Shall I not have intelligence with the earth?

Am I not partly leaves and vegetable mould myself?

— Henry David Thoreau[1]

When I studied soil fertility as a graduate student in the mid–1960s, soil organic matter was recognized as something that occurred, but it received little emphasis in textbooks or class discussions. There were a few courses on soil biology, but the focus of practical soil fertility studies was on individual elements needed by plants, how they behaved in soil, and how to determine if they were present in sufficient amounts in forms that were available for plants to use. We, of course, concentrated on the elements taken up from the soil in relatively large amounts that were commonly found to be deficient—nitrogen, phosphorus, and potassium. If additions of particular nutrients were needed, we learned how much should be added, which fertilizer should be used, and how and when best to apply it. Growing legumes to supply the following crops with nitrogen may have been mentioned in passing, but the overwhelming emphasis was on commercial fertilizers. The “law of the minimum” holds that there will be one element, for example nitrogen, that will be most deficient. But if we added the right amount of nitrogen fertilizer to correct the deficiency, then lack of sufficient phosphorus or potassium (or some other nutrient) might limit yield. Thus, we needed to be sure that no elemental deficiency would limit plant growth. But having a sufficiency of the essential elements is only one characteristic of soil health, a much broader concept than the old-fashioned one of “soil fertility.”

Global Cycles and Flows

There are a number of important flows and cycles that operate on local, regional, and global levels. Flows occur when substances move from one location to another. A cycle is a type of flow in which the substance returns to the general location from which it came. On a very local level, a true cycle will occur when nutrients removed from soil by an annual plant return to the soil when the plant dies. Even if eaten partially by an insect or herbivore, most of the nutrients will normally return to soil not that far away. The hydraulic cycle, in contrast, functions on a more regional or global level, as water is evaporated from plant leaves or from lakes and the ocean, travels in the atmosphere for some distance, and then falls to earth as rainfall or snow. An example of a flow that is not a cycle is the erosion of soil as water rushes over its surface, with the eroded sediments flowing via streams and rivers to be deposited on the ocean floor.

Organic material in soil is a prominent reservoir of terrestrial carbon and participates in the global cycling of carbon. A portion of atmospheric carbon dioxide removed by plants is deposited in soil as roots and aboveground residues that become incorporated by the action of earthworms or other larger organisms. Some of this organic material (carbon) remains in the soil and a portion is used as food by soil organisms, such as bacteria and fungi, emitting carbon dioxide that diffuses back into the atmosphere. In healthy soil, there is a large turnover of carbon as a portion of the residues added provide the food source for “a main repository of terrestrial biodiversity, harboring roughly one-quarter of all species on Earth.”[2] As the multitude of organisms go about their activities, soils breathe as if a single organism, with oxygen diffusing downward and carbon dioxide diffusing back into the atmosphere, completing a cycle.

About three times as much carbon is stored in soils than occurs in the atmosphere as carbon dioxide. A soil that has 1 percent organic matter (or about 0.6 percent carbon) in its surface seven inches would be holding the approximate equivalent of the carbon in the carbon dioxide in the atmosphere above the field.[3] And the surface layer of temperate region soils normally contain between 1 to 6 percent organic matter. How much is present in a particular soil depends on many factors.

Over many years, individual soil types develop their unique characteristics as a result of the combined effects of the local climate and the vegetation growing on them, as well as the sources of minerals (parent material) from which a soil develops. As years pass, soils on the bottom of slopes receive eroded soil from the side slopes. This depletes the side slopes of organic matter-enriched topsoil at the same time that soils at the bottom become enriched.

As soils develop from various deposits such as windblown silts (loess), along river banks or former lake bottoms, or from disintegrating rocks, organic matter tends to accumulate as roots die and are replaced by new ones, and as the secretion from roots provides food for numerous organisms. As much as half of substances produced during photosynthesis by plant leaves are transported to roots for respiration and then out of the roots, adding directly to the soil’s supplies of organic materials. Some is used for growing new roots and some is exuded into the zone around roots, the rhizosphere, supporting the growth of large populations of a wide variety of organisms. When soils are young, more organic residue is added than is decomposed by soil organisms, and organic matter content accumulates, finally reaching a plateau. This means that under natural conditions soils tend to be sinks for carbon for long periods of time. Thus, in undisturbed soils a portion of the carbon removed from the atmosphere commonly flows into the soil and stays there. The level of the organic matter “plateau” that accumulates is dependent on a number of factors, such as the type of minerals present, climate, and type of vegetation.

