and plant health, biological soil activity, root growth, water use efficiency, and humus content while also reducing greenhouse gas emissions. Depending on the climate zone and the crop grown, the use of biochar-based fertilizers can not only improve ecosystem services but also increase yields by at least 10–25%. If we were to apply biochar to the entire global agricultural area of 51 million square kilometers, the yield gains would mean that at least 10% less land would be needed to produce the same amount of food and feed. On this freed-up land, a wide range of carbon sequestration measures could be applied, from reforestation to the production of biomass for producing biochar. The latter should ideally be integrated into the remaining crops to achieve structures that are suitable for increasing biodiversity, stabilizing soils, and creating a balanced microclimate.

At a productivity of 10 metric tons of biomass (dry matter) per hectare per year, the above-mentioned 10% of global agricultural land could produce 5.1 billion metric tons of biomass—which could be converted by pyrolysis into 1.7 billion metric tons of carbon.Footnote 5 Over a 50 year period, this would amount to 85 billion metric tons of carbon or just under 400 billion metric tons of CO2e, about half of what would be minimally needed by the end of the century to prevent dangerous climate change. Since significantly higher yield increases and thus land savings in favor of biomass production can be expected in the tropics, the estimated potential of 400 billion metric tons of CO2e is entirely realistic.

In pointing out all these potentials, it is important to note, to insist, that any food competition is excluded. For any land taken out of food production, there must be a substitute or else yield increases, based on sustainable land management, must be achieved on the remaining land.

If food neutrality is ensured, the use of biochar technology is a promising option that also optimizes various ecosystem services. Specifically, it reduces

  • Nutrient leaching and groundwater contamination,

  • Emission of greenhouse gases from agriculture, and

  • The uptake of pollutants by plants.

In addition, it improves

  • Water storage of soils,

  • The resilience of agricultural systems, and

  • The buildup of humus, which removes additional carbon from the atmosphere.

In conclusion, it should be admitted that the implementation of the biochar approach is complex. In many places, experts, authorities, advisors, industries, and not least farmers would have to show good will. Still, half of the additional carbon sinks needed to save the climate could be created around the world—with an investment of only 500 billion euros, 50% of the world’s annual military spending (Roser et al., n.d.). The emission reductions agreed for the period till 2050 must, however, be achieved in addition, as a necessary precondition for a climate-neutral carbon balance.

Whereas metabolic products of bacteria as well as their cell bodies make up an important part of the soil’s carbon pool, fungi that establish symbiotic relationships with plants (mycorrhizae) produce a sticky, carbon-rich glycoprotein known as “glomalin,” which is crucial for soil stability and water storage and forms an important carbon reservoir—carbon that has been taken from the atmosphere. Moreover, through their exsudation, roots increase the carbon pool by more than twice what the composting process of dead above-ground biomass can do (Kätterer et al., 2011).

Because a system with a higher carbon return also results in more nutrients being returned to the plant, plant productivity is increased and the need for fertilizer is reduced. In conventional agriculture, chemical fertilizer is one of the main sources of greenhouse gas emissions through both its energy-intensive production and the resulting reaction of microbes. It is important to note that “the gain [of regenerative farming systems] is positively correlated with soil organic matter” (LaCanne & Lundgren, 2018). It is unsurprising therefore that humus losses can lead to an enormous social loss of natural capital.

… and Humus Formation in Practice

The following agricultural practices can help sequester carbon in the soil:

Because ploughing the soil is one of the main drivers of humus mineralization and soil erosion, switching to practices that reduce or avoid ploughing can have a positive impact on soil organisms and carbon levels, saving up to 70% of energy and fuel expenditures and of investments in machinery. Under most “no-till” systems, which avoid ploughing before sowing, carbon increases in the upper soil layer (up to about 10 cm depth) and partially decreases below that (Mäder & Berner, 2012; Powlson et al., 2014). Nonetheless, research shows that the activity of bacteria, especially fungi, is increased, and soil structure often improves. No-till helps protect soils but is often combined with the use of herbicides, such as glyphosate, which can have negative effects on soil biology and other living organisms as well as on human health. To benefit from no-till and to store additional carbon, this practice must be integrated into more diverse agroecosystems, for example through the use of green manure mixtures that help loosen the soil with deep-reaching roots, transfer carbon to the rhizosphere, stabilize soil aggregation, and suppress weeds and pests.