Carbon, Life, and Soil

Carbon is the element that provides the backbone for the structure of organic molecules used by all living organisms. Substances based on carbon provide the energy for most life, including humans. But where does the carbon and energy contained in these molecules come from? As green plants use the sun’s energy to perform photosynthesis, carbon dioxide is captured from the atmosphere and used to make the multitude of compounds that the plant needs. The carbohydrates (sugars, starch), lipids, and proteins, formed from the products of photosynthesis during the growth of plants, all contain carbon that came from the atmosphere. They also contain energy stored in their molecular structure for later use by the plant or by an organism that consumes the plant.

Aside from fish and other aquatic organisms, all the food we consume is derived from land plants either directly or indirectly, as when we eat products of animals that subsisted on plants. In other words, we depend on plants that grow in (through roots) and on soil. Plants grown in farm fields provide the energy that we need to live and the carbon to make the organic chemicals in our bodies. Plants are around 50 percent carbon on a dry weight basis, but they also contain another sixteen chemical elements essential to their growth and reproduction. And while the carbon in plants is derived from the atmosphere, and some atmospheric oxygen is used as plants respire (although plants give off more oxygen as a byproduct of photosynthesis than they use in respiration), other needed elements are supplied by the soil. Therefore, the calcium and phosphorus in bones and teeth, nitrogen in our proteins, the sulfur, potassium, magnesium, and other elements inside animals are all first taken up from the soil by plants. The soil is not just a place to anchor the plant; it is the source of the plant’s water supply as well as the minerals it needs. The soil is thus the source of the energy we need and obtain from a healthy diet. It is literally true, as the Old Testament of the Hebrew Bible says, “for soil thou art.”[4] A brief summary of the importance of soil is provided by a report by the European Commission’s Board for Soil Health and Food:

Life on Earth depends on healthy soils. The soil under our feet is a living system – home to many fascinating plants and animals, whose invisible interactions ensure our well-being and that of the planet. Soils provide us with nutritious food and other products as well as with clean water and flourishing habitats for biodiversity. At the same time, soils can help slow the onset of climate change and make us more resilient to extreme climate events such as droughts and floods. Soils preserve our cultural heritage and are a key part of the landscapes that we all cherish. Simply put, healthy living soils keep us, and the world around us, alive.[5]

Soil carbon is found in two general forms—as organic material and as a component of minerals, such as limestone (calcium carbonate, CaCO3). In humid regions, almost all carbon is in organic forms (soil organic matter), except in subsurface layers of soils derived from limestone. In arid regions, it is common to find lime even in surface soil. The discussion of soil carbon will refer exclusively to organic forms of carbon.

What Is Soil Organic Matter?

Soil organic carbon is another term for organic matter. Over a hundred years ago, soil organic matter was described in an agricultural publication as the “living,” the “dead,” and the “very dead.” The living—plant roots and the myriad organisms living in and around the roots as well as in the bulk soil—represent about 15 percent of soil carbon. The dead refers to the relatively fresh residues of deceased plants, animals, bacteria, and other organisms all in various stages of being decomposed as they are used as food sources by living organisms. The “very dead” is organic matter in late stages of decomposition, sometimes relatively stable, or otherwise not very available for organisms to use. Char (black carbon), formed when vegetation burns and residue later becomes incorporated in soil, is also very stable. As mentioned, when organisms metabolize as they decompose residues, they give off carbon dioxide, which then diffuses upward, back into the atmosphere. However, a portion of the soil’s organic residue is “trapped” inside soil aggregates or adheres tightly to clay particles and becomes inaccessible to decomposing organisms. These sources are much more stable than other organic materials in soil and will accumulate over time.