Management practices that can store additional carbon include selecting crop species and varieties with greater root mass and deeper roots, using crop rotations with greater carbon inputs, using catch crops during fallow periods, leaving crop residues on the field, and additives such as compost and biochar. Intercropping (the simultaneous production of multiple crops on the same area of land), increased crop rotations and catch crops can improve soil fertility by covering the soil, feeding the microbiome year-round, fixing nitrogen in the soil by nitrogen-fixing plants, and thus increasing soil carbon content (Poeplau & Don, 2015). Such crops also reduce soil erosion and suppress weeds and pests. For example, it has been calculated that through use of catch crops two million metric tons of carbon per year could be stored away in France (Pellerin et al., 2019). Increasing the diversity of crop species both within a crop and between successive crops can lead to significant economic gains (higher yields, less pesticide use) through greatly reduced weeds and insect pests, as this positively changes the supply of natural enemies (e.g., aphids) (Lundgren & Fausti, 2015). Plant species with deep roots (particularly useful for catch crops) can play the following key roles: sequester more carbon, break up plough seals, use the subsoil for additional nutrient enrichment, aerate the soil, create favorable conditions for earthworms and other soil life, and positively influence the root diameter of the next crop.

Earthworm abundance is an important indicator of soil activity and soil health. Improving their living conditions is crucial as they dig (bio)pores that help aerate the soil, infiltrate water, and store it quickly. In addition, through their activity and nutrient-rich excretions, they increase humus content by integrating organic matter into the soil and facilitate access to the nutrient-rich subsoil. Leaving crop residues and mulching with biological material are important approaches to increasing soil fertility and soil carbon while limiting soil erosion.

Mixed or intercropping, that is, the simultaneous cultivation of several crops on the same area, can increase net plant growth and thus sequester more carbon into the soil, increase yields, and reduce weeds at the same time. This can be explained by a larger leaf surface, increased mycorrhizal activity, increased communication and exchange via root networks, and complementary demands on the soil (plant species use different mineral nutrients in diverse quantities) (Walder et al., 2012; Brooker et al., 2015).

Undersowing helps protect the soil when the main crop does not completely cover the soil. Such “living mulch” helps suppress weeds and can promote the growth of the main crops. The use of legumes in undersowing can provide additional organic nitrogen while increasing soil carbon content.

Another factor is that in the temperate regions the potential photosynthesis rate is highest during the summer months. But, with cereal crops maturing, this energy is not being used for producing carbohydrates. The undersown crop, by contrast, remains photosynthetically active at this time of year, producing carbohydrates among other things, thereby adding carbon to the soil while providing nectar, pollen, and seeds to insects and birds while also enhancing biological pest control.

The application of compost to cropland and grassland stimulates both above- and below-ground net primary productivityFootnote 6 and, even with only one application, can lead to carbon accumulations of two to five metric tons per hectare in subsequent years (Ryals & Silver, 2013). It increases soil life through the fungi and bacteria in the compost itself. And it stimulates soil life activity while adding extra carbon and nutrients to the soil, which improve the soil’s structure and water storage capacity.

Native Pastures: often pastures are regularly cultivated with shallow-rooted species (such as Kentucky bluegrass in the U.S.) and with a low diversity of grasses. But the “natural” prairies of the U.S. (as well as Europe’s steppe regions) consisted of a variety of native plants, many of which were deeply rooted into the soil and therefore stored carbon (Teague et al., 2016). While typical seeded grasses reach depths of no more than 50 cm, native plants easily go down several meters, with different root forms occurring and complementing one another.

Combining livestock and cropping, that is, using animals to graze catch crops or stubble, creates synergies between system components, which can improve resilience and sustainability while fulfilling multiple ecosystem functions. It can increase both humus content and economic yield, diversify agricultural production systems, improve drought resilience, and reduce soil erosion (Bonaudo et al., 2014; Franzluebbers & Stuedemann, 2008, 2014). The use of grazing animals not only improves the soil through their bacteria- and nutrient-rich excreta, but can simultaneously replace the use of herbicides (such as glyphosate). “Cereal-pasture mixed cropping systems” (pasture cropping) go one step farther; they combine perennial pastures with annual crops and deliver impressive results in terms of increased soil carbon content (9 metric tons of carbon per hectare per year for the years 2008–2010), biodiversity, and yields (Seis, 2006; Glover et al., 2011).

Improved grassland management, such as lower stocking densities, different types of rotational or short-term grazing, seasonal grazing, inclusion of legumes and a variety of crops, can lead to sequestration of up to 1.8 billion metric tons of carbon annually (Paustian et al., 2016; Teague et al., 2016). Especially effective is adaptive multi-paddock (AMP) grazing (also called holistic grazing management or mob grazing), where herds graze in a rather small plot for a very short period (usually from half a day to 2–3 days) before being led to the next plot, with grazed plots given several weeks or months to regenerate after grazing.

In contrast to a continuous grazing approach, where the net impact of carbon reduction can be offset by N2O and CH4 emissions from animals and their excreta, there is new research and an increasing number of practitioners reporting gains in humus content, soil fertility, biomass, and plant diversity. There is a net gain in carbon even when the methane emissions from animals are taken into account (Teague & Barnes, 2017).

Best Practice Examples

Gabe Brown is a prominent conventional farmer in the U.S. who has turned his farm, formerly based on a monocultural model, into a productive operation. With reduced herbicide use, he has managed to increase the water-holding capacity and humus content of his soils. While he had less than 2% humus in his soils in the early 1990s, he now enjoys contents of more than 6%. Brown uses a wide crop rotation with diversified intercropping, has integrated livestock into his cropping system through a holistic grazing management plan, and has stopped ploughing his fields (Brown, 2020). Another well-known North American farmer, Joel Salatin, makes intensive use of mob grazing technology, which he has expanded to include a so-called follower system in which different animals such as cows, sheep, chickens, and turkeys follow one another according to their feed needs and take turns. This greatly increased the fertility of his soils and the plant diversity on his meadows (Polyface Farms). In Germany, Michael Reber, a farmer from Schwäbisch-Hall, has been able to completely dispense with the use of fungicides and insecticides in recent years by implementing measures such as minimum tillage, diverse catch crops, and mixed crops in the entire crop rotation. He uses herbicides only for maize, when necessary. The use of mineral fertilizer is also being further reduced each year by upgrading the organic fertilizer available on the farm. The aim is to cultivate all crops as mixed crops and, in the medium term, to integrate animal husbandry back into the farm’s land use (Reber, 2017).

Agroforestry, that is, the integration of trees and shrubs into cropland and livestock systems, can bring multiple environmental, economic, and social benefits. First of all, it has a positive effect on humus content: between 0.2 and 5.3 billion metric tons of carbon per year can be fixed in soils (in addition to carbon bound in wood), with the best results achieved in the tropics and subtropics (Griscom et al., 2017; Shi et al., 2018). In addition, other positive “side effects” are also at work here, from increased biodiversity to diversified yields. Agroforestry and conservation agriculture approaches in sub-Saharan Africa and tropical countries showed that often significantly larger increases in soil carbon levels are achievable than “only” 0.4%, while delivering higher economic and environmental value (Corbeels et al., 2018). In short, integrating trees into regenerative agricultural practices or holistic pasture management can increase rates of carbon sequestration by a factor of 5–10 and soil carbon stocks by a factor of 3–10 (Toensmeier, 2018).

Finally, it is possible to develop intensive silvopastoral systems (combining trees, animals, and pastures) that not only lead to more humus in the soil but also to a net sequestration of 4–12 metric tons of carbon per hectare per year—offsetting the methane production of the animals. In addition, the production of meat and milk can be increased (Montagnini et al., 2013).

Policy Implications

There is some progress around the world. The Australian Coalition Government has in the years 2018–23 invested around $450 million in a Regional Land Partnership Program plus $134 million in a Smart Farms Program to improve soil health. The Andhra Pradesh government has launched a Scale-Out-Plan to convert six million farms/farmers to 100% chemical-free agriculture by 2024. This program is a contribution to the United Nations Sustainable Development Goals. Late in 2020, the EU has presented a soil strategy and announced a “Soil Health Law” for 2023.

Putting the above methods into practice is a challenge, of course, because it requires much knowledge and must be adapted to local conditions. Some of these efforts will require several years of persistent implementation to achieve reliable results and to overcome concerns about financial risks and other criticisms from the more conservative farming community. There is already a small but growing number of farmers successfully using these techniques. It is increasingly likely that others will follow. Interest in field days by these innovative farmers is steadily increasing around the world.

An important conclusion is that only a combination of approaches can help mitigate climate change. But it is even more important to show how agricultural practices that increase soil organic matter also support improved food production, greater biodiversity, increased water storage and drought resilience, and other important ecosystem services, thereby creating a win-win solution for farmers and society at large. The current structures underpinning the “industrialized agricultural system” are complex and well-established, involving farmers, machinery, and chemical manufacturers, markets and trade, taxes and subsidies, not least resulting in low consumer prices. A broad implementation of the approaches described above can only be achieved with the active support of governments, while the development of the regenerative agricultural movement is currently mainly bottom-up.

Although many of the practices described come with costs, some of them will generate revenue and cost savings. The costs we are willing to bear for them determines the amount of carbon removed from the atmosphere. Price tags vary but suggest that at $20–$100 per metric ton of carbon much of the technical carbon sequestration potential could be realized (UNEP, 2017; McKinsey & Company, 2009).