Soil Rifts Recognized and Unrecognized: Nutrients vs. Organic Matter

Large rifts and disturbances in many important flows and cycles in soils have appeared over the last few hundred years, accelerating especially after the Second World War—in the carbon cycle, nitrogen cycle, hydraulic (water) cycle, and general cycling of nutrients. The rapidly occurring disturbances of nature’s cycles have many implications for humans and other organisms that have evolved and grown in population under mostly slowly changing conditions.

The rift in nutrient cycling was recognized by Justus von Liebig during the nineteenth century when more and more food, instead of being consumed locally, was transported from the countryside to cities, and even between countries. As this occurred, nutrients contained in food crops and animals leaving the farm were not being returned to the fields. To keep nutrients (and human waste in which they were contained) from accumulating in cities, such wastes were mostly discharged into rivers. In other words, a portion of the nutrients that once cycled back into the soil on peasant farms now did not return to the land but rather participated in a flow, becoming water pollutants along the way. This one-way flow resulted in a depletion of soil nutrients needed to produce future crops. Karl Marx, following Liebig, explained this in the first volume of Capital:

Capitalist production, by collecting the population in great centers, and causing an ever increasing preponderance of town population… disturbs the circulation of matter between man and the soil, i.e., prevents the return to the soil of its elements consumed by man in the form of food and clothing; it therefore violates the conditions necessary to lasting fertility of the soil.[6]

This remains a problem to the present time, with most human waste in cities contaminated with a variety of toxic metals and industrial organic chemicals. Thus, it is unwise to apply many sewage sludges to farmland. This problem and the one arising from factory farms that have separated animals from the land on which their feed is raised—creating an overabundance of nutrients near the animals while cropland is in constant need of added fertilizer to replenish lost nutrients—have resulted in the need to apply vast quantities of commercial fertilizers to most agricultural soils.

What remained unrecognized by Western scientists in the nineteenth century was that the depletion of soil organic matter was an even greater threat to preserving the “lasting fertility of the soil” than was the depletion of nutrients. However, in 1911, after returning from extensive travels, the U.S. Department of Agriculture’s Franklin H. King published his Farmers of Forty Centuries in which he maintained that the key to the continuous productive agriculture in East Asia was the judicious cycling of nutrients back to the soil. King wrote about farmers in China: “Manure of all kinds, human and animal, is religiously saved and applied to the fields in a manner which secures an efficiency far above our own practices.”[7] True, this is nutrient cycling. But the return of human and farm animal manures to soil is also adding organic matter.

Rift in the Flows and Cycles of Soil Carbon

The level of organic matter in undisturbed soils comes into equilibrium depending on the multiple factors discussed. However, when soils are disturbed by digging with a spade or by plowing or harrowing, the soil structure is broken up and particles of organic matter that were not accessible to organisms because they were inside of aggregates, as well as oxygen in the atmosphere, all of a sudden become available. This causes a burst of biological activity that frees some nutrients for plants to use, but also causes a huge increase in organic matter decomposition, with carbon converted to carbon dioxide and diffusing up into the atmosphere above. Generally, this converts soils from being carbon sinks to carbon sources, with the net effect of enriching the atmosphere with carbon dioxide instead of removing it. During the conversion process from forest or grassland to agricultural soil, a lot of organic matter is lost, as carbon dioxide flows to the atmosphere. And while the rate of loss may slow down after a few years, soils can continue to be carbon dioxide sources for years after their conversion to farming. The changing land use from forests and grasslands to farming, aided by increasingly large tractors and implements able to work immense fields, has contributed substantial quantities of carbon dioxide to the atmosphere, contributing to global warming and climate destabilization. Leading soil scientist Rattan Lal has estimated that some 110 to 130 billion tons (gigatons) of carbon have been lost from agricultural soils. (This is quite large when compared to the 10 gigaton annual contribution estimated for fossil fuels.)[8] Methane (CH4), another greenhouse gas that contains carbon, is also lost from flooded agricultural soils during rice production.

While farming practices contributed to atmospheric greenhouse gases, there is a major additional problem—as soil organic matter becomes depleted, soils become less healthy. Soils may lose half of the organic matter (carbon) when farmed for many years. So the loss of soil organic matter and the corresponding massive carbon relocation to the atmosphere (as carbon dioxide) constitutes the soil carbon rift. As soil organic matter decreases as a result of the rift, soils hold less water, provide lower levels of nutrients to plants, and have lower biological diversity. As the soil structure deteriorates, plants become more susceptible to disease and insects. As less water is able to infiltrate, more runs off, carrying soil particles. A downward spiral occurs, with lower organic matter leading to more erosion of topsoil and more loss of organic matter, severely degrading soil in an accelerating, self-reinforcing feedback loop.

It is estimated that about one-third of the world’s soils have become significantly degraded. While there are a number of ways that soil degradation occurs, the rift in the atmosphere-soil carbon flow and cycle has had a greater long-term detrimental effect on farming than the rift in the nutrient cycle that concerned nineteenth-century agricultural scientists. If a soil is low in available nitrogen or phosphorus, adding fertilizer containing these elements can greatly increase yields. This emphasis on nutrients led to the focus on commercial fertilizers—especially nitrogen, phosphorus, and potassium—as the major way to improve soil, becoming the basis for a massive agro-chemical industry. At the same time, other soil issues were not pursued with the same vigor.

It Fell Like Lucifer

It was long thought that soil organic matter was important for soils and was responsible for the dark color of the surface layer, or topsoil. In 1676, John Evelyn wrote about what we now call topsoil, the upper layer that is highly enriched in organic matter (referred to as mould): “I begin with what commonly first presents it self under the removed Turf, and which, for having never been violated by the Spade, or received any foreign mixture, we will call the Virgin-Earth; not that of the Chymists, but as we find it lying about a foot deep, more or less, in our Fields, before you come to any manifest alteration of colour or perfection. This surface-Mould is the best, and sweetest.”[9]

Two centuries later, Charles Darwin used the terms vegetable mould and humus to refer to topsoil that is enriched in organic matter and described how earthworms helped to form “the dark coloured, rich humus which almost everywhere covers the surface of the land with a fairly well-defined layer or mantle.”[10]

Once it was discovered that carbon was so important to plants, the question became: Where did the carbon in plants come from? Some believed that the carbon for plants came from carbonaceous material in soil organic matter. But in 1804, the Swiss scientist Théodore de Saussure published a book containing results of experiments demonstrating that the carbon in plants, and therefore most of their dry weight, comes from the atmosphere and not from the soil. It took until late in the century for the importance of his work to become widely accepted.

In the mid–nineteenth century, the “father” of agricultural chemistry, Liebig, claimed that “the Belief in the value of Humus [organic matter] no longer exists” and that what was important was rather for soils to contain good quantities of the essential elements that plants need.[11] Manufactured fertilizers could replace the effects of applying manure—“the salts of ammonia had taken the place, and produced the effect of the decaying organic matter.”[12] Liebig thought that organic matter helped some soils and may hurt others, but that what was really critical was the presence of sufficient quantities of essential elements such as nitrogen, phosphorus, and potassium.

With so much of plants derived from the atmosphere and the increased stress on the importance of soil nutrients, the appreciation of the significance of soil organic matter declined. In 1908, three Vermont scientists colorfully described this transition: “Once extolled as the essential soil ingredient, the bright particular star in the firmament of the plant grower, it [humus] fell like Lucifer when the agricultural chemists of the second quarter of the last century demonstrated the aerial origin of the major part of the plant structure.”[13]

The Importance of Soil Organic Matter (Organic Carbon)

In the first decade of the twentieth century, the aforementioned three scientists were tasked with finding out why the soils of Vermont had become so deteriorated. “It is usually said that the soil is exhausted, run down, worn out, and the popular notion is that its plant food content if not absolutely gone is at least reduced to a minimum.… This common conception of the nature of the difficulty and as to what constitutes ‘fertility’ is incomplete. It over-emphasizes the chemical phase. Fertility and plant food are not synonymous terms.”[14]

The conclusion of their study was that, although there were other explanations, “the depletion of the soil humus [organic matter] supply is apt to be a fundamental cause of lowered crop yields. The one crop system, fallowing, shortage of manure, no green manuring; the non-use of legumes or grasses in the rotation; deforestation, fires, the continued use of commercial fertilizers; all these tend unduly to lower the humus content.”[15] It took close to a century for scientists and farmers to fully recognize the overwhelming importance of soil organic matter—something that was clear to those scientists in the “backwater” state of Vermont in 1908.