The Five Principles

… of carbon storage in soil and regenerative agriculture are based on the motto “do as nature does”:

  1. 1.

    Protect the soil surface,

  2. 2.

    Minimize soil disturbance,

  3. 3.

    Use a high diversity of plants and animals,

  4. 4.

    Preserve living plant-root networks,

  5. 5.

    Integrate animals into arable farming

Taking this into account, the following cross-cutting measures should be prioritized by policy makers whenever the aim is to increase humus content and thus to transfer carbon back into the soil:

  • Combat soil degradation and support land regeneration. Agricultural practices have reduced soil fertility and degraded large parts of the land surface. Given the regenerative powers of nature, such areas can, with suitable expertise, be restored.

  • Promote agroecological practices that increase the amount of humus and pay farmers for storing carbon in the soil. A small but growing number of farmers are using various innovative methods that use nature as a model for increasing humus levels and thus many other “ecosystem services.” These best practices should be supported, communicated, and, if successful, widely disseminated, at both the national and international levels.

  • Popularize agroecology and holistic food system approaches in politics, education, and research. Holistic thinking in the above-mentioned methods can be seen as a paradigm shift in the agricultural sector which, however, impedes an instant breakthrough. Knowledge about these agroecological approaches should be promoted through politics, education, and research to enable a faster and more efficient transition.

  • Improve knowledge, communication, training, and networking of/for practitioners to increase humus content, sustainable soil management, and agroecological practices and approaches. The dissemination of this knowledge currently happens through local initiatives and small regional to international networks. Governments and other institutions should support these efforts toward a new future for agriculture.

  • Focus not only on yield, but also on other “ecosystem services” that farmers can contribute to (carbon sequestration, climate regulation, water storage and filtration, erosion control, biodiversity, nutrient-rich food, and others). Our current system mainly looks at the parameter “yield per hectare” as an indicator of success, neglecting other important factors of sustainable practice. These should be made more prominent through education.

  • Successively restructure fossil-energy and agrochemical subsidies to encourage diversification of agroecological practices. The current practice of industrial agriculture is heavily dependent on inputs and threatens the underlying basis of its own production system—soil, biodiversity, water, and climate. Shifting the focus to diversified agroecological practices can help promote the very resources we depend on to produce diverse and healthy food.

  • Support agriculture and forestry as sectors that can potentially contribute to climate change mitigation. Agriculture and forestry can be important sectors for climate mitigation as they have the potential to store large quantities of carbon in the biophysical realm, while providing important benefits to our society.

  • Support campaigns to conserve and revitalize soils, such as SaveOurSoils and 4p1000. There are several international initiatives working to promote this issue as part of the political agenda.

The 4P1000 Initiative

… is the most prominent and politically active movement to advance the issue of carbon sequestration in combination with agroecological practices.

Launched by France at COP-21 in December 2015, this initiative brings together public and private sector stakeholders (local, regional, and national governments, businesses, trade organizations, NGOs, research institutions, etc.) under the Lima-Paris Action Plan (LPAP). Over 40 countries and over 1000 institutions and organizations worldwide have joined this movement. The 4p1000 initiative provides a space for collaborative interaction among scientists, policy makers, and practitioners to ensure that actions are scientifically sound. The initiative is very active at the policy level and promotes science, as it has also proposed a research program to support the initiative’s goals. In addition, Regeneration International, a cooperation of more than 350 companies, farmers, and institutions, is working to raise awareness and scientific knowledge in this area and on the application side.

  • Help initiate emissions trading and/or expanding it to new sectors such as agriculture and agroforestry. Although the success of existing emissions trading is limited, a prominent concern on our political agenda should be to integrate agriculture and forestry into existing systems and to adapt them to promote regenerative practices that support carbon sequestration.

  • Develop strategies for the provision of agricultural products that promote sustainable land management through public procurement where appropriate. The transition to sustainable land management practices may increase costs and/or reduce returns to farmers in the early years. As the current economic model does not usually factor land degradation into the cost of production, farmers should receive support from governments, markets, and consumers to develop appropriate farming practices.

  • Improve research for soil carbon sequestration methods to generate knowledge to support action. Best practices must be identified, monitored, verified, publicized, and promoted with science-based harmonized protocols and standards to increase reliable knowledge of successful approaches.

The potential for carbon sequestration in soils through agriculture can play an important role in mitigating climate change. Although the calculated values represent important contributions, the hope of putting all these techniques into practice quickly on a global scale is not realistic. But because the benefits of regenerative agriculture are so rich, as outlined above, there should be an overarching interest in investing in regenerative agricultural methods.