Soil organic matter is so critical to soil health because it improves essentially all soil biological, chemical, and physical properties. It provides food for stimulating biological activity and diversity in the bulk soil and near roots—the microbiome surrounding and on plant roots is every bit as important to plant health as the human microbiome in the gut is to ours. It also helps soil particles clump together into aggregates, thereby enabling greater rainfall infiltration and water storage. It also is a storehouse of nutrients for plants to use, slows down changes in acidity, makes soil less prone to compaction, and so on. One of the ways to understand the importance of soil organic matter is to study what happens when it declines. As organic matter decreases, there is a decrease in the diversity and activity of soil organisms; soil structure deteriorates; erosion intensifies because more water runs off the field during intense rainstorms, taking soil particles with it; water infiltration and water storage for plants to use later decreases; the soil becomes more prone to compaction; and crop yields decrease.

What Is the Problem?

As organic matter declines and farmers use poor or no crop rotations as well as intensively till their soils—leaving soil bare for long periods—the following problems start to occur: low nutrient availability; low water-holding capacity; soil compaction; and increasing problems with plant diseases and insect infestations. The conventional answer has been to view the “problems” that develop as separate issues, each dealt with by its own remedy: applying more fertilizers, irrigating more frequently, using fungicides and insecticides, and employing heavy equipment to try to breakup compact layers. These “remedies,” of course, then create problems of their own; such as fertilizers and pesticides contaminating ground and surface waters, and the creation of insect and weed resistance to pesticides (causing a pesticide treadmill as new pesticides are introduced and higher levels of older ones are used).

Rather than viewing these negative occurrences as “problems,” they are better understood as symptoms of a deeper underlying problem: unhealthy soils. Once understood in this way, a whole different approach is needed. Promoting the formation of healthy soils implies a preventive approach (instead of the reactive one described above that reacts to each “problem” as if an isolated incident), one that encourages practices that minimize the development of conditions that harm the yields of plants. It strives to mimic the strengths of undisturbed natural systems and to create conditions that are optimal for plants—especially a high population of active and diverse soil organisms, optimal availability of plant nutrients, good soil structure for root exploration as well as for good water storage, with minimal rainfall runoff and erosion, and low levels of compaction. Building soil health is really about enhancing the soil habitat so that plants can grow to their full potential, just like we need to pay attention to enhancing the field’s aboveground habitat. Building up and maintaining organic matter, while not the only issue, is at the heart of developing healthy soils.[16]

Healthy Soils

To create and preserve a permanent thriving agriculture for untold generations to come, it is essential to manage and care for soils using practices that build and maintain healthy soils. There are three general aspects of a healthy soil: chemical, biological, and physical. Chemically, a healthy soil has moderate pH (acid/base status), sufficient stores of nutrients for plants to grow, and contains no chemicals that harm plants. Biologically, it contains a diverse and active population of organisms, from microorganisms such as bacteria and fungi to small-size animals such as nematodes and mites to larger ones like earthworms and beetles. It is diversity of organisms in the soil that helps keep potential plant disease or soil-borne insect pests under control. A significant number of soil organisms also promote plant growth in a variety of ways by helping make nutrients more available, inducing plants to produce chemicals to defend themselves from diseases, and providing chemicals that stimulate plant growth. Mycorrhizae, a group of fungi, are especially important because they enter the root while their thin hyphae grow into the bulk soil (sometimes connecting to other plants) and, while getting sustenance from the plant, help transport water and phosphorus to roots. And physically, a healthy soil has a structure that allows plant root systems to easily explore and develop, permits rainfall to easily infiltrate (and not runoff the field), and is able to store a lot of water to supply plants between rainfall or irrigation events.

Carbon Storage (Sequestration) in Soils

The Earth is already too warm and even if fossil fuel use can be eliminated soon, it will get warmer with feedback loops already occurring continuing to increase greenhouse gas emissions. Thus, climate scientists suggest we should have plans for carbon dioxide drawdown (“negative emissions”). James Hanson and coauthors advocate these should include “improved agricultural and forestry practices, including reforestation and steps to improve soil fertility and increase its carbon content.”[17] In order to have a meaningful impact on the problem, these activities would need to be carried out over vast portions of the world.

Since many soils are depleted in organic matter and increasing organic matter has such profound positive effects on soil health and there is too much carbon in the atmosphere (as carbon dioxide), it certainly makes sense to promote practices that increase soil organic matter contents. An example of proposals for “carbon sequestration” is the French 4 per 1000 initiative to increase soil organic matter by 0.4 percent a year.[18] Of all the proposals to try to draw down atmospheric carbon dioxide (many of which involve large-scale geoengineering), those that also help to heal the rift in the soil carbon cycle make the most sense. And for the sake of the environment and farming, soil health promotion programs should be undertaken everywhere to help farmers enhance the productivity of their soils.

Significantly increasing soil organic matter on all (or most) of the world’s agricultural soils is not a trivial undertaking. This would require continuous large government initiatives for farmer education and assistance. However, carbon sequestration in soil is not a “magic bullet” to combat global warming that some believe. If large quantities of carbon could be sequestered in soils it would only slow down the rate of carbon dioxide increase in the atmosphere. In addition, as organic matter increases, the rate of increase slows down and finally comes to an end: soils have a finite capacity to store carbon as organic matter. Thus, carbon sequestration in soils is no substitute for rapidly decreasing the use of fossil fuels.

With the increased attention on the use of soil as a place to store carbon, new schemes pop up from time to time. For example, one involves annual applications of massive quantities of rock dust (ground up rock) to vast areas of farmland, with chemical reactions supposedly converting carbon dioxide to other chemical forms as the dust undergoes breakdown and chemical reactions (weathering). Another has proposed to breed crops with larger root systems because a given weight of roots, already being in the soil, adds more to soil organic matter over time than does the same amount of crop residue on the surface. There are practical and theoretical problems with each of these proposals.[19]

Building Healthier Soils

Instead of concentrating only on carbon storage in soils, practices that contribute to developing healthy soils should be promoted worldwide for the sake of farmers, especially resource-poor ones, and the environment. Healthy soil is not just an issue of removing carbon dioxide from the atmosphere by storing more carbon, although that will happen. Healthy soils mean less pesticide and commercial fertilizer use—both of which are energy intensive to produce and frequently result in environmental pollution. (The production of nitrogen fertilizers uses fossil fuel both as a feedstock and an energy source to drive the process. Compare this with nitrogen production by legumes, using the sun’s energy to produce forms of nitrogen that plants can use.) There will also be less runoff and erosion, resulting in more water storage in soil for plants to utilize as well as cleaner surface waters. Thus, healthy soils are more resilient to drought periods and intense rainfall occurring more frequently because of climate destabilization.

There is no exact recipe or formula for improving soil health because practices need to be modified and customized for each farm, its soils, and the crops grown and animals raised. However, there are general approaches that apply widely.

The example practices listed all contribute to one or more of the following: growing healthy plants with strong defense capabilities, promoting beneficial organisms, and suppressing pests.[20] Many may help to maintain or increase soil organic matter (carbon sequestration).

• Keeping the soil covered with living vegetation (and living roots in the ground) for as much of the year as possible by using cover crops between economic crops.
• Reducing soil disturbance (tillage) using appropriate equipment, keeping crop residue on the surface.
• Using complex rotations, including perennials if possible, and intercropping to provide diversity above and below ground.
• Using legumes to “grow nitrogen” for grains and vegetables.
• Adding appropriate amounts of varied sources of organic matter on a regular basis by growing high biomass crops and cover crops, or bringing materials such as manures, composts of manures, and kitchen wastes to the field.
• Integrate animals into cropping systems.

The recognition of the importance of soil health—including the need to increase soil organic matter in most of the world’s soils—has spread from the scientific community to make inroads in the farming community, as well as national and international agricultural agencies such as the U.S. Department of Agriculture and the United Nations Food and Agriculture Organization. But most farmers rely on agricultural industries for information. These industries are behind most of the promotion of farming techniques, especially those that involve inputs such as seeds, fertilizers, pesticides, and equipment. Because there is little money to be made by private companies promoting ecological practices that build healthy soils and use few inputs from off the farm, immense multifaceted government outreach and programs will be needed to advance widespread implementation of such practices.

If the needed outreach programs can be successfully implemented on a large portion of the world’s agricultural soils, the soil carbon rift can be healed (drawing a portion of carbon dioxide out of the atmosphere to be stored as soil organic matter) while the multitude of positive effects of good soil organic matter management and other ecological soil practices will improve crop yields, decrease pollution from farming, and increase resilience of fields and farmers in the face of climate instability.

Notes

1. Henry David Thoreau, Walden and Civil Disobedience (Nashville: American Renaissance, 2010), 73.
2. Carlos Guerra et al., “Tracking, Targeting, and Conserving Soil Biodiversity,” Science 371, no. 6526 (2021): 270–71.
3. For calculations, see Fred Magdoff and Chris Williams, Creating an Ecological Society: Toward a Revolutionary Transformation (New York: Monthly Review Press, 2017), 344, note 15.
4. Even though the Hebrew word afar (עָפָר) is translated in the King James version (Genesis 3:19) as dust, it is better translated as earth or soil in the context in which it is used. There are also two other Hebrew words for earth or soil—adamah (from which the name Adam is derived, giving more credence to the translation of “for soil thou art”) and karka.
5. Cees Veerman et al., Caring for Soil Is Caring for Life (Luxembourg: European Union, 2020).
6. Karl Marx, Capital, vol. 1 (London: Penguin, 1976), 637–38.
7. Franklin H. King, Farmers of Forty Centuries (1911; repr. Mineola: Dover, 2004), 9.
8. Virginia Gewin, “The World Food Prize Winner Says Soil Should Have Rights,” Civil Eats, July 15, 2020.
9. John Evelyn, “A Philosophical Discourse of Earth, Relating to the Culture and Improvement of It for Vegetation, and the Propagation of Plants, & c.” (lecture, Royal Society, London, April 29, 1675).
10. Charles Darwin, The Formation of Vegetable Mould (London: John Murray, 1904), e-book available on the Project Gutenberg website.
11. Justus von Liebig, Letters on Modern Agriculture (New York: John Wiley, 1859), Letter IV, xxii.
12. Liebig, Letters of Modern Agriculture.
13. L. Hills, C. H. Jones, and C. Cutler, 1908. “Soil Deterioration and Soil Humus,” Section VIII, Vermont Agricultural Experiment Station Bulletin 135 (1908), 142–77.
14. Hills, Jones, and Cutler, “Soil Deterioration and Soil Humus.”
15. Hills, Jones, and Cutler, “Soil Deterioration and Soil Humus.”
16. Ray R. Weil and Fred Magdoff, “Significance of Soil Organic Matter to Soil Quality and Health,” in Soil Organic Matter in Sustainable Agriculture, ed. Magdoff and Weil (Boca Raton: CRC, 2004), 1–43; Fred Magdoff and Ray R. Weil, “Soil Organic Matter Management Strategies,” in Soil Organic Matter in Sustainable Agriculture, 45–65; Fred Magdoff and Harold van Es, Building Soils for Better Crops, 3rd ed. (Brentwood: Sustainable Agriculture Research and Education, 2009).
17. James Hanson et al., “Young People’s Burden: Requirement of Negative CO2 Emissions,” Earth System Dynamics 8 (2017): 577–616.
18. You can find out more about the 4 per 1000 initiative at their website org.
19. Please correspond with the author for some thoughts on these proposed carbon sequestration schemes. There are promising developments, such as the breeding of perennial grain crops at the Land Institute in Salina, Kansas. Kernza® grain was developed from a type of wheatgrass and has an extensive root system (much greater than wheat), which, combined with its perennial growth, will positively impact organic matter levels. Though not specifically breeding for more root growth, perennial grasses tend to have larger root systems than annual grains.
20. Magdoff and van Es, Building Soils for Better Crops. A new edition of the book will be available in mid– to late 2021 and will be available at sare.org. All PDF copies of Sustainable Agriculture Research and Education publications are available to download without cost. Hard copies available.

[Fred Magdoff is professor emeritus of plant and soil science at the University of Vermont. He is the author and editor of numerous books. Article courtesy: Monthly Review, a socialist journal published from New York.